阅读说明：本技术 一种含Ce基混合稀土的高强度AZ81镁合金材料及其制备工艺 (High-strength AZ81 magnesium alloy material containing Ce-based misch metal and preparation process thereof ) 是由 祝向荣 李贺超 汤文瑄 王金敏 于 2019-10-30 设计创作，主要内容包括：本发明公开了一种含Ce基混合稀土的高强度AZ81镁合金材料及其制备工艺。高强度AZ81镁合金材料的组分为：Al 7.5~8.0 wt%,Zn 0.5~0.7 wt％,Ce基混合稀土0.01~2.1 wt%,杂质元素<0.2 wt%,余量为Mg。镁合金制备方法涉及熔炼、热挤压以及T6热处理等工艺。混合稀土元素的添加增强了合金的固溶强化效应的同时,细化了合金的晶粒,由此形成了细晶强化效应；而通过热挤压和T6热处理工艺,在合金中析出含稀土元素的第二相,形成第二相强化效应。综合以上强化机制,合金的抗拉强度较未添加稀土元素的AZ81镁合金大为增加,最大提高到368 MPa,满足了合金在航空航天领域的使用要求。(The invention discloses a high-strength AZ81 magnesium alloy material containing Ce-based misch metal and a preparation process thereof, wherein the high-strength AZ81 magnesium alloy material comprises the following components of Al 7.5 ~.0 wt%, Zn 0.5 ~.7 wt%, Ce-based misch metal 0.01 ~.1 wt%, impurity elements less than 0.2 wt%, and the balance Mg. magnesium alloy preparation method relates to processes of smelting, hot extrusion, T6 heat treatment and the like, the addition of the misch metal enhances the solid solution strengthening effect of the alloy and simultaneously refines the crystal grains of the alloy, thereby forming a fine grain strengthening effect, and a second phase containing rare earth elements is precipitated in the alloy through the hot extrusion and T6 heat treatment processes to form a second phase strengthening effect.)

1. The high-strength AZ81 magnesium alloy material containing Ce-based misch metal is characterized by comprising 7.5 ~ 8.0.0 wt% of Al, 0.5 ~ 0.7.7 wt% of Zn, 0.01 ~ 2.1.1 wt% of rare earth element RE, 0.2 wt% of impurity element and the balance of Mg, wherein the total weight of the alloy material meets 100%, the rare earth element RE comprises Ce, Y, Nd and La elements, and the mass content of Ce in the rare earth element RE is more than or equal to 60%.

2. The high-strength AZ81 magnesium alloy material containing Ce-based misch metal according to claim 1, characterized in that it consists of Al 7.5 ~ 8.0.0 wt%, Zn 0.5 ~ 0.7 wt%, rare earth element RE 0.6 ~ 2.05.05 wt%, impurity element <0.2 wt%, and the balance Mg, the total weight of which is 100%.

3. The high-strength AZ81 magnesium alloy material containing Ce-based misch metal according to claim 1, characterized in that it consists of Al 7.5 ~ 8.0.0 wt%, Zn 0.5 ~ 0.7 wt%, rare earth element RE 1.2 ~ 1.8.8 wt%, impurity element <0.2 wt%, and the balance Mg, the total weight of which is 100%.

4. The preparation process of the high-strength AZ81 magnesium alloy containing Ce-based misch metal according to claim 1, characterized by comprising the following steps:

(1) mixing and smelting AZ91 alloy, pure magnesium and Ce-containing mischmetal with Ce content not less than 60% to obtain as-cast alloy;

(2) and (3) peeling the as-cast alloy, and performing hot extrusion at 400 ~ 450 ℃ to obtain a plate with the extrusion ratio of 15 ~ 20.

5. The preparation process of claim 4, wherein the step (2) is followed by a step (3) of cutting a sheet material with a proper length from the extruded sheet, carrying out T6 heat treatment, namely carrying out solid solution at 390 ~ 430 ℃ for 1 ~ 3 hours and at 170 ~ 190 ℃ for 22 ~ 26 hours to obtain the high-strength AZ81 magnesium alloy containing Ce-based misch metal.

Technical Field

The invention relates to the technical field of metal materials, in particular to a high-strength AZ81 magnesium alloy material containing Ce-based misch metal and a preparation process thereof.

