A high-temperature, high-strength and tough cast magnesium alloy and its preparation method

Abstract

The present invention discloses a high-temperature, high-strength and tough cast magnesium alloy and a preparation method thereof. In terms of mass percentage, the calcium-magnesium alloy component contains 5% - 6% of rare earth elements with high solid solubility, 2% - 3% of rare earth element Y, 1.5% - 3% of zinc, and the balance is magnesium. The preparation method of the magnesium alloy includes the following processes: melting and casting the raw materials of the high-temperature, high-strength and tough cast magnesium alloy to obtain an ingot; after peeling the ingot, performing solution treatment and air-cooling to room temperature to complete the preparation. The cast magnesium alloy finally prepared by the present invention has excellent properties, with a room-temperature yield strength of 205 - 212 MPa, a tensile strength of 257 - 273 MPa, and an elongation rate of 14% - 17%. At the same time, at a high temperature of 300 °C, the tensile strength reaches above 200 MPa, and the elongation rate reaches above 30%, having both high strength and high ductility, providing good processing conditions for subsequent processing.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnesium alloy production, and particularly relates to a high-temperature, high-strength and tough cast magnesium alloy and a preparation method thereof. Background Art

[0002] Magnesium alloy is the lightest structural material in the engineering field and has great application potential in the fields of national defense, military industry, transportation, 3C products, etc. However, due to the relatively low absolute strength of magnesium alloy, poor plastic deformation ability and high-temperature mechanical properties, the wide application of magnesium alloy in structural materials is severely restricted. At present, commercial magnesium alloys mainly include cast magnesium alloys and wrought magnesium alloys. Cast magnesium alloys account for 70% of the total consumption of magnesium alloy products. Therefore, it is necessary to develop high-strength cast high-temperature magnesium alloys to expand the practical application of magnesium alloys.

[0003] At present, adding rare earth elements has become an important way to improve the strength of magnesium alloys. It can not only improve the casting performance of magnesium alloys and refine the grain size, but also some rare earth elements can produce solid solution strengthening and precipitation strengthening effects, comprehensively improving the mechanical properties of alloys. A variety of new magnesium alloys with RE as the main alloying element have been developed successively, such as WE54 and WE43 alloys in the Mg-Y system. After solution aging treatment, the tensile strength is 280-320 MPa, the yield strength is 140-155 MPa, but the elongation is only 5%-12%. The imbalance between strength and plasticity limits its wider application. At 300 °C, the precipitated phases in the alloy soften, grow or even dissolve, unable to play a strengthening role, resulting in a significant decrease in strength, less than 200 MPa, causing premature failure of high-temperature components and unable to meet the requirements of existing technologies. Summary of the Invention

[0004] To solve the problems existing in the existing cast magnesium alloys, the present invention provides a high-temperature, high-strength and tough cast magnesium alloy and a preparation method thereof. The high-temperature, high-strength and tough cast magnesium alloy of the present invention has high strength and good elongation at a relatively high temperature, and can meet the requirements of existing technologies.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A high-temperature, high-strength and tough cast magnesium alloy, in terms of mass percentage, its components contain 5%-6% of rare earth elements with high solid solubility, 2%-3% of rare earth element Y, 1.5%-3% of zinc, and the balance is magnesium.

[0007] Preferably, the rare earth element with high solid solubility is one or both of holmium and erbium.

[0008] Preferably, the mass ratio of the sum of the mass of the rare earth element with high solid solubility and the rare earth element Y to the mass of zinc is 2-6.

[0009] Preferably, the high-temperature, high-strength and tough cast magnesium alloy has a layered structure inside the grains and blocky LPSO phases at the grain boundaries.

[0010] Preferably, the room-temperature yield strength of the high-temperature, high-strength and tough cast magnesium alloy is 205 - 212 MPa, the tensile strength is 257 - 273 MPa, and the elongation is 14% - 17%.

[0011] Preferably, the yield strength of the high-temperature, high-strength and tough cast magnesium alloy at 300 °C is 136 - 142 MPa, the tensile strength is 200 - 203 MPa, and the elongation is 32% - 38%.

[0012] The preparation method of a high-temperature, high-strength and tough cast magnesium alloy as described above in the present invention includes the following processes:

[0013] Melting and casting the raw materials of the high-temperature, high-strength and tough cast magnesium alloy to obtain an ingot;

[0014] After removing the skin of the ingot, performing solution treatment and air-cooling to room temperature to complete the preparation.

