阅读说明：本技术 磁盘用铝合金坯体和磁盘用铝合金基片 (Aluminum alloy blank for magnetic disk and aluminum alloy substrate for magnetic disk ) 是由 吉崎宥章 泉孝裕 大塚泰史 梅田秀俊 于 2020-02-12 设计创作，主要内容包括：提供一种耐冲击性和Ni－P镀膜表面的平滑性优异的磁盘用铝合金坯体和磁盘用铝合金基片。本发明的磁盘用铝合金坯体和磁盘用铝合金基片,以规定量含有Mg、Cr,并有Cu、Zn、Mn、Fe、Si在规定量以下(或低于规定量),余量由Al和不可避免的杂质构成,并规定了Mg－Si系金属间化合物的最大长度。(An aluminum alloy base material for a magnetic disk and an aluminum alloy substrate for a magnetic disk excellent in impact resistance and smoothness of Ni-P plated film surface are provided. The aluminum alloy blank for a magnetic disk and the aluminum alloy substrate for a magnetic disk of the present invention contain predetermined amounts of Mg and Cr, and Cu, Zn, Mn, Fe and Si are contained in predetermined amounts or less (or less than predetermined amounts), and the balance is made up of Al and unavoidable impurities, and the maximum length of the Mg-Si intermetallic compound is defined.)

1. An aluminum alloy base material for a magnetic disk, characterized by comprising

Mg: 5.0 to 7.0 mass%,

Cr: 0.05 to 0.35 mass%, and,

cu: 0.10 mass% or less,

Zn: 0.40% by mass or less,

Mn: less than 0.10 mass%,

Fe: 0.025 mass% or less,

Si: 0.025 mass% or less of a surfactant,

the balance of the alloy contains Al and inevitable impurities,

the maximum length of the Mg-Si intermetallic compound on the surface is 3 μm or less.

2. An aluminum alloy base material for a magnetic disk, comprising a core material and a skin material provided on at least one surface of the core material,

the leather material comprises

Mg: 5.0 to 7.0 mass%, and,

Cr: 0.05 to 0.35 mass%, and,

cu: 0.10 mass% or less,

Zn: 0.40% by mass or less,

Mn: less than 0.10 mass%,

Fe: 0.025 mass% or less,

Si: 0.025 mass% or less of a surfactant,

the balance of the alloy contains Al and inevitable impurities,

the maximum length of the Mg-Si intermetallic compound on the surface is 3 μm or less.

3. The aluminum alloy base material for magnetic disks as claimed in claim 1 or claim 2, wherein the yield strength is 140MPa or more.

4. An aluminum alloy substrate for a magnetic disk, characterized by comprising

Mg: 5.0 to 7.0 mass%, and,

Cr: 0.05 to 0.35 mass%, and,

cu: 0.10 mass% or less,

Zn: 0.40% by mass or less,

Mn: less than 0.10 mass%,

Fe: 0.025 mass% or less,

Si: 0.025 mass% or less of a surfactant,

the balance of the alloy contains Al and inevitable impurities,

the maximum length of the Mg-Si intermetallic compound on the surface is 3 μm or less.

5. An aluminum alloy substrate for a magnetic disk, comprising a core material and a skin material provided on at least one surface of the core material,

the leather material comprises

Mg: 5.0 to 7.0 mass%, and,

Cr: 0.05 to 0.35 mass%, and,

cu: 0.10 mass% or less,

Zn: 0.40% by mass or less,

Mn: less than 0.10 mass%,

Fe: 0.025 mass% or less,

Si: 0.025 mass% or less of a surfactant,

the balance of the alloy contains Al and inevitable impurities,

the maximum length of the Mg-Si intermetallic compound on the surface is 3 μm or less.

6. The aluminum alloy substrate for a magnetic disk as recited in claim 4 or claim 5, wherein the yield strength is 140MPa or more.

Technical Field

The present invention relates to an aluminum alloy blank for a magnetic disk and an aluminum alloy substrate for a magnetic disk.

Background

With the digitization of information and the spread of the internet, a large amount of digital data is handled, and a large capacity of a Hard Disk Drive (HDD) is required around a data center. In order to increase the capacity of the HDD, the number of mounted magnetic disks per HDD is increased, and therefore, thinning of the magnetic disks is being studied.

In the study of the thinning of the magnetic disk, it is proposed to reduce the thickness of the magnetic disk mounted on the 3.5-inch HDD from about 1.3mm to 0.8mm or less.

Here, as a problem of thinning the magnetic disk, deformation of the magnetic disk due to impact at the time of dropping can be cited. Further, as a HDD having a large capacity, a HDD having a large outer diameter of 3.5 inches has been mainly used, but the maximum bending stress is reduced and the HDD is easily deformed as the outer diameter is increased.

Such deformation of the magnetic disk can be dealt with by improving the impact resistance of the base material and the substrate after the correction annealing. However, with the increase in the capacity of HDDs and the reduction in the thickness of magnetic disks, the level of impact resistance required for magnetic disk materials has also increased.

In addition, for example, a material for magnetic disks is required to have excellent plating properties, i.e., a property of preventing plating defects such as buildup, gas pits, and bubbling from occurring after electroless Ni — P plating of a substrate. When a plating defect occurs, the smoothness of the Ni — P plating film surface is reduced.

The following techniques have been proposed for such a magnetic disk material.

For example, patent document 1 discloses a method for producing an aluminum alloy substrate for a magnetic disk, which satisfies contradictory properties of grain refinement and reduction of plating pit defects at the same time.

Further, for example, patent document 2 discloses an aluminum alloy blank for a magnetic disk and an aluminum alloy substrate for a magnetic disk, which have sufficient impact resistance to the extent that they are not deformed by impact at the time of falling even when they are thinned, and which are less likely to cause fine waviness in a plated surface after plating and less likely to cause surface defects.

[ Prior art documents ]

[ patent document ]

[ patent document 1 ] Japanese patent No. 5199714 publication

[ patent document 2 ] Japanese patent No. 5815153 publication

In patent document 1, although studies have been made on reduction of plated pit defects with respect to an aluminum alloy substrate for a magnetic disk, impact resistance has not been sufficiently studied.

Therefore, the technique described in patent document 1 still has room for improvement in impact resistance.

On the other hand, in patent document 2, studies have been made on impact resistance as well as reduction of surface defects with respect to a base material and a substrate for a magnetic disk.

However, the technique described in patent document 2 may contain relatively large amounts of Mn in the green body and the substrate, and at this Mn content, the grindability (the degree of easy grindability during processing) may be reduced.

Therefore, it has been desired to create a base material and a substrate for a magnetic disk which have excellent impact resistance and smoothness of the Ni-P plating film surface, unlike the technique described in patent document 2, in which the Mn content is relatively large.

