阅读说明：本技术 阻燃性镁合金及其制造方法 (Flame-retardant magnesium alloy and method for producing same ) 是由 家永裕一 野坂洋一 于 2020-02-04 设计创作，主要内容包括：本发明提供一种抑制在铸造时的合金熔解过程中发生熔融金属燃烧的阻燃性镁合金及其制造方法。通过制成包含特定量的特定元素且进一步包含特定量的稀土类元素(RE)的镁合金,在熔融金属的最表面形成致密、较薄、且不易开裂的稀土类元素(RE)的氧化膜。具体来说,制成一种阻燃性镁合金,其以质量％计,含有低于9.0％的Ca、0.5％以上且低于5.7％的Al、1.3％以下的Si、及0.4％以上且低于1.3％的稀土类元素,剩余部分由Mg及不可避免的杂质组成,并且,Al+8Ca≧20.5％。(The invention provides a flame-retardant magnesium alloy which can inhibit molten metal from burning in an alloy melting process during casting and a manufacturing method thereof. By forming a magnesium alloy containing a specific amount of a specific element and further containing a specific amount of a rare earth element (RE), a dense, thin oxide film of the rare earth element (RE) that is less likely to crack is formed on the outermost surface of the molten metal. Specifically, a flame-retardant magnesium alloy is produced, which contains, in mass%, less than 9.0% of Ca, 0.5% or more and less than 5.7% of Al, 1.3% or less of Si, and 0.4% or more and less than 1.3% of rare earth elements, with the remainder being Mg and unavoidable impurities, and with Al +8Ca ≧ 20.5%.)

1. A flame-retardant magnesium alloy which comprises, by mass%, less than 9.0% of Ca, 0.5% to 5.7% of Al, 1.3% or less of Si, and 0.4% to 1.3% of a rare earth element, with the remainder being Mg and unavoidable impurities,

Al+8Ca≧20.5％。

2. the flame-retardant magnesium alloy according to claim 1, wherein the composition ratio of Al to Ca, Al/Ca, is 1.7 or less.

3. A flame-retardant magnesium alloy which comprises, by mass%, less than 9.0% of Ca, 0.5% to 5.7% of Al, 1.3% or less of Si, and 0.4% to 1.3% of a rare earth element, with the remainder being Mg and unavoidable impurities,

with continuous (Mg, Al) in the form of a three-dimensional network₂A Ca phase.

4. A flame-retardant magnesium alloy which comprises, by mass%, less than 9.0% of Ca, 0.5% to 5.7% of Al, 1.3% or less of Si, and 0.4% to 1.3% of a rare earth element, with the remainder being Mg and unavoidable impurities,

the thermal conductivity is 80W/mK or more, and the tensile strength at 200 ℃ is 170MPa or more.

5. The flame-retardant magnesium alloy according to any one of claims 1 to 4, wherein a Ca-Mg-Si based compound phase is contained in the Mg parent phase.

6. The flame-retardant magnesium alloy according to any one of claims 1 to 5, wherein the Mg purity of the Mg parent phase is 98.0% or more.

7. The flame-retardant magnesium alloy according to any one of claims 1 to 6, wherein the rare earth element is a misch metal.

8. A method for producing a flame-retardant magnesium alloy according to any one of claims 1 to 7, comprising:

cooling step to less than 10³The molten metal material is cooled at a speed of K/sec.

9. A method for producing a flame-retardant magnesium alloy according to any one of claims 1 to 7, comprising:

a crystallization step of cooling the molten metal material to form a three-dimensional network of continuous (Mg, Al)₂The Ca phase and the Mg parent phase including the Ca-Mg-Si compound phase are crystallized.

10. The method for producing a flame-retardant magnesium alloy according to claim 8 or 9, further comprising: a heat treatment step of performing heat treatment at 150-500 ℃.

Technical Field

The invention relates to a flame-retardant magnesium alloy and a manufacturing method thereof. More particularly, the present invention relates to a flame-retardant magnesium alloy having ablation resistance while suppressing the occurrence of molten metal burning, and a method for producing the same.

Background

Since magnesium is lighter in weight than iron or aluminum, it is being studied as a lightweight alternative material to replace members composed of a steel material or an aluminum alloy material. As typical magnesium alloys, for example, Mg — Al — Zn — Mn alloys containing 9 wt% of aluminum, 1 wt% of zinc, and 0.3 wt% of manganese (AZ91D alloys), and Mg — Al — Mn alloys containing 6 wt% of aluminum and 0.3 wt% of manganese (AM60B alloys) are known.