[0015] Preferably, the temperature for melting the raw materials is 750 - 780 °C, and the holding time is 25 - 30 min to completely melt the raw materials to obtain alloy liquid;

[0016] Cool the alloy liquid to 710 - 730 °C and let it stand for 5 - 10 min to remove slag, and then perform casting to obtain an ingot.

[0017] Preferably, the temperature of the solution treatment is 500 - 540 °C and the time is 11.5 - 12.5 h.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention uses heavy rare earth elements with a large solid solubility (i.e., rare earth elements with a high solid solubility) as alloying elements, and the content and the content of zinc elements are within a fixed ratio range, which can form long-period stacking ordered structure LPSO phases. The LPSO phase is a high-melting-point phase and has good high-temperature stability in the magnesium matrix, which can avoid the dissolution of precipitation phases at high temperatures and deterioration of the alloy properties, and significantly improve the strength and plasticity of the magnesium alloy. At the same time, the solid solubility of heavy rare earth elements (such as Er, Ho) in the magnesium alloy is relatively large, and various different strengthening phases can be formed at different Zn / RE content ratios, and these strengthening phases can improve the room-temperature strength and high-temperature performance of the alloy. The finally prepared cast magnesium alloy of the present invention has excellent properties, with a room-temperature yield strength of 205 - 212 MPa, a tensile strength of 257 - 273 MPa, and an elongation of 14 - 17%. At the same time, at a high temperature of 300 °C, the tensile strength reaches more than 200 MPa and the elongation reaches more than 30%, combining high strength and high ductility, providing good processing conditions for subsequent processing.

[0020] In the preparation method of the present invention, the present invention regulates the alloy microstructure through simple heat treatment. After solidification, the alloy grains are relatively large, and the precipitated phases also mostly present a coarse network structure, which is not conducive to the mechanical properties of the alloy. Therefore, solution treatment is adopted to adjust the shape and size of the alloy precipitated phases, exert its precipitation strengthening effect, and comprehensively improve the mechanical properties of the alloy. Description of the Drawings

[0021] Figure 1 It is a comparison chart of the room temperature mechanical properties of the high-temperature high-strength and tough cast magnesium alloy obtained in each embodiment of the present invention and the existing cast magnesium alloy;

[0022] Figure 2 It is a comparison chart of the mechanical properties of the high-temperature high-strength and tough cast magnesium alloy obtained in each embodiment of the present invention and the existing cast magnesium alloy at 200 °C;

[0023] Figure 3 It is a microstructural characteristic diagram of the high-temperature high-strength and tough cast magnesium alloy obtained in Example 1 of the present invention;

[0024] Figure 4 It is a microstructural characteristic diagram of the high-temperature high-strength and tough cast magnesium alloy obtained in Example 2 of the present invention;

[0025] Figure 5 It is a microstructural characteristic diagram of the high-temperature high-strength and tough cast magnesium alloy obtained in Example 3 of the present invention. Detailed Embodiments

[0026] The present invention will be further described below with reference to the drawings and embodiments.

[0027] The technical solution of the present invention introduces one or two of the heavy rare earth elements holmium and erbium with high solid solubility in the magnesium matrix, so that the mass ratio of the rare earth element to the zinc element is 2-6.

[0028] The preparation method of the high-temperature high-strength and tough cast magnesium alloy of the present invention includes the following steps:

[0029] 1. Select raw materials: Weigh 5%-6% of the high solid solubility rare earth element, 2%-3% of the rare earth element Y, and 1.5%-3% of zinc by mass, and the rest is magnesium. Among them, the high solid solubility rare earth element is one or two of holmium and erbium.

[0030] 2. Place the raw materials in an electric resistance furnace, heat up to 750-780 °C, and keep warm for 25-30 min to make the alloy fully dissolve and diffuse into the melt to obtain a uniform alloy liquid. Then cool down to 710-730 °C, let the alloy liquid stand for 5-10 min to remove the surface scum. Finally, carry out casting to obtain a magnesium alloy billet.

[0031] 3. Turn the skin of the magnesium alloy billet, and then perform solution treatment on the magnesium alloy billet to make the alloy composition uniform. The solution treatment temperature is 500 - 540 °C. After holding for 11.5 - 12.5 h in the furnace, take it out and air-cool it to room temperature to obtain the high-temperature, high-strength and tough cast magnesium alloy. The present invention can adjust the solubility of rare-earth solute atoms in the magnesium matrix by changing the solution treatment temperature.

[0032] The present invention only uses the solution process to improve the alloy properties. It can adjust the solubility of rare-earth solute atoms in the magnesium matrix by changing the temperature of the solution treatment described above, so as to obtain second phases with different microstructures, thereby improving the plasticity and toughness of the alloy. At the same time, it also plays a certain solution strengthening role, saves energy, has a simple process, and has the potential for popularization and application.