Disclosure of Invention

Accordingly, an object of the present invention is to provide an aluminum alloy base material for magnetic disks and an aluminum alloy substrate for magnetic disks, which are excellent in impact resistance and smoothness of Ni-P-plated surfaces.

The aluminum alloy blank for a magnetic disk and the aluminum alloy substrate for a magnetic disk of the present invention contain Mg: 5.0 to 7.0 mass%, Cr: 0.05 mass% or more and 0.35 mass% or less, and satisfies Cu: 0.10 mass% or less, Zn: 0.40 mass% or less, Mn: less than 0.10 mass%, Fe: 0.025 mass% or less, Si: 0.025 mass% or less, the balance comprising Al and unavoidable impurities, and the maximum length of the Mg-Si based intermetallic compound on the surface being 3 μm or less.

Further, the aluminum alloy blank for a magnetic disk and the aluminum alloy substrate for a magnetic disk of the present invention are provided with a core material and a skin material provided on at least one surface of the core material, wherein the skin material contains Mg: 5.0 to 7.0 mass%, Cr: 0.05 mass% or more and 0.35 mass% or less, and satisfies Cu: 0.10 mass% or less, Zn: 0.40 mass% or less, Mn: less than 0.10 mass%, Fe: 0.025 mass% or less, Si: 0.025 mass% or less, the balance comprising Al and unavoidable impurities, and the maximum length of the Mg-Si based intermetallic compound on the surface being 3 μm or less.

With this constitution, the aluminum alloy base material for magnetic disk and the aluminum alloy substrate for magnetic disk are excellent in impact resistance and smoothness of Ni-P plated surface.

In addition, the aluminum alloy base sheet for a magnetic disk and the aluminum alloy blank for a magnetic disk of the present invention preferably have a yield strength of 140MPa or more.

With this structure, the aluminum alloy base sheet for a magnetic disk and the aluminum alloy base sheet for a magnetic disk can exhibit more excellent impact resistance.

The aluminum alloy base material for a magnetic disk and the aluminum alloy substrate for a magnetic disk of the present invention are excellent in impact resistance and smoothness of the Ni-P plated surface.

Drawings

FIG. 1 is a schematic view showing an impact resistance tester for evaluating impact resistance.

FIG. 2 is a schematic view of an HDD mounted with a green body used for impact resistance evaluation.

Fig. 3 is a graph showing the relationship between the yield strength of the green body and the amount of change in flatness.

Detailed Description

Hereinafter, the embodiments of the aluminum alloy blank for a magnetic disk (hereinafter, simply referred to as blank) and the aluminum alloy substrate for a magnetic disk (hereinafter, simply referred to as substrate) for carrying out the present invention will be described in detail.

[ base material ]

The green body of the present embodiment contains Mg and Cr in predetermined amounts, Cu, Zn, Mn, Fe, and Si in amounts less than or equal to predetermined amounts, and the balance is made of Al and unavoidable impurities.

In the green body of the present embodiment, the maximum length of the Mg — Si intermetallic compound on the surface is preferably not more than a predetermined value, and the yield strength is preferably not less than a predetermined value.

Hereinafter, each configuration will be described in detail.

(Mg: 5.0 mass% or more and 7.0 mass% or less)

Mg is an element effective for increasing the yield strength of the body. If the amount of Mg is less than 5.0 mass%, a sufficient yield strength cannot be obtained, and the impact resistance of the green body is lowered. On the other hand, if the Mg content is higher than 7.0 mass%, the crack sensitivity at high temperature becomes high. Therefore, cracks are likely to occur during hot rolling, and rolling becomes difficult.

Therefore, the Mg amount is 5.0 mass% or more and 7.0 mass% or less. From the viewpoint of obtaining a higher yield strength, the Mg content is preferably 5.5 mass% or more, and more preferably 6.0 mass% or more. In addition, the Mg content is preferably 6.5 mass% or less from the viewpoint of reducing crack sensitivity at high temperatures.

(Cr of 0.05 to 0.35 mass%)

Cr is an element effective for increasing the yield strength of the green body. Cr is crystallized as a fine compound during casting, and is precipitated as a fine compound during the homogenization heat treatment, thereby suppressing grain growth during the homogenization heat treatment and the hot rolling treatment. In addition, Cr suppresses abnormal growth of recrystallized grains, and has the effect of homogenizing the structure. If the amount of Cr is less than 0.05 mass%, these effects cannot be obtained. On the other hand, if the Cr content is more than 0.35 mass%, the effect of suppressing the grain growth becomes excessive, and the recrystallized structure after the correction annealing is not in an equiaxed state but in a state of being elongated in the rolling direction. This increases the anisotropy of the structure, and deteriorates the smoothness of the Ni-P plating film surface. When the Cr content is more than 0.35% by mass, coarse Al-Cr intermetallic compounds are crystallized as primary crystals during casting, and coarse Al-Fe-Cr intermetallic compounds are crystallized and are detached by a surface grinding step or the like after Ni-P plating, which causes dishing in the surface of the Ni-P plating film.

Therefore, the Cr amount is 0.05 mass% or more and 0.35 mass% or less. From the viewpoint of sufficiently obtaining each of the above-described effects, the amount of Cr is preferably 0.10 mass% or more, more preferably 0.15 mass% or more, and further preferably 0.20 mass% or more. In addition, the amount of Cr is preferably 0.30 mass% or less from the viewpoint of further improving the surface smoothness of the Ni-P plating film.

(Cu: 0.10% by mass or less)

Cu is an element effective for improving Ni — P plating properties of the green body. Cu is uniformly dissolved in the base material, and in the zincate treatment of the pre-plating treatment, it has an effect of uniformly and finely precipitating Zn ions in the zincate bath on the surface of the base material (more specifically, the substrate). In other words, by containing Cu, the zincate film can be uniformly formed, and the formation of the build-up on the surface of the Ni — P plating film can be suppressed. However, when the Cu content is higher than 0.10 mass%, Cu precipitates in the grain boundaries, so that the grain boundaries are overetched to cause dishing and a large amount of surface nodules of the Ni — P plating film are generated in the acid etching treatment before the plating treatment.

Therefore, the Cu content is 0.10 mass% or less. Further, the Cu content is preferably 0.05 mass% or less from the viewpoint of further improving the surface smoothness of the Ni — P plating film. From the viewpoint of sufficiently obtaining the above-described effects, the amount of Cu is preferably 0.01 mass% or more, more preferably 0.03 mass% or more, and still more preferably 0.04 mass% or more.