However, since the strength of magnesium alloys is reduced at high temperatures, there is a problem in expanding to applications requiring heat-resistant strength. In contrast, magnesium alloys with improved heat resistance by adding rare earth elements (RE) have been proposed.

Patent document 1 discloses the following magnesium alloy: the alloy contains 2-10 wt% of aluminum, 1.4-10 wt% of calcium, and the ratio of Ca/Al is more than 0.7, and also contains less than 2 wt% of zinc, manganese, zirconium and silicon, and also contains less than 4 wt% of at least one element selected from rare earth elements (such as yttrium, neodymium, lanthanum, cerium and mixed rare earth metals).

Further, patent document 2 discloses the following magnesium alloy: contains 1.5 to 10 wt% of aluminum, 2.5 wt% or less of rare earth elements (RE), and 0.2 to 5.5 wt% of calcium.

According to patent documents 1 and 2, by adding a rare earth element (RE) to the magnesium alloy, a magnesium alloy having sufficient strength even at high temperatures and excellent heat distortion resistance in a pressurized part at high temperatures can be obtained.

However, in the process of melting the magnesium alloy during casting, the molten metal may burn, which may cause a serious problem in terms of safety.

[ Prior Art document ]

(patent document)

Patent document 1: japanese laid-open patent publication No. 6-025790

Patent document 2: japanese laid-open patent publication No. 7-278717

Disclosure of Invention

[ problems to be solved by the invention ]

The present invention has been made in view of the above circumstances, and an object thereof is to provide a flame-retardant magnesium alloy that suppresses burning of molten metal during melting of the alloy at the time of casting, and a method for producing the same.

[ means for solving problems ]

The present inventors have made an effort to study the mechanism of occurrence of molten metal combustion. Moreover, it is considered that the molten metal burning is related to an oxide film formed on the surface of the molten metal. Specifically, a magnesium oxide (MgO) layer is formed on the surface of the molten magnesium alloy, which is a molten metal, after melting. Since the MgO film is porous, oxygen passes through the formed MgO film and reaches the magnesium metal present inside. Therefore, even when the molten metal of a general magnesium alloy is left alone, the molten metal may burn due to oxygen reaching the inside.

Next, in the case of a calcium-containing magnesium alloy to which flame retardancy is imparted, a layered oxide film is formed by forming a magnesium oxide (MgO) layer on the surface of the molten metal and then layering a calcium oxide (CaO) layer on the magnesium oxide (MgO) layer. Since the CaO film as the outermost layer has a function of blocking oxygen, combustion can be suppressed in a state where the molten metal is left standing.

However, the CaO film present on the surface of the molten metal is thick and easily cracked, although it is dense. Therefore, when the molten metal is stirred, cracks are generated in the CaO film existing on the outermost surface, and oxygen passing through the cracks of the CaO film passes through the porous MgO film and reaches the magnesium metal existing inside. As a result, it is considered that molten metal combustion occurs.

Therefore, the present inventors have studied the following methods: not only the molten metal in a static state but also a film which is less likely to crack is formed even when the molten metal is stirred. As a result, the present inventors have found that when a magnesium alloy containing a specific amount of a specific element and further containing a specific amount of a rare earth element (RE) is prepared, an oxide film of the rare earth element (RE) can be formed on the outermost surface of the molten metal, and the oxide film of the rare earth element (RE) is dense, thin, and less likely to crack, and therefore cracking of the oxide film can be suppressed even when the molten metal is stirred, thereby completing the present invention.

That is, the present invention is a flame-retardant magnesium alloy containing, in mass%, less than 9.0% of Ca, 0.5% or more and less than 5.7% of Al, 1.3% or less of Si, and 0.4% or more and less than 1.3% of rare earth elements, with the remainder being Mg and inevitable impurities, and not less than 20.5% of Al +8 Ca.

In the flame-retardant magnesium alloy of the present invention, the composition ratio of Al to Ca, Al/Ca, may be 1.7 or less.