Background

The magnesium alloy is used as the lightest engineering metal material, has small density, high specific strength and specific rigidity, good castability and machinability, and increasingly receives attention in the aspects of automobile weight reduction and environmental protection. In addition, magnesium alloys have been used for the production of parts such as instrument panels, seat frames, guard rails, steering wheels, and steering columns for automobiles. Although the application approaches of magnesium alloy are more, China has more magnesium manufacturers, smaller scale, single product and laggard processing mode.

The conventional magnesium alloys are mainly classified into Mg-Al series, Mg-Zr series, Mg-RE series, etc., and among these alloys, AZ81, which is Mg-Al series, is widely used due to its low cost and excellent casting property. But also has the defects of poor cold processing capability, low yield and insufficient mechanical property, and can not meet the requirements of high-strength magnesium alloy products, thereby limiting the application of the magnesium alloy products. With the continuous promotion of the application of magnesium alloy in the fields of 3C and aerospace, China urgently needs to independently research and develop high-strength magnesium alloy applied to electronic product shells and aviation instrument shells, and urgently needs to improve the yield of the magnesium alloy.

Disclosure of Invention

In order to overcome the defect of low strength of AZ81 magnesium alloy in the prior art, the invention aims to provide a high-strength AZ81 magnesium alloy material containing Ce-based misch metal and a preparation process thereof. According to the invention, a small amount of Ce-based mixed rare earth elements are added into the AZ81 magnesium alloy, so that the mechanical properties of the AZ81 magnesium alloy are greatly improved.

The technical scheme of the invention is specifically introduced as follows.

A high-strength AZ81 magnesium alloy material containing Ce-based misch metal comprises the following elements: 7.5-8.0 wt% of Al, 0.5-0.7 wt% of Zn, 0.01-2.1 wt% of rare earth element RE, less than 0.2 wt% of impurity elements and the balance of Mg, wherein the total weight of the alloy is 100%; wherein: the rare earth element RE comprises Ce, Y, Nd and La elements, and the mass content of Ce in the rare earth element RE is more than or equal to 60%.

Preferably, the high-strength AZ81 magnesium alloy material containing Ce-based misch metal consists of the following elements: 7.5-8.0 wt% of Al, 0.5-0.7 wt% of Zn, 0.6-2.05 wt% of rare earth element RE, less than 0.2 wt% of impurity elements and the balance of Mg, wherein the total weight of the alloy is 100%;

more preferably, the high-strength AZ81 magnesium alloy material containing Ce-based misch metal consists of the following elements: 7.5-8.0 wt% of Al, 0.5-0.7 wt% of Zn, 1.2-1.8 wt% of rare earth element RE, less than 0.2 wt% of impurity elements and the balance of Mg, wherein the total weight of the alloy meets 100%.

The invention further provides a preparation process of the high-strength AZ81 magnesium alloy containing Ce-based misch metal, which comprises the following steps:

(1) mixing and smelting AZ91 alloy, pure magnesium and Ce-containing mischmetal with Ce content not less than 60% to obtain as-cast alloy;

(2) and (3) peeling the as-cast alloy, and performing hot extrusion at 400-450 ℃ to obtain a plate, wherein the extrusion ratio is 15-20.

Further, the method also comprises a step (3) after the step (2): cutting a plate with a proper length on a pressing plate, carrying out T6 heat treatment, namely carrying out solid solution at the temperature of 390-430 ℃ for 1-3 hours, and carrying out aging at the temperature of 170-190 ℃ for 22-26 hours to obtain the high-strength AZ81 magnesium alloy containing Ce-based misch metal.

Compared with the prior art, the invention has the advantages that:

1. the content of the mixed rare earth used in the magnesium alloy is 0.01-2.1 wt%, the content is less, and the cost is relatively controllable.

2. Because the mixed rare earth elements are added into the magnesium alloy, the alloy grains are refined, a proper amount of second phase is precipitated, the solid solution strengthening effect is maintained, the effects of fine crystal strengthening and second phase strengthening are achieved, the tensile strength of the alloy can be effectively increased, the tensile strength of the magnesium alloy at room temperature is above 320MPa, and the magnesium alloy is far superior to AZ81 magnesium alloy not doped with the rare earth elements.

3. The tensile strength of the alloy is further improved through a heat treatment process, the tensile strength of the magnesium alloy at room temperature is 368MPa which is far higher than that of the AZ31 magnesium alloy which is commercially used at present, and the requirement of aerospace on the mechanical property of the magnesium alloy can be met.