(Zn: 0.40 mass% or less)

Zn is an element effective for improving the Ni-P plating property of the green body, similarly to C. Zn is uniformly dissolved in the green body, and in the zincate treatment of the pre-plating treatment, Zn ions in the zincate bath are uniformly and finely precipitated on the surface of the green body (more specifically, the substrate). In other words, by containing Zn, the zincate film can be uniformly formed, and the formation of the build-up on the surface of the Ni — P plating film can be suppressed. Further, Zn is uniformly precipitated in the green body with an increase in the amount of Zn, and tends to become an etching start point and a Zn ion precipitation point in zincate treatment in the acid etching treatment of the pre-plating treatment performed on the substrate. Therefore, the inclusion of Zn can exert an effect of suppressing the level difference due to the crystal grains. However, if the amount of Zn is more than 0.40 mass%, the precipitation nuclei of Zn increase, and accordingly, pits formed in the acid etching treatment performed as the pre-plating treatment also increase. Therefore, when the Zn content is more than 0.40 mass%, the smoothness of the Ni-P plating film surface is lowered. In addition, when the amount of Zn is more than 0.40 mass%, an Al-Mg-Zn-based intermetallic compound precipitates in grain boundaries, so that the grain boundaries are overetched in the acid etching treatment performed as the pretreatment for plating, and a large amount of nodules occur on the surface of the Ni-P plating film. When the amount of Zn is more than 0.40 mass%, the Al-Mg-Zn based intermetallic compound is also dissolved to form pits, which remain after plating.

Therefore, the amount of Zn is 0.40 mass% or less. In addition, the amount of Zn is preferably 0.33 mass% or less, more preferably 0.25 mass% or less, from the viewpoint of further improving the surface smoothness of the Ni-P plating film. From the viewpoint of sufficiently obtaining each of the above effects, the amount of Zn is preferably 0.01 mass% or more, more preferably 0.05 mass% or more, and still more preferably 0.10 mass% or more.

(Mn: less than 0.10 mass% (including 0 mass%))

Mn decreases the grinding rate in mirror finishing or the like of a green body with an increase in the addition amount. If the Mn content is 0.10 mass% or more, the grinding rate decreases, and the grindability decreases.

Therefore, the Mn content is less than 0.10 mass%. From the viewpoint of further improving the grindability, the Mn content is preferably 0.06% by mass or less, more preferably 0.03% by mass or less, and still more preferably 0% by mass. When the amount of Mn is set to the lower limit, it may be 0.0001% by mass.

(Fe: 0.025% by mass or less)

Fe is usually mixed into the Al alloy as an inevitable impurity in the raw material metal, and the Al — Fe intermetallic compound is crystallized in the casting step. If the Fe content is more than 0.025 mass%, the Al-Fe intermetallic compound may be detached from the surface of the green body to form pits in mirror processing such as cutting and grinding in the production of a substrate. Further, the Al-Fe intermetallic compound is dissolved by the acid etching treatment to form pits. The pits formed in this manner may reduce the surface smoothness of the plating film formed by the plating treatment.

Accordingly, the amount of Fe is 0.025 mass% or less. From the viewpoint of reducing the Al — Fe intermetallic compound content, the Fe content is preferably 0.022 mass% or less, and more preferably 0.017 mass% or less.

As described above, Fe is mixed into the Al alloy as an inevitable impurity in the raw material metal, and it is very difficult to achieve 0 mass%. It is not realistic to use a high-purity metal material in order to reduce the Fe content to less than 0.005 mass%, because the cost is very high. Although the Fe content is preferably 0 mass%, if it is in the range of 0.005 mass% or more and 0.025 mass% or less, the effect of improving the grindability and yield strength can be expected, and the effect of refining the recrystallized grains to improve the homogeneity of the zincate treatment can be expected. Therefore, when the lower limit is set to the Fe amount from the viewpoint of cost and the viewpoint of obtaining these effects, the Fe amount can be 0.005 mass% and can be 0.010 mass%.

Fe can be positively contained as long as it is 0.025 mass% or less.

(Si: 0.025 mass% or less)

Si is usually mixed into an Al alloy as an inevitable impurity in a raw material metal, and in a step of casting an ingot of the Al alloy, or the like, an Mg — Si based intermetallic compound is generated on the ingot of the Al alloy and the plate surface. When the amount of Si is more than 0.025 mass%, the Mg-Si intermetallic compound may be detached from the surface of the green body to form pits in mirror processing such as cutting and grinding in the production of a substrate. Further, the Mg — Si intermetallic compound is dissolved by the acid etching treatment before the plating treatment, and pits are formed. That is, if the Si content is higher than 0.025 mass%, the number of pits in the plated surface increases (in other words, the surface defects increase). Such a situation can be avoided by setting the Si content to 0.025 mass% or less.

Therefore, the Si content is 0.025 mass% or less. From the viewpoint of reducing the Mg — Si based intermetallic compound, the Si amount is preferably 0.020% by mass or less, and more preferably 0.015% by mass or less.

Si is a preferable component when not contained, but as described above, it is mixed into the Al alloy as an inevitable impurity in the raw material metal, and it is very difficult to achieve 0 mass%. In order to reduce the Si content to less than 0.005 mass%, it is necessary to use a high-purity raw material metal, and this is not practical because of the extremely high cost. Therefore, the Si content is 0.025 mass% or less, but from the viewpoint of cost, when the lower limit is set to the Si content, it can be 0.005 mass% and can be 0.008 mass%.

If Si is 0.025 mass% or less, Si can be positively contained.

(the balance being Al and unavoidable impurities)

The basic components of the chemical composition constituting the green body of the present embodiment are as described above, and the balance is Al and inevitable impurities. The inevitable impurities are those inevitably mixed in during the dissolution of the material, and are contained within a range not impairing the characteristics of the green body. Examples of the inevitable impurities include Ni, Ti, Na, Pb, Be, Ca, Zr, V, and B. The Cu, Zn, Mn, Fe, and Si may be contained as inevitable impurities.

The effect of the present invention is not impaired if the content of these unavoidable impurities is 0.005% by mass or less, and the total content is 0.015% by mass or less. Therefore, in the present invention, unavoidable impurities may be contained within a range not impairing the effects of the present invention, and the effects of the present invention are not impaired by the active addition of the impurities within a range not impairing the effects of the present invention (in short, these aspects are also included in the technical scope of the present invention).

The chemical composition of the green body of the present embodiment can be adjusted by appropriately adjusting the amount of elements added when melting the Al alloy, for example. The adjustment (limitation) of the content of the inevitable impurities can be performed by, for example, using a raw material metal refined by a three-layer electrolytic method or removing the raw material metal by a segregation method.