The present invention is also a flame-retardant magnesium alloy which contains, by mass%, less than 9.0% of Ca, 0.5% to less than 5.7% of Al, 1.3% or less of Si, and 0.4% to less than 1.3% of rare earth elements, with the remainder being Mg and unavoidable impurities, and which has a three-dimensional network-continuous (Mg, Al)₂A Ca phase.

Still another aspect of the present invention is a flame-retardant magnesium alloy containing, in mass%, less than 9.0% of Ca, 0.5% to less than 5.7% of Al, 1.3% or less of Si, and 0.4% to less than 1.3% of rare earth elements, with the remainder being Mg and unavoidable impurities, and having a thermal conductivity of 80W/m · K or more and a tensile strength at 200 ℃ of 170MPa or more.

The flame-retardant magnesium alloy of the present invention may have a Ca-Mg-Si compound phase in the Mg matrix phase.

In the flame-retardant magnesium alloy of the present invention, the Mg purity of the Mg parent phase may be 98.0% or more.

The rare earth element may be a misch metal.

The present invention is also a method for producing a flame-retardant magnesium alloy, which is the method for producing a flame-retardant magnesium alloy, and includes: cooling step to less than 10³The molten metal material is cooled at a speed of K/sec.

The present invention is also a method for producing a flame-retardant magnesium alloy, which is the method for producing a flame-retardant magnesium alloy, and includes: a crystallization step of cooling the molten metal material to form a three-dimensional network of continuous (Mg, Al)₂The Ca phase and the Mg parent phase including the Ca-Mg-Si compound phase are crystallized.

The method for manufacturing the flame-retardant magnesium alloy of the present invention may further comprise: a heat treatment step of performing heat treatment at 150-500 ℃.

(Effect of the invention)

Since the flame-retardant magnesium alloy of the present invention has an oxide film of a rare earth element (RE) formed on the outermost surface of the molten metal, the flame-retardant magnesium alloy can suppress burning of the molten metal not only in the static state but also when the molten metal is stirred.

Further, since the cast product cast from the flame-retardant magnesium alloy of the present invention has an oxide film of the rare earth element (RE) formed on the outermost surface thereof, and the oxide film of the rare earth element (RE) does not react with iron which becomes a mold at the time of casting, ablation can be suppressed even at a casting site near a gate at a high temperature. That is, the flame-retardant magnesium alloy of the present invention is an alloy having improved ablation resistance, and as a result, the mold temperature during casting can be increased.

Detailed Description

Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the following embodiments.

< flame retardant magnesium alloy >

The magnesium alloy of the present invention is a flame-retardant magnesium alloy containing, in mass%, less than 9.0% of Ca, 0.5% or more and less than 5.7% of Al, 1.3% or less of Si, and 0.4% or more and less than 1.3% of rare earth elements, with the remainder being Mg and unavoidable impurities, and not less than 20.5% of Al +8 Ca.

[ alloy composition ]

The magnesium alloy of the present invention has a metal structure in which (Mg, Al) is formed continuously in a three-dimensional network at grain boundaries around a Mg parent phase (crystal grains)₂A Ca phase, and a Ca-Mg-Si compound phase is formed in the crystal grains (Mg parent phase). These intermetallic phases contribute to the high temperature strength of the magnesium alloy.

(calcium: Ca)

Ca is formed from (Mg, Al)₂The Ca phase and the elements necessary for the Ca-Mg-Si compound phase are present in a range satisfying Al +8Ca ≧ 20.5% as described below. If the Ca content is too large, the proportion of solid solution in the Mg matrix phase increases, which may lower the Mg purity of the Mg matrix phase and lower the thermal conductivity. Therefore, Ca is less than 9.0 mass%, preferably 5.0 mass% or less. The Ca content is preferably 2.5% by mass or more.

(aluminum: Al)

Al is formed from (Mg, Al)₂Elements necessary for the Ca phase are present in a range satisfying Al +8Ca ≧ 20.5% as described below. If the Al content is too large, the ratio of solid solution in the Mg matrix phase increases, which may lower the Mg purity of the Mg matrix phase and lower the thermal conductivity. Therefore, Al is less than 5.7 mass%, preferably 5.0 mass% or less, and more preferably 3.0 mass% or less when heat conduction is emphasized most. The Al content is 0.5 mass% or more, preferably 1.0 mass% or more.

(composition ratio of calcium to aluminum to Al)

In the magnesium alloy of the present invention, Ca and Al need to satisfy the relationship of the following formula (1).