[0033] Example 1

[0034] The preparation method of the high-temperature, high-strength and tough cast magnesium alloy in this example includes the following steps:

[0035] 1. Select raw materials: Weigh 5% of high-solubility rare-earth elements, 2% of rare-earth element Y, and 1.5% of zinc by mass percentage, and the rest is magnesium. Among them, the high-solubility rare-earth element is holmium.

[0036] 2. Put the raw materials in an electric resistance furnace, heat up to 750 °C, and hold for 25 min to make the alloy fully dissolve and diffuse into the melt to obtain a uniform alloy liquid. Then cool down to 710 °C, let the alloy liquid stand for 5 min, and remove the surface scum. Finally, perform casting to obtain a magnesium alloy billet.

[0037] 3. Turn the skin of the magnesium alloy billet, and then perform solution treatment on the magnesium alloy billet to make the alloy composition uniform. The solution treatment temperature is 500 °C. After holding for 11.5 h in the furnace, take it out and air-cool it to room temperature to obtain the high-temperature, high-strength and tough cast magnesium alloy.

[0038] Example 2

[0039] The preparation method of the high-temperature, high-strength and tough cast magnesium alloy in this example includes the following steps:

[0040] 1. Select raw materials: Weigh 6% of high-solubility rare-earth elements, 3% of rare-earth element Y, and 3% of zinc by mass percentage, and the rest is magnesium. Among them, the high-solubility rare-earth element is erbium.

[0041] 2. Put the raw materials in an electric resistance furnace, heat up to 780 °C, and hold for 30 min to make the alloy fully dissolve and diffuse into the melt to obtain a uniform alloy liquid. Then cool down to 720 °C, let the alloy liquid stand for 10 min, and remove the surface scum. Finally, perform casting to obtain a magnesium alloy billet.

[0042] 3. Turn the magnesium alloy ingot, and then perform solution treatment on the magnesium alloy ingot to make the alloy composition uniform. The solution treatment temperature is 520 °C. After holding for 12 h in the furnace, take it out and air-cool it to room temperature to obtain a high-temperature, high-strength and high-toughness cast magnesium alloy.

[0043] Example 3

[0044] The preparation method of the high-temperature, high-strength and high-toughness cast magnesium alloy in this example includes the following steps:

[0045] 1. Select raw materials: Weigh 5.5% of high-solid-solubility rare earth elements, 2.5% of rare earth element Y, and 2% of zinc by mass percentage, and the rest is magnesium. Among them, the high-solid-solubility rare earth elements are a mixture of holmium and erbium, the content of holmium is 2%, and the content of erbium is 2.5%.

[0046] 2. Place the raw materials in an electric resistance furnace, heat up to 760 °C, and hold for 30 min to allow the alloy to fully dissolve and diffuse into the melt to obtain a uniform alloy liquid. Then cool down to 730 °C, let the alloy liquid stand for 10 min to remove the surface scum. Finally, perform casting to obtain a magnesium alloy ingot.

[0047] 3. Turn the magnesium alloy ingot, and then perform solution treatment on the magnesium alloy ingot to make the alloy composition uniform. The solution treatment temperature is 540 °C. After holding for 12.5 h in the furnace, take it out and air-cool it to room temperature to obtain a high-temperature, high-strength and high-toughness cast magnesium alloy.

[0048] See Figure 1 , the room-temperature mechanical property parameters of the high-temperature, high-strength and high-toughness cast magnesium alloy obtained in Examples 1 to 3 are shown in Table 1:

[0049] Table 1

[0050] Example Yield strength (MPa) Tensile strength (MPa) Elongation rate (%) Example 1 205 257 14％ Example 2 212 273 17％ Example 3 209 265 16％ WE54 alloy 205 250 9％ WE43 alloy 180 250 6％ AE44 alloy 140 247 11％

[0051] As can be seen from Table 1, the room-temperature yield strength of the high-temperature, high-strength and high-toughness cast magnesium alloy of the present invention is 205 - 212 MPa, the tensile strength is 257 - 273 MPa, and the elongation is 14% - 17%, all of which are higher than the existing WE54 alloy, WE43 alloy and WE44 alloy.