(maximum Length of Mg-Si intermetallic compound: 3 μm or less)

On the Mg-Si based intermetallic compound, Ni-P plating film cannot grow, and Ni-P plating film growing from the periphery thereof covers the intermetallic compound. Therefore, voids remaining in the Ni — P plating solution or the like are formed at the interface between the Ni — P plating film and the aluminum alloy substrate, and the surface of the Ni — P plating film is foamed due to heating or the like during magnetic film sputtering performed after the Ni — P plating treatment, thereby deteriorating smoothness. This phenomenon is particularly remarkable in the presence of coarse Mg — Si-based intermetallic compounds having a maximum length of more than 3 μm. In addition, coarse Mg-Si intermetallic compounds having a maximum length of more than 3 μm reduce the grinding rate of mirror finishing or the like of the green body.

Therefore, the maximum length of the Mg-Si intermetallic compound is 3 μm or less. The maximum length of the Mg-Si intermetallic compound is preferably 2 μm or less from the viewpoint of improving the smoothness and grindability of the Ni-P plating film surface. The smaller the maximum length of the Mg-Si intermetallic compound is, the more preferable, and the lower limit is not particularly limited, but is, for example, 0.5. mu.m.

The maximum length of the Mg — Si intermetallic compound can be controlled by the Si content, the condition (particularly, temperature) of the homogenization heat treatment, and the time from the end of the homogenization heat treatment to the end of the hot rolling. The same applies to the maximum length of the Mg-Si intermetallic compound of the substrate described later.

The maximum length of the Mg — Si intermetallic compound can be measured by the following method.

For example, first, the surface of a green body is cut with a diamond turning tool to be a mirror surface, and the mirror surface is photographed at a magnification of 1000 times using SEM (JSM-5500 manufactured by Japan electronic division) and particle analysis software (disc surface inspection software Ver.2.0)Take 20 visual fields (total 0.2 mm) on the surface²) And obtaining a COMPO image (group imaging). The threshold value was set at the gray base portion, and the portion blackened from the base portion (mother phase) was regarded as the Mg — Si intermetallic compound, and the absolute maximum length of each Mg — Si intermetallic compound (the maximum value of the distance between arbitrary 2 points on the contour line of the particle) was measured. Then, of the absolute maximum lengths of the respective Mg — Si based intermetallic compounds obtained, the maximum length is defined as "the maximum length of the Mg — Si based intermetallic compound".

(yield strength: 140MPa or more)

And performing correction annealing on the blank in the manufacturing process. The yield strength of the blank of the present embodiment produced by correction annealing is preferably 140MPa or more. The condition for the correction annealing is, for example, a condition of holding at 300 to 400 ℃ for 2 to 7 hours.

By setting the yield strength of the green body to 140MPa or more, sufficient impact resistance and deformation preventing effect at the time of handling can be obtained even when the thickness is reduced to about 0.8mm or less. From the viewpoint of further improving the impact resistance, the yield strength of the green body is preferably 143MPa or more, more preferably 155MPa or more, and still more preferably 160MPa or more. The upper limit of the yield strength is not particularly limited, and is, for example, 220 MPa.

The yield strength of the blank can be controlled by the contents of Mg and Cr. The same applies to the yield strength of the substrate described later.

Mechanical properties such as yield strength can be measured, for example, according to JIS Z2241: 2011A test piece is made of a green body or a substrate, and a tensile test of a metal material is performed.

[ substrate ]

The substrate of the present embodiment is manufactured by performing cutting (end face machining) on an end face of the green body of the present embodiment and performing grinding (mirror finishing) on a surface (main surface).

Also, the substrate is also referred to as a polishing substrate.

The substrate of the present embodiment has the same chemical composition and structure as the green body of the present embodiment. Therefore, the Ni — P plating film has mechanical properties required as a base sheet, is not easily strained during mounting and demounting of the substrate, has sufficient impact resistance to the extent that the substrate is not deformed by impact at the time of falling even when the substrate is thinned, and has excellent surface smoothness of the Ni — P plating film. Therefore, the substrate of the present embodiment can be applied to, for example, a 3.5-inch HDD. The substrate of the present embodiment, which has excellent impact resistance and a preferable surface smoothness of the Ni — P plating film, exhibits the same excellent characteristics when applied to, for example, a mobile 2.5-inch HDD (as does the blank).

The ranges of the chemical composition, yield strength and intermetallic compound of the substrate are the same as those of the green body.

[ method for producing blank ]

Next, an example of the method for producing a green body according to the present embodiment will be described.

The blank of the present embodiment can be manufactured by a manufacturing method and a manufacturing apparatus under normal conditions for manufacturing a magnetic disk substrate, except for some conditions. For example, the blank can be manufactured by a manufacturing method comprising the following steps in order: a casting step of melting the Al alloy of the chemical composition and casting an ingot adjusted to the chemical composition; a homogenization heat treatment step of performing homogenization heat treatment on the cast ingot; a hot rolling step of hot rolling the ingot subjected to the homogenization heat treatment to obtain a hot rolled sheet; a cold rolling step of cold rolling the hot-rolled sheet to obtain a cold-rolled sheet; a blanking step of blanking an aluminum alloy sheet obtained by cold rolling into a circular shape; and a correction annealing step of performing correction annealing on the punched substrate. If necessary, intermediate annealing may be performed before or during the cold rolling step.

Hereinafter, each step will be described in detail.

(casting step)

In the casting step, the raw material is melted and cast by a known casting method. When melting the Al alloy in the casting step, it is preferable to perform dehydrogenation by blowing an inert gas such as argon (Ar) into the molten metal. Further, it is preferable to produce an ingot at a casting speed of 30 to 80 mm/min. The casting temperature is preferably 680 to 720 ℃.

(homogenizing Heat treatment Process)

In the homogenizing heat treatment step, the cast piece of the Al alloy is subjected to surface cutting, and then, for example, at 500 to 550 ℃ for 1 to 20 hours. When the homogenization heat treatment is performed under such conditions, Mg can be made to be present₂An Mg-Si intermetallic compound such as Si is sufficiently dissolved in a solid state. If the temperature of the homogenization heat treatment is less than 500 ℃, the Mg-Si based intermetallic compound coarsens. On the other hand, if the temperature of the homogenization heat treatment is higher than 550 ℃, the surface of the ingot is melted. The time for the homogenization heat treatment is not particularly limited, but is more preferably 4 hours or more. The amount of surface cutting can be suitably changed in consideration of the degree of segregation, but the amount is preferably in the range of 3 to 20mm per surface, for example.

(Hot Rolling Process)

In the hot rolling step, the hot rolling start temperature is set to 540 ℃ or less, and the time from the end of the homogenization heat treatment (when taken out of the soaking furnace) to the end of the hot rolling is set to 30 minutes or less. When hot rolling is performed under such conditions, Mg can be avoided by the end of hot rolling₂The Mg-Si intermetallic compounds such as Si are coarsened or precipitated.