Al+8Ca≧20.5％(1)

When Ca and Al satisfy the relationship of the above formula (1), (Mg, Al) mentioned above is formed₂The Ca phase, as a result, can improve the high-temperature strength. Al +8Ca is preferably 24.0% or more. On the other hand, if the contents of Al and Ca are too highSince the Mg purity of the Mg parent phase may be lowered and the thermal conductivity may be lowered in a large amount, Al +8Ca is preferably 45.0% or less. The reason why 45.0% or less is preferable is that Al is 5 or less and Ca is 5 or less.

In the magnesium alloy of the present invention, the ratio of Al to Ca, i.e., Al/Ca, is preferably 1.7 or less. As mentioned above, Al forms (Mg, Al) together with Ca₂A Ca phase. However, if Al is contained excessively, the ratio of excess Al dissolved in the Mg matrix phase increases, and the Mg purity of the Mg matrix phase may decrease. When the Al/Ca ratio is 1.7 or less, the solid solution of Al in the Mg matrix phase is suppressed, and the thermal conductivity can be improved. Further, Al/Ca is preferably 1.2 or less. In addition, in order to form the above (Mg, Al)₂The Ca phase, Al/Ca, is preferably 0.2 or more.

(silicon: Si)

Si is an element necessary for forming the Ca-Mg-Si compound phase. However, when the Si content is large, coarse SiCa-based compounds combined with Ca are generated, which may inhibit (Mg, Al)₂The formation of the Ca phase as a continuous three-dimensional network is a factor of reducing the high-temperature strength of the magnesium alloy. Therefore, the content of Si is 1.3 mass% or less, preferably 1.0 mass% or less. In addition, the content of Si is preferably 0.2% or more for forming the Ca-Mg-Si based compound phase.

(rare earth element: RE)

The flame-retardant magnesium alloy of the present invention contains a rare earth element (RE). In the flame-retardant magnesium alloy of the present invention, the presence of a specific amount of the rare earth element (RE) forms an oxide film of the rare earth element (RE) on the outermost surface of the molten metal. Therefore, not only the molten metal in the still state but also the molten metal can be stirred, and the combustion of the molten metal can be suppressed.

Further, when a casting is made of the flame-retardant magnesium alloy of the present invention, an oxide film of a rare earth element (RE) is formed on the surface of the casting. Since the oxide film of the rare earth element (RE) does not react with iron which becomes a mold at the time of casting, ablation can be suppressed even at a casting site near a gate at a high temperature. That is, the flame-retardant magnesium alloy of the present invention is an alloy having improved ablation resistance by the presence of a specific amount of rare earth element (RE), and thus the mold temperature during casting can be increased.

The content of the rare earth elements is 0.4 mass% or more, preferably 0.6 mass% or more. The content of the rare earth elements is less than 1.3%, more preferably less than the amount that does not form an unnecessary compound, and for example, preferably less than 1.0%.

Examples of the rare earth element (RE) include scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium, and one kind or two or more kinds of them may be used. In the present invention, cerium (Ce) or lanthanum (La) is preferable among them from the viewpoint that it is effective for improving the corrosion resistance of the magnesium alloy and that it is easily available as a misch metal.

In the flame-retardant magnesium alloy of the present invention, the rare earth element is preferably contained as a misch metal (Mm). The mischmetal (Mm) is a mixture of rare earth metals. Specifically, the misch metal is a mixture which is purified after Nd purification and contains about 40 to 50% of cerium (Ce) and about 20 to 40% of lanthanum (La). Since the separation of rare earth elements into individual elements is expensive, the cost of the obtained flame-retardant magnesium alloy can be reduced by using relatively inexpensive misch metal.

(manganese: Mn)

The flame-retardant magnesium alloy of the present invention preferably contains Mn. Mn has an effect of improving the corrosion resistance of the magnesium alloy. The Mn content is preferably 0.1% or more and 0.5% or less, and more preferably 0.2% or more and 0.4% or less.

The remainder of the flame-retardant magnesium alloy of the present invention is Mg and inevitable impurities. The inevitable impurities are not particularly limited, and are included within a range not affecting the characteristics of the present magnesium alloy.