[0052] See Figure 2 , the mechanical property parameters of the high-temperature, high-strength and high-toughness cast magnesium alloy obtained in Examples 1 to 3 at 300 °C are shown in Table 2:

[0053] Table 2

[0054] Example Yield strength (MPa) Tensile strength (MPa) Elongation rate (%) Example 1 136 200 32％ Example 2 142 203 38％ Example 3 139 201 35％ WE54 alloy 120 145 10％ WE43 alloy 120 170 15％ AE44 alloy 90 102 13％

[0055] As can be seen from Table 1, the high-temperature high-strength and tough cast magnesium alloy of the present invention has a yield strength of 136-142 MPa, a tensile strength of 200-203 MPa, and an elongation of 32%-38% at 300 °C, all of which are higher than the existing WE54 alloy, WE43 alloy, and WE44 alloy.

[0056] In summary, compared with the existing cast magnesium alloys, the alloy of the present invention has improved yield strength, tensile strength, and elongation at room temperature and high temperature, and the strength and toughness are more balanced.

[0057] See Figure 3 , Figure 4 , Figure 5 , after solution treatment, the distribution state of the long-period structure shows regular changes. As the solution temperature increases, the LPSO phase at the grain boundary gradually decreases, and the intragranular lamellar structure gradually increases. When the LPSO phase and the intragranular stacking fault structure at the grain boundary and in the grains reach a certain proportion, they can jointly play a role in hindering the dislocation of the intragranular and grain boundary precipitation phases, improving the alloy strength. In addition, the stacking fault energy of the LPSO phase and the stacking fault structure is relatively low, which can promote the activation of more slip systems, thereby improving the plasticity of the alloy. Therefore, the alloy obtains high strength and plasticity. For the single grain boundary LPSO phase and intragranular stacking fault structure, due to the lack of their effects on the intragranular dislocation and grain boundary slip deformation mechanisms respectively, their strength and plasticity are relatively low. Compared with the nano-precipitation phases of other system alloys, due to the low thermal stability of their precipitation phases and the decomposition or growth at high temperature, the hindering effect on dislocation slip / climb at high temperature is weakened. Although they have comparable room temperature strength with this alloy, their plasticity is relatively low, and their high temperature strength is much lower than that of this alloy. Moreover, due to the existence of the LPSO phase and the stacking fault structure in this alloy, its excellent plasticity coordination ability enables this alloy to show good plasticity at 300 °C high temperature.

[0058] The microstructure of the high-temperature high-strength and tough cast magnesium alloy of the present invention is that a large number of lamellar structures are precipitated inside the grains, and a small amount of massive LPSO phase exists at the grain boundaries.

Claims

1. A high-temperature, high-strength and high-toughness cast magnesium alloy, characterized in that, By mass percentage, its components contain 5% - 6% of rare earth elements with high solid solubility, 2% - 3% of rare earth element Y, 1.5% - 3% of zinc, and the balance is magnesium; The rare earth elements with high solid solubility are one or both of holmium and erbium; The mass ratio of the sum of the mass of rare earth elements with high solid solubility and rare earth element Y to the mass of zinc is 2 - 6; The high-temperature high-strength and tough cast magnesium alloy is prepared through the following process: Melting and casting the raw materials of the high-temperature high-strength and tough cast magnesium alloy to obtain an ingot; After removing the skin of the ingot, performing solution treatment, and air-cooling to room temperature, the preparation is completed; Among them, the temperature of the solution treatment is 500 - 540 °C and the time is 11.5 - 12.5 h; The high-temperature high-strength and tough cast magnesium alloy has a layered structure inside the grains and massive LPSO phases at the grain boundaries; The high-temperature high-strength and tough cast magnesium alloy has a yield strength of 136 - 142 MPa, a tensile strength of 200 - 203 MPa, and an elongation of 32% - 38% at 300 °C.

2. The high-temperature high-strength and high-toughness cast magnesium alloy according to claim 1, characterized in that, The high-temperature high-strength and tough cast magnesium alloy has a yield strength of 205 - 212 MPa, a tensile strength of 257 - 273 MPa, and an elongation of 14% - 17% at room temperature.

3. The preparation method of a high-temperature, high-strength and high-toughness cast magnesium alloy according to claim 1, characterized in that, Including the following process: Melting and casting the raw materials of the high-temperature high-strength and tough cast magnesium alloy to obtain an ingot; After removing the skin of the ingot, performing solution treatment, and air-cooling to room temperature, the preparation is completed; Among them, the temperature of the solution treatment is 500 - 540 °C and the time is 11.5 - 12.5 h.

4. The preparation method of a high-temperature, high-strength and tough cast magnesium alloy according to claim 3, characterized in that, The temperature during melting of the raw materials is 750 - 780 °C, and the holding time is 25 - 30 min to completely melt the raw materials to obtain an alloy liquid; Cooling the alloy liquid to 710 - 730 °C and standing for 5 - 10 min to remove slag, and then performing casting to obtain an ingot.

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