If the hot rolling start temperature is higher than 540 ℃, cracks occur in the hot rolling. From the viewpoint of further suppressing the occurrence of cracks in hot rolling, the hot rolling start temperature is preferably 530 ℃ or lower. When the time from the end of the homogenizing heat treatment to the end of the hot rolling exceeds 30 minutes, the Mg — Si intermetallic compound is coarsened. The time from the end of the homogenization heat treatment to the end of the hot rolling is preferably 10 minutes or less, and more preferably 5 minutes or less, from the viewpoint of further suppressing the coarsening of the Mg — Si based intermetallic compound.

When the hot rolling completion temperature is lower than 300 ℃, luders band is generated in the subsequent cold rolling step. The luders tape does not remain on the surface after grinding, and therefore does not impair the function as a magnetic disk, but detracts from the appearance of the Al alloy sheet and blank before grinding. Therefore, in order to prevent this, the hot rolling end temperature is preferably 300 ℃ or higher.

(Cold Rolling Process)

In the cold rolling step, the rolling is performed so as to achieve a target thickness of the blank. Specific examples of the plate thickness include 0.5 to 1.3 mm. If necessary, intermediate annealing may be performed before or during the cold rolling.

(Blanking step)

In the punching step, the cold-rolled plate material is subjected to hardening and tempering as necessary, and then, for example, an aluminum alloy plate is punched into a desired shape so as to be applicable to a 3.5-inch HDD substrate or a 2.5-inch HDD substrate.

(corrective annealing step)

In the correction annealing step, several tens of disc-shaped plate materials are stacked between separators having high flatness, and annealed while being entirely pressed. Generally, a plate material separated one by one after the pressure annealing is called a green body.

The condition for the correction annealing is, for example, a condition of holding at 300 to 400 ℃ for 2 to 7 hours.

[ method for producing substrate ]

The substrate of the present embodiment can be manufactured by, for example, a manufacturing method in which cutting (end face machining) for cutting an end face of a blank and grinding (mirror finishing) for grinding a surface (principal face) of the blank are performed.

Magnetic disk and method for producing the same

In the magnetic disk manufacturing method, first, the surface of a substrate is subjected to acid etching treatment to form an electroless Ni — P plating film, and then the surface is polished (also, the substrate on which the electroless Ni — P plating film is formed is also referred to as a plating substrate). Next, on the surface of this substrate, an under film for improving magnetic properties, a magnetic film made of a Co-based alloy, a protective film made of C (carbon) for protecting the magnetic film, and the like are formed by sputtering or the like, whereby a magnetic disk can be manufactured.

The formation of the electroless Ni — P plating film, the primary coating, the magnetic coating, and the protective coating can be performed under conditions generally used in the production of a magnetic disk.

In the production of the green sheet and the base sheet, for example, the production conditions described in japanese patent No. 3471557 and japanese patent No. 5199714 can be referred to.

As described above, the main difference between the blank and the substrate in the present embodiment is whether or not grinding (mirror finishing) is performed. Thus, for a yield strength measurement made of the substrate, the intermetallic measurement can be directly considered as a green body measurement and vice versa.

(other steps)

As described above, the method for manufacturing a blank, a substrate, and a magnetic disk according to the present embodiment may include other steps between or before the steps, as long as the steps are not adversely affected.

[ other embodiments ]

The present invention is applicable to a laminate material including a core material and a skin material provided on at least one surface of the core material.

Blank and substrate (other embodiments)

The blank and the base sheet according to another embodiment are configured to have a laminated material including a "core material" and a "skin material" provided on at least one surface of the core material.

When the green sheet and the base sheet are a laminate, it is preferable that the laminate as a whole satisfies the requirement of "yield strength" of the above-mentioned single-layer material.

(leather material)

The skin material of the green body and the substrate according to another embodiment preferably satisfies the requirements of "composition of each component" and "maximum length of Mg — Si based intermetallic compound on the surface" of the single layer material.

(core material)

The core material of the green body and the substrate according to another embodiment is not particularly limited, but examples thereof include Al-Mn system alloys, Al-Ni system alloys, Al-Fe system alloys, Al-Mn-Ni system alloys, Al-Ni-Mn system alloys, Al-Mn-Fe system alloys, Al-Fe-Mn system alloys, Al-Ni-Fe system alloys, Al-Fe-Ni system alloys, Al-Mn-Ni-Fe system alloys, Al-Mn-Fe-Ni system alloys, Al-Ni-Mn-Fe system alloys, Al-Fe-Mn-Ni system alloys, and Al-Fe-Ni-Mn-Mn system alloys.

Specifically, the core material contains Mn: 0.1 to 3.0 mass% of Ni: 0.1 to 2.0 mass% inclusive, Fe: 0.1 to 2.0 mass% of Si: 0.1 to 15 mass%, Cr: 0.01 to 2.0 mass% inclusive, and the balance of Al and unavoidable impurities.

The core material may contain Fe, Mn or Ni alone, may contain two kinds of Fe and Mn, Mn and Ni, or Ni and Fe, or may contain all of Fe, Mn and Ni, and the upper limit of the total content thereof is not particularly limited as long as it is 5 mass%.

In addition, the alloy may further contain Mg in a range of 1.0 mass% or more and 3.0 mass% or less.

(balance of core Material: Al and unavoidable impurities)

The balance of the core material of the green body and the substrate according to the other embodiment is Al and inevitable impurities. Examples of the inevitable impurities include Cu, Zn, Ti, Na, Pb, Be, Ca, Zr, V, and B. The Ni, Mn, Fe, Si, and Cr may be contained as inevitable impurities.

The effect of the present invention is not impaired if the content of these unavoidable impurities is 0.005% by mass or less, and the total content is 0.015% by mass or less. Therefore, in the present invention, unavoidable impurities may be contained within a range not impairing the effects of the present invention, and when the impurities are added positively within a range not impairing the effects of the present invention, the effects of the present invention are not impaired (in other words, these aspects are included in the technical scope of the present invention).

(coating ratio, etc.)

The thickness of the green sheet and the base sheet in the other embodiments is not particularly limited, but may be 0.5 to 1.3mm as in the case of the single-layer material. In addition, the coating ratio of the skin materials of the green sheet and the base sheet (the ratio of the thickness of each skin material when the thickness of the laminate is 100%) in another embodiment may be 3 to 50%, and preferably 5 to 30%.

[ method for producing blank (other embodiment) ]

The blank according to the other embodiments can be produced by a production method and a production facility under normal conditions for producing a magnetic disk substrate, as in the case of the single-layer material, and also in the case of the laminated material, except for some conditions.