Drawings

Fig. 1 is a gold phase diagram of AZ81-x wt.% RE ((a), (b): x ═ 0.61 wt.%, (c), (d): x ═ 1.22 wt.%, (e), (f): x ═ 1.73 wt.%, (g), (h): x ═ 2.02 wt.%); (a) (c), (e), (g) in the extruded state; (b) t6 in the heat-treated state.

Fig. 2 shows the change in tensile strength of the AZ81-xY (x is 0,0.5,1.0,1.5,2.0 wt.%) magnesium alloy in the extruded state and in the heat treated state of T6 at room temperature.

Detailed Description

In the invention, the Ce-based mixed rare earth is adopted to dope the magnesium alloy, the main rare earth element in the Ce-based mixed rare earth is Ce, and the rest comprises rare earth elements such as Y, Nd, La and the like.

The inventor researches and discovers that the microstructure of the AZ81 magnesium alloy is obviously changed after the Ce-based misch metal element is added into the AZ81 magnesium alloy. The most remarkable characteristic is that the crystal grains are obviously refined, and in the alloy structure, short rod-shaped precipitated phases are generated and are dispersed and distributed. Ce-based high-melting-point compounds can be separated out, and on one hand, the compounds hinder the growth of grains and further refine the grains; on the other hand, these compounds are strengthening phases, and therefore this results in an increase in the strength of the magnesium alloy. In addition, the addition of Ce also increases the amount of intragranular precipitated phases, which makes the magnesium alloy easier to form.

And with regard to other elements in the mixed rare earth elements, the strengthening of the Y element to the magnesium alloy is mainly realized by solid solution strengthening, dispersion strengthening and fine grain strengthening, so that the strength of the magnesium alloy at room temperature is obviously improved, and the ductility and toughness of the magnesium alloy are also improved. Since the Y element is an alloy element having a high melting point, when added to a magnesium alloy, it increases the nucleation rate of the alloy, and thus it can refine the crystal grains, which is particularly significant in AZ81 magnesium alloy. Meanwhile, dispersed second phase particles are separated out after the Y element is added, so that dispersion strengthening is formed. Therefore, the Y element can improve the strength of the magnesium alloy.

The Nd element mainly plays a role in solid solution strengthening on the magnesium alloy. A small amount of Nd element can obviously refine the crystal grains of the AZ81 magnesium alloy, obviously increase precipitated phases and play a role in dispersion strengthening. Therefore, the Nd element can also increase the strength of the magnesium alloy at room temperature. La YuanThe element can make the second phase of the AZ81 magnesium alloy present granular distribution and discontinuous network distribution, and can also enhance the effect of precipitation strengthening. In addition, La reacts with Al to generate Al with high melting point and dispersed distribution₁₁La₃The phase not only can strengthen the magnesium alloy matrix, but also can pin grain boundaries and dislocation, so that the grain size is reduced, and the strength of the magnesium alloy is improved.

From the above, adding a small amount of rare earth elements such as Ce, Y and the like into the AZ81 magnesium alloy can refine the microstructure of the magnesium alloy and obviously improve the mechanical property. When two or more rare earth elements are added into the magnesium alloy, the precipitation of supersaturated solid solution is influenced among the rare earth elements within a certain element content range, and an additional strengthening effect can be generated, so that the tensile strength of the alloy is improved. Therefore, the Ce-based misch metal is the correct choice as a doping element for high strength AZ81 magnesium alloys. In addition, the alloy is also heat treated to further improve the strength of the alloy. After the alloy is subjected to heat treatment, the second phase can be continuously precipitated and dispersed, and the mechanical property of the magnesium alloy is improved.

The technical scheme of the invention is described in the following by combining the drawings and the specific embodiment.

The invention adopts the following process to prepare the high-strength AZ81 magnesium alloy containing Ce-based misch metal, and comprises the stages of smelting, hot extrusion, T6 heat treatment and the like. The specific process comprises the following steps:

(1) the smelting material is selected from commercial AZ91 magnesium alloy, pure Mg (99.99 percent) and Ce-based mischmetal (the Ce content is more than or equal to 60 percent).