(Mg purity of Mg parent phase)

The Mg purity of the Mg matrix phase means a content ratio of Mg in crystal grains in the metal structure of the magnesium alloy. In the magnesium alloy of the present invention, the higher the Mg purity of the Mg parent phase, the higher the thermal conductivity of the Mg parent phase, and the higher the thermal conductivity of the magnesium alloy. On the other hand, if components other than Mg are dissolved in the Mg matrix phase to lower the Mg purity, the thermal conductivity of the magnesium alloy is also likely to be lowered.

The flame-retardant magnesium alloy of the present invention preferably has an Mg purity of 98.0% or more in the Mg matrix phase. When the Mg purity of the Mg parent phase is 98.0% or more, a thermal conductivity of 80.0W/mK or more can be obtained. More preferably, the Mg purity of the Mg parent phase is 99.0% or more.

(continuous in the form of a three-dimensional network (Mg, Al)₂Ca photo)

The magnesium alloy of the present invention has a three-dimensional network continuous (Mg, Al)₂A Ca phase. In the form of a three-dimensional net (Mg, Al)₂The Ca phase is represented by a network structure of Mg, Ca, and Al at the grain boundaries around the Mg matrix phase (crystal grains) when the magnesium alloy is cast. By having a solid network of continuous (Mg, Al) at the grain boundaries₂The Ca phase, the magnesium alloy of the present invention, is an alloy having an improved tensile strength at high temperatures.

(Ca-Mg-Si compound phase)

The magnesium alloy of the present invention has a Ca-Mg-Si compound phase in the Mg matrix phase. The Ca — Mg — Si compound phase tends to increase the strength in the crystal grains and the high-temperature strength of the magnesium alloy.

(thermal conductivity)

AZ91D, which is a conventional commercial magnesium alloy, has a thermal conductivity of 51 to 52W/m.K. On the other hand, the thermal conductivity of the aluminum alloy (ADC12 material) was 92W/m · K, and the thermal conductivity of AZ91D was only about half that of the aluminum alloy (ADC12 material). Therefore, the conventional commercial magnesium alloy cannot ensure sufficient heat dissipation as a raw material for high-temperature parts.

In contrast, the magnesium alloy of the present invention has a thermal conductivity of 80.0W/mK or more. Therefore, the magnesium alloy of the present invention has excellent heat dissipation properties as a material for high-temperature parts, and is suitably used as a flame-retardant magnesium alloy for engine members, for example. In addition, as a material of the high-temperature component, in order to secure sufficient heat dissipation, the thermal conductivity is more preferably 90.0W/mK or more, and still more preferably 100.0W/mK or more.

(high temperature Strength)

In the ordinary magnesium alloy, mechanical properties such as tensile strength and elongation are reduced in a high temperature region of about 200 ℃, and high temperature strength equivalent to that of heat-resistant aluminum alloy (ADC12 material) cannot be obtained. In contrast, the magnesium alloy of the present invention has a high-temperature strength of 170MPa or more in tensile strength at 200 ℃. Therefore, the magnesium alloy of the present invention can be suitably used as a flame-retardant magnesium alloy for engine members used in a high-temperature environment, for example. The tensile strength at 200 ℃ is preferably 185MPa or more, more preferably 200MPa or more.

< method for producing flame-retardant magnesium alloy >

The method for producing the magnesium alloy of the present invention is not particularly limited, and for example, a method for melting a metal material containing, in mass%, less than 9.0% of Ca, 0.5% or more and less than 5.7% of Al, 1.3% or less of Si, and 0.4% or more and less than 1.3% of rare earth elements, with the remainder being composed of Mg and unavoidable impurities, and Al +8Ca ≧ 20.5% may be mentioned. The method of high-temperature melting is not particularly limited, and examples thereof include the following methods: a metal material is inserted into a graphite crucible, and is melted by high-frequency induction in an Ar atmosphere and at a temperature of 750 to 850 ℃.

The obtained molten alloy may be injected into a mold for casting. In the casting, the molten metal material may be cooled at a predetermined speed.

The method for producing a magnesium alloy of the present invention preferably includes: a crystallization step of cooling the molten metal material to form a three-dimensional network of continuous (Mg, Al)₂The Ca phase and the Mg parent phase including the Ca-Mg-Si compound phase are crystallized. This makes it possible to obtain a magnesium alloy having improved ablation resistance, while maintaining mechanical properties and thermal conductivity, by suppressing burning of the molten metal not only in the molten metal in a still state but also in the case where the molten metal is stirred.