For example, a leather material is produced by a production method including the following steps in this order: a casting step of melting the Al alloy having the chemical composition to produce an ingot adjusted to the chemical composition; a homogenization heat treatment step of performing homogenization heat treatment on the cast ingot; and a hot rolling step of hot rolling the ingot subjected to the homogenization heat treatment to obtain a hot rolled sheet.

Then, the core material is manufactured by a manufacturing method sequentially comprising the following steps: a casting step of melting the Al alloy of the chemical composition and casting an ingot adjusted to the chemical composition; a homogenizing heat treatment step of performing homogenizing heat treatment on the cast ingot.

After the core material and the skin material are manufactured, a blank (laminate) can be manufactured by a manufacturing method including the following steps in this order: an overlapping step of overlapping the core material and the skin material; a homogenizing heat treatment step of performing a homogenizing heat treatment on the laminate; a hot rolling step of hot rolling the laminate; a cold rolling step of rolling the laminated material to a desired thickness; a blanking step of blanking the laminated material obtained by the cold rolling into a circular shape; and a correction annealing step of performing correction annealing on the punched laminated material.

The conditions of the respective steps are as follows.

In order to control the maximum length of the Mg — Si intermetallic compound on the surface, the casting step, the homogenization heat treatment step, and the hot rolling step of the cladding are performed so as to satisfy the conditions (particularly, the temperature and time of the homogenization heat treatment, and the time from the end of the homogenization heat treatment to the end of the hot rolling) indicated in the "casting step", "homogenization heat treatment step", and "heat treatment step" of the single-layer material.

The core material casting step and the homogenization heat treatment step may be performed so as to satisfy the conditions indicated in the "casting step" and the "homogenization heat treatment step" of the single-layer material.

The overlapping method in the overlapping step is a conventionally known method, and for example, a method of binding a belt to both ends of the core member and the skin member, a method of welding and fixing, and the like can be cited.

The homogenization heat treatment of the laminate may be performed, for example, at 500 to 550 ℃ for 1 to 20 hours.

The hot rolling of the laminate may be carried out, for example, under conditions of a start temperature of 510 to 540 ℃ and a time from the end of the homogenization heat treatment to the end of the hot rolling of 30 minutes or less.

The cold rolling of the laminate may be performed, for example, so that the thickness of the laminate is 0.5 to 1.3 mm.

The laminated material punching step may be performed under conditions satisfying the conditions indicated in the "punching step" of the single-layer material. The correction annealing step of the laminated material may be performed under conditions satisfying the conditions described in the "correction annealing step" of the single-layer material, but the holding time may be as long as 7 to 9 hours.

In addition, as the method for manufacturing each of the core material and the skin material, a slicing and milling method as described in paragraph 0048 of japanese patent No. 5271094 may be applied. More specifically, an Al alloy for core material and an Al alloy for sheath material were respectively melt-cast, and the obtained ingots were subjected to surface cutting and homogenization heat treatment to produce an ingot for sheath material and an ingot for core material (core material), respectively. Then, the skin material ingot was further subjected to surface cutting, homogenized heat treatment, and then sliced to a desired thickness to manufacture the skin material ingot. In this case, it is necessary to control the homogenization heat treatment conditions and hot rolling conditions after the overlapping step so as to appropriately satisfy the conditions indicated by the above-described single-layer material.

Then, the method of manufacturing the substrate and the magnetic disk using the green sheet (laminated sheet) is the same as the case of the single-layer sheet.

[ examples ] A method for producing a compound

Next, the contents of the present invention will be specifically described with reference to examples having the effects of the present invention and comparative examples not shown.

Example 1: single layer material)

(trial production of DC casting: preparation of test Material)

First, the materials were melted, and the compositions thereof were adjusted so as to have chemical compositions shown in Nos. 1 to 3 of Table 1, and ingots were DC cast. The conditions for DC casting were such that the casting speed was 80mm/min, the casting temperature was 720 ℃ (holding furnace temperature, strictly speaking, 700 to 720 ℃ for cooling when passing through a launder), and the ingot size was 150mm in height, 400mm in width, and 400mm in length.

Next, the obtained ingot was cut into pieces of 40mm in height, 150mm in width and 200mm in length, and both surfaces were subjected to surface cutting of 2mm, respectively, and then subjected to homogenization heat treatment under the conditions shown in Table 1.

Then, the materials No.1 and No.3 were hot-rolled with the time from the end of the homogenization heat treatment (the time of taking out from the soaking furnace) to the end of the hot rolling being 3 minutes (the starting temperature: 520 ℃ C., the finish rolling thickness: 5 mm).

On the other hand, the material No.2 was held in a furnace at 450 ℃ after the homogenization heat treatment for 50 minutes in order to simulate long-time hot rolling, and was taken out and hot rolled (start temperature 450 ℃ C., finish rolling thickness 5 mm). Specifically, the time from the end of the homogenization heat treatment to the end of the hot rolling was 53 minutes.

Subsequently, the obtained hot-rolled sheet is subjected to cold rolling. The cold rolling was performed by passing the steel sheet a plurality of times so that the material temperature did not exceed 100 ℃ and the steel sheet had a thickness of 0.8 mm.

The cold-rolled sheet was then punched into a 3.5 inch circular ring shape (about 95mm outer diameter and about 25mm inner diameter), and stacked for straightening annealing. The straightening annealing was performed at 320 ℃ for 3 hours.

Thereafter, the sheets were peeled off to produce blanks (0.8 mm in thickness) for 3.5-inch HDDs of Nos. 1 to 3. Subsequently, end face machining of each blank is performed. Then, the surface (both surfaces) of the green body was ground to 10 μm on one side (mirror finish) with a PVA grindstone (4000. ang. manufactured by Nippon Denshoku Co., Ltd.) to produce substrates (0.8 mm in thickness) of No.1 to 3.

(trial production by book-type mold: preparation of test Material)

First, the material was melted, and the composition was adjusted so that the chemical composition was as shown in nos. 11 to 15 of table 2, and an ingot (book mold) was die-cast. The dimensions of the mold were 50mm in height, 145mm in width, 200mm in length, and the casting temperature was 720 ℃.

Then, 2mm surface cutting was performed on both surfaces of the obtained ingot, and homogenization heat treatment was performed under the conditions shown in table 2.

Thereafter, the time from the end of the homogenization heat treatment (when taken out from the soaking furnace) to the end of the hot rolling was set to 3 minutes, and the material after the homogenization heat treatment was hot rolled (starting temperature 520 ℃ C., finish rolling thickness 5 mm).

Subsequently, the obtained hot-rolled sheet is subjected to cold rolling. The cold rolling was performed by passing the steel sheet a plurality of times so that the material temperature did not exceed 100 ℃ and the steel sheet had a thickness of 1.3 mm.