(2) Preparing furnace charge, removing the corrosive on the crucible wall, and preheating all raw materials, flux, moulds and the like to above 300 ℃ in advance. And a protective gas device is connected, high-purity inert gas is used as protective gas, and the whole course protection is required during smelting. The temperature is required to be controlled at any time in the smelting process, so that the thermocouple is placed in the crucible, and the temperature of the alloy liquid is detected in real time.

(3) And (3) placing the AZ91 alloy and pure magnesium in a smelting furnace, heating to 720-740 ℃, adding mixed rare earth, completely melting the materials, and stirring for 3-5 minutes to homogenize the distribution of alloy elements. During the smelting process, a little slag is formed. And after removing the slag, adjusting the temperature of the alloy liquid to 750-760 ℃, and standing for about 15 minutes.

(4) And after standing, cooling the alloy liquid to 700-720 ℃, then conveying the alloy liquid into a heat preservation furnace by a pouring pump, cooling the alloy liquid by a crystallizer communicated with the heat preservation furnace, and performing extrusion and drawing molding by using double rollers to obtain the as-cast alloy. Cutting the as-cast alloy into pieces by a sawing machineAnd (4) ingot shape. The as-cast alloy was descaled using a lathe.

(5) And carrying out hot extrusion on the peeled cast alloy to obtain a plate, wherein the extrusion temperature is 400-450 ℃, and the extrusion ratio is 15-20. And (3) directly preparing a part of the plate into a metallographic sample and a tensile sample respectively, and observing a microstructure and testing mechanical properties.

(6) And carrying out T6 heat treatment (solution treatment and artificial aging) on the other part of the plate, carrying out solution treatment at 390-430 ℃ for 1-3 hours, and aging at 170-190 ℃ for 22-26 hours.

Table 1 shows the four alloy compositions produced using the same process parameters of reaction temperature and reaction time. FIG. 1 shows the metallographic microstructure of the samples of 4-component alloys prepared by the same process parameters of reaction temperature and reaction time after hot extrusion and T6 heat treatment, wherein the alloy numbers are 1#, 2#, 3# and 4 #. As can be seen from Table 1, the content of Al element in the alloy sample is 7.5-8.0 wt.%, the content of Zn element is 0.5-0.7 wt.%, and the content of the mischmetal is gradually increased. It can be seen in fig. 1 that as the misch metal content increases, the grains become finer, the precipitated phases increase, and the second phase of the T6 heat treated alloy precipitates more than the extruded alloy.

TABLE 1 composition of Ce-based misch metal AZ81

The mechanical properties of the alloy are mainly examined for elongation and tensile strength, and the mechanical properties are measured by a room-temperature tensile test. The room temperature tensile test is carried out on a WDW-100C electronic universal tester according to the national standard, and the tensile rate is 1 mm/min. Table 2 shows the mechanical properties of the above prepared samples of the blended rare earth magnesium alloy, as well as commercial AZ31 and non-rare earth AZ81 magnesium alloy, in the extruded and T6 heat treated state, at room temperature. FIG. 2 shows the change in tensile strength of each of the rare earth doped magnesium alloy and the non-rare earth doped AZ81 magnesium alloy samples in the as-extruded and T6 heat treated states.

TABLE 2 mechanical properties of AZ81-xRE alloy in extruded, T6 heat-treated state, commercial AZ31 magnesium alloy

As can be seen from table 2 and fig. 2, the tensile strength of the alloy with the rare earth element added is greatly increased compared with the magnesium alloy without the rare earth element added, and the tensile strength is maximized when the content of the misch metal is 1.73 wt.% (alloy # 3); when the content of the misch metal is 2.02 wt.% (4# alloy), the tensile strength is reduced compared with that of the 3# alloy, because the content of the misch metal is too much, a second phase containing the rare earth is formed too much, the matrix is easy to crack, and the fine crystal strengthening and solid solution strengthening effects of the rare earth elements are reduced. It was also found that the tensile strength of the alloy after heat treatment at T6 was further improved than that of the as-extruded sample. The 3# sample has the highest tensile strength of 368MPa after being subjected to T6 heat treatment, which is greatly higher than AZ81 magnesium alloy without mixed rare earth and also higher than AZ31 magnesium alloy with wider market application, and the requirement of aerospace on the mechanical property of the magnesium alloy can be met. It is noted that as the content of the misch metal in the alloy increases, the elongation tends to decrease.