In addition, the cooling rate is preferably less than 10³K/sec. If it is less than 10³K/sec, the time for discharging the solid solution element in the matrix phase to the crystal phase becomes sufficient during solidification of the Mg matrix phaseAs a result, solid solution elements are less likely to remain in the Mg matrix phase, and the thermal conductivity of the obtained magnesium alloy is less likely to decrease. The cooling rate is preferably 10²K/sec or less.

The method for producing a magnesium alloy of the present invention may further include: a heat treatment step of performing heat treatment at 150-500 ℃. The heat treatment temperature is preferably in the range of 200 to 400 ℃.

The time of the heat treatment step is not particularly limited, and is preferably in the range of 1 to 6 hours.

The magnesium alloy after the heat treatment step may have a higher thermal conductivity than the magnesium alloy without the heat treatment step.

< use >)

The magnesium alloy of the present invention has high-temperature strength, and can suppress temperature rise or thermal expansion to make the clearance of a molded article appropriate. Further, the specific gravity is lower than that of a conventional aluminum alloy, and specifically, weight reduction of 30% or more can be achieved. Therefore, the resin composition can be preferably used for applications requiring high-temperature strength and light weight, and can be suitably used for engine parts such as engine blocks, pistons, and cylinders of automobiles and the like. Moreover, the magnesium alloy of the present invention can contribute to improvement of fuel efficiency of a transportation machine such as an automobile and quietness of an engine.

Examples

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. In addition, "ppm" in examples and comparative examples means "mass ppm" unless otherwise specified.

< example 1 >

[ preparation of molten Metal ]

A metal material in which 4.5 mass% of Al, 4.0 mass% of Ca, 0.3 mass% of Si, 0.3 mass% of Mn, and 0.6 mass% of a misch metal (Mm) are added to Mg is inserted into a crucible, and high-frequency induction melting is performed in an Ar atmosphere to melt at a temperature of 750 to 850 ℃, thereby obtaining a molten alloy (molten metal).

[ production of castings ]

Next, the obtained molten alloy (molten metal) is poured into a mold and cast, and an engine block is manufactured by Die Casting (DC).

Subsequently, the obtained engine block was subjected to heat treatment at 300 ℃ for 4 hours to obtain a heat-treated engine block.

The obtained engine block and heat-treated engine block were measured for thermal conductivity (room temperature) and tensile strength (200 ℃ C.). The results are shown in Table 1.

[ Table 1]

Example 1	Thermal conductivity (at room temperature)	Tensile Strength (at 200 ℃ C.)
			Engine cylinder block	82.2W/m·K	188MPa
Heat treatment engine cylinder body	98.6W/m·K	174MPa

< comparative example 1 >

A molten alloy (molten metal) was obtained in the same manner as in example 1 except that the misch metal (Mm) was not added, and an engine block was produced from the obtained molten alloy (molten metal).

< comparative example 2 >

A molten alloy (molten metal) was obtained in the same manner as in example 1 except that 0.3% of Y was added instead of the misch metal (Mm), and an engine block was produced from the obtained molten alloy (molten metal).

< evaluation >

The following evaluations were made for examples and comparative examples.

[ presence or absence of Combustion of molten Metal ]

The molten alloys (molten metals) obtained in examples and comparative examples were observed for the presence or absence of molten metal combustion during melting (in a stationary state), during Die Casting (DC) (in a stirred state), and in a stationary state after Die Casting (DC). The oxide film formed on the surface of the molten metal after die casting was lifted and observed with the naked eye. The results are shown in Table 2.

[ ablation resistance ]

With respect to the obtained engine block, the presence or absence of ablation was visually confirmed. The results are shown in Table 1. With the engine block obtained in example 1, no ablation was observed even in the region near the gate where the temperature at the time of casting became high. On the other hand, in the engine blocks obtained in comparative example 1 and comparative example 2, ablation was observed in the vicinity of the gate.

It is understood that the engine block obtained in example 1 has an oxide film of a rare earth element (RE) formed on the surface thereof, and the oxide film of the rare earth element (RE) does not react with the material of the mold, that is, iron, and ablation can be suppressed even in the vicinity of the gate having a high temperature. On the other hand, the surfaces of the engine blocks obtained in comparative examples 1 and 2 were calcium oxide films, and therefore, they reacted with a mold, that is, iron, and ablation occurred.

TABLE 2