The cold-rolled sheet was then punched into a 3.5 inch circular ring shape (about 95mm outer diameter and about 25mm inner diameter), and stacked for correction annealing. The straightening annealing was performed at 320 ℃ for 3 hours.

Thereafter, the sheets were peeled off to produce blanks (1.3 mm in thickness) for 3.5-inch HDDs of Nos. 11 to 15. Subsequently, end face machining of each blank is performed. Then, the surface (both surfaces) of the green body was ground to 10 μm on one side (mirror finish) with a PVA grindstone (4000. TM. manufactured by Nippon Denshoku Co., Ltd.) to produce substrates (1.3 mm in thickness) of Nos. 11 to 15.

The maximum length, yield strength and impact resistance of the Mg-Si intermetallic compound on the surface of the plate were evaluated using the produced blanks or substrates of Nos. 1 to 3 and 11 to 15. These evaluations were performed in the following manner.

Maximum Length of [ 1 ] Mg-Si based intermetallic Compound

The maximum length (. mu.m) of the Mg-Si based intermetallic compound on the surface of the blank of Nos. 1 to 3 was measured by the following method.

First, the surface of a green body was cut with a diamond turning tool to be a mirror surface, and 20 visual fields (total 0.2 mm) were photographed at a magnification of 1000 times using SEM (JSM-5500 manufactured by Japan electronic division) and particle analysis software (disc surface inspection software Ver.2.0) for the mirror surface²) And obtaining a COMPO image (group imaging). The threshold value was set at the gray base portion, and the portion blackened from the base portion (mother phase) was regarded as the Mg — Si intermetallic compound, and the absolute maximum length (maximum value of distance between arbitrary 2 points on the contour line of the particle) of each Mg — Si intermetallic compound was measured. Then, of the absolute maximum lengths of the respective Mg — Si based intermetallic compounds obtained, the maximum length is defined as "the maximum length of the Mg — Si based intermetallic compound".

If an Mg-Si based intermetallic compound having a maximum length of more than 3 μm is present on the surface of the substrate, the Ni-P plating film does not grow on this intermetallic compound, but the Ni-P plating film grown from the periphery thereof covers the intermetallic compound. As a result, voids such as Ni — P plating solution are formed at the interface between the Ni — P plating film and the substrate, and the surface of the Ni — P plating film is foamed due to heating during sputtering of the magnetic film after the Ni — P plating treatment, thereby deteriorating smoothness.

Therefore, it is estimated that the smoothness of the Ni-P plating film surface is excellent without the presence of the Mg-Si intermetallic compound having the maximum length exceeding 3 μm (3.00 μm), and the smoothness of the Ni-P plating film surface is judged to be acceptable (good). On the other hand, the presence of the Mg-Si intermetallic compound having the maximum length exceeding 3 μm (3.00 μm) is presumed to result in poor smoothness of the Ni-P plating film surface, and the smoothness of the Ni-P plating film surface is judged to be defective (X).

Further, it is presumed that the Ni-P plating film surface is excellent in smoothness because there is no Mg-Si intermetallic compound having a maximum length exceeding a predetermined value, and it is also found that the description based on Japanese patent No. 4490850 is appropriate.

(2) yield strength

Test pieces of JIS No. 13B were cut from the blanks of Nos. 1 to 3 and 11 to 15 so that the stretching direction was parallel to the rolling direction. Using the test piece, the test piece was measured in accordance with JIS Z2241: 2011(offset method: residual deformation method), a tensile test was conducted to determine a yield strength (0.2% yield strength). The drawing rate was 3mm/min (strain amount to 0.5%) and 20mm/min (strain amount to more than 0.5%).

Yield strength of 140MPa or more was judged as good (good), and those below 140MPa were judged as bad (X)

[ 3 ] impact resistance

The impact resistance was evaluated by using an impact resistance tester 1 shown in FIG. 1.

First, blanks No.1 to No.3 and No.11 to No. 15 were subjected to end face processing so as to have inner and outer diameters that could be mounted on HDD12 (HDD ST10000DM0004 manufactured by Seagate corporation) shown in FIG. 2. Then, the blank 11 after the end face processing was mounted on the HDD12 from which the disk was removed, to obtain a test piece 10 (mass: 470 g).

The method of mounting the blanks 11 on the HDD12 is to mount 1 blank each as a measurement target, and also to mount a total of 7 blanks (the same number as the number of disks mounted on the HDD 12) on the position of the HDD12 where the disks are mounted, and then to fix the blanks at 6 with screws S, as appropriate, by using a dummy blank.

When the total of 7 blanks 11 are mounted on the HDD12, no gap is formed between the blanks in the vertical direction, and therefore, the result is not affected regardless of whether the mounting position of the blank is the uppermost side, the vicinity of the center, or the lowermost side. In other words, it was confirmed that the mounting position of the blank to the HDD had no influence on the present result.

Thereafter, as shown in FIG. 1, the test piece 10 covered with the upper lid was fixed to the upper surface of an aluminum plate 3 (mass: 3935g, dimensions: width: 220 mm. times. length: 220 mm. times. thickness: 30mm) with a seal (not shown) via a spacer 4 (mass: 430 g).

The support rods 5 shown in fig. 1 are guide rods for directly dropping the aluminum plate 3 to which the test piece 10 is fixed, and holes for passing the support rods 5 are provided at 4 corners of the aluminum plate 3.

Then, in the impact resistance tester 1, the aluminum plate 3 to which the test body 10 was fixed was lifted up to a height position at which the lower surface of the aluminum plate 3 was 600mm from the upper surface of the aluminum block 2, and dropped. This fall schedule was then repeated 5 times.

Thereafter, the blank 11 was detached from the HDD12 of the test body 10, and the flatness of the surface of the blank 11 was measured.

Also, the upper and lower surfaces of the aluminum block 2 and the aluminum plate 3 are both subjected to surface cutting, and in the dropping operation, an impact between metals, which is caused by the lower surface of the aluminum plate 3 impacting the upper surface of the aluminum block 2, is applied to the blank 11 of the test body 10.

The flatness of the surface of the green body was measured by FT-17, NIDEK. Then, in the blanks (thickness: 0.8mm) of Nos. 1 to 3, when the change amount of the flatness before and after 5 times of the falling operation was 0.50 μm or less, the impact resistance was good (good), and when it was more than 0.50 μm, the impact resistance was not good (x). In addition, in the blanks (thickness 1.3mm) of Nos. 11 to 15, when the change amount of flatness before and after 5 times of falling operation was 0.12 μm or less, the impact resistance was good (good), and when it was more than 0.12 μm, the impact resistance was not good (x).

In the tables, the composition of the green body and the substrate, and the results of the measurement or evaluation in [ 1 ] to [ 3 ] are shown. The underline in the table indicates that the requirements specified in the present invention are not satisfied.

[ TABLE 1 ]

[ TABLE 2 ]

TABLE 2

The balance is Al and inevitable impurities.

(investigation of results: results of Table 1)

As shown in Table 1, since No.1 satisfied the requirements of the present invention, the smoothness, yield strength and impact resistance of the Ni-P plating film surface were all evaluated as acceptable.

On the other hand, in No.2, the time from the end of the homogenizing heat treatment to the end of the hot rolling was long, and coarse Mg-Si intermetallic compounds were generated, and the smoothness of the Ni-P plating film surface was poor.

Further, since No.3 contained a small amount of Mg, it was inferior in yield strength and impact resistance.

(investigation of results: results of Table 2)

As shown in Table 2, No.13 was judged to be acceptable in terms of yield strength and impact resistance.

On the other hand, samples Nos. 11, 12, 14 and 15 had poor yield strength and poor impact resistance because of their small Mg content.

(investigation of results: discussion of results in Table 2)

The results of Nos. 11 to 15 shown in Table 2 are obtained for clarifying the relationship between the "yield strength" and the "impact resistance" of the green body.

The graph shown in FIG. 3 plots the results of Nos. 11 to 15, with the value of yield strength (MPa) on the horizontal axis and the amount of change in flatness (μm) on the vertical axis. In the graph of fig. 3, when approximate lines are drawn with respect to nos. 11, 12, 14, and 15 in which the flatness changes reliably, the lines are broken lines as shown in fig. 3.

From the results of fig. 3, it is understood that if the yield strength of the green body is 140MPa (strictly 136MPa) or more, the amount of change in flatness is hardly changed, but if it is less than 140MPa, the amount of change in flatness becomes large in accordance with the decrease in yield strength. In other words, it is assumed that there is a critical point relating to the amount of change in flatness at the point that the yield strength of the green body is 140MP (strictly 136 MPa).

(investigation of results: reconfirmation of results in Table 1)

As a result of confirming again the results in table 1, nos. 1 and 2 having a yield strength of 140MPa or more (strictly speaking, 136MPa or more) can suppress the amount of change in flatness, and No.3 having a yield strength of less than 140MPa has a large amount of change in flatness.

Thus, it was confirmed that the results of Table 2 and FIG. 3 are also applicable to Nos. 1 to 3.

Although there was a difference in the amount of change in flatness between Nos. 1 to 3 and 11 to 15, this was considered to be a great influence of the plate thickness (0.8 mm for Nos. 1 to 3 and 1.3mm for Nos. 11 to 15).

From the above results, it was confirmed that the green sheet and the substrate of the present invention are excellent in impact resistance and smoothness of the Ni-P plated surface.

Example 2: laminate material

(preparation of test materials from book-type molds)

First, a material for a leather material was melted, and a mold casting (book mold) was performed to obtain an ingot having a chemical composition shown in No.21 of table 3 by adjusting the composition. The dimensions of the mold were 50mm in height, 145mm in width, 200mm in length, and the casting temperature was 720 ℃.

Next, both surfaces of the obtained ingot were subjected to 2mm surface cutting, respectively, and then to homogenization heat treatment under the conditions shown in Table 3.

Thereafter, the time from the end of the homogenization heat treatment (when taken out from the soaking furnace) to the end of the hot rolling was set to 3 minutes, and the material after the homogenization heat treatment was hot rolled (start temperature 540 ℃ C., finish rolling thickness 3 mm).

Further, the core material was melted, and the composition was adjusted to be Cr: 0.21 mass%, Cu: 0.17 mass%, Zn: 0.14 mass%, Mn: 2.0 mass%, Fe: 0.058 mass%, Si: 0.019 mass%, and the balance of Al and inevitable impurities, and a mold casting (book-type mold) ingot. The dimensions of the mold were 50mm in height, 145mm in width, 200mm in length, and the casting temperature was 720 ℃.

Next, both surfaces of the obtained ingot were subjected to 13mm surface cutting, respectively, and then to homogenization heat treatment at 540 ℃ for 4 hours.

Thereafter, a skin material (thickness: 3mm), a core material (thickness: 24mm) and a skin material (thickness: 3mm) were welded and fixed to each other to prepare a three-layer clad material.

Then, the clad material was charged into a furnace at 540 ℃, heated to 540 ℃, and then subjected to a homogenization heat treatment for 1 hour and 30 minutes, and then hot rolled (finish rolling thickness 3mm) with the time from the end of the homogenization heat treatment to the end of hot rolling being 3 minutes. Subsequently, the obtained hot-rolled sheet is subjected to cold rolling. The cold rolling was performed by passing the steel sheet a plurality of times so that the material temperature did not exceed 100 ℃ and the steel sheet had a thickness of 0.5 mm.

The thickness ratio of the sheath material, the core material, and the sheath material is approximately 10%: 80%: 10 percent.

The cold-rolled sheet was then punched into a 3.5 inch circular ring shape (about 95mm outer diameter and about 25mm inner diameter), and stacked together for straightening annealing. Also, the correction annealing was performed in such a manner that the temperature was maintained in the range of 260 ℃ to 320 ℃ for 8 hours.

Thereafter, the sheet was peeled off to produce a blank for a 3.5-inch HDD of No.21 (plate thickness: 0.5 mm).

Then, using the manufactured No.21 green body, the yield strength was evaluated in the same manner as in example 1.

In the table, the composition of the skin material of the green body and the results of the yield strength are shown. The underline in the table indicates that the requirements specified in the present invention are not satisfied.

[ TABLE 3 ]

TABLE 3

The balance is Al and inevitable impurities.

(investigation of results: results of Table 3)

As shown in Table 3, the skin material No.21 satisfies the requirements of the present invention, and therefore, it was qualified as a laminate for evaluation of yield strength.

Although the maximum length of the Mg — Si intermetallic compound on the surface of the skin material of No.21 is not shown, it is assumed that the maximum length is the same as that of No.1 because the requirements of the composition defined in the present invention are satisfied, the temperature and time for the homogenization heat treatment, and the time from the end of the homogenization heat treatment to the end of the hot rolling are preferable in the present invention as in No. 1.

While the present invention has been described in detail with reference to the embodiments and examples, the spirit of the present invention is not limited to the above description, and the scope of the claims should be construed based on the scope of the claims. It is needless to say that the contents of the present invention can be changed or modified based on the description.

Also, the present application is based on japanese patent application (japanese application 2019-047754) applied on 3/14/2019 and japanese patent application (japanese application 2020-002933) applied on 10/1/2020, the contents of which are incorporated by reference in the present application.

Description of the symbols

1 impact resistance tester

2 aluminum block

3 aluminum plate

4 shim

5 support rod

10 test body

11 blank

12 HDD

S screw