High-rigidity Mg-Al magnesium alloy material

Abstract

The invention discloses a high-rigidity Mg-Al series magnesium alloy material which comprises main alloy elements Al and Ca, the content of Ca is 15 wt.%-30 wt.%, and the mass ratio of Ca to Al is 0.4-1. Preferably, the content of Ca is 15.5 wt.%-27 wt.%, and the total content of Al and Ca is greater than or equal to 31 wt.%. By regulating and controlling the Ca content and the Ca / Al mass ratio, a high-modulus C36 or C15 phase is formed to the maximum extent, and plasticity is kept while the elasticity modulus is improved. The magnesium alloy material is high in elasticity modulus, high in rigidity and good in heat resistance, and can be applied to service scenes with higher requirements for material light weight, rigidity, dimensional stability and wear resistance.

Description

Technical Field

[0001] The present invention relates to a high-stiffness Mg-Al series magnesium alloy material, belonging to the technical field of light non-ferrous metals. Background Art

[0002] Magnesium alloy is the lightest metal structural material in practical applications and is an important lightweight material in fields such as aerospace, transportation, electronics 3C, unmanned aerial vehicles, and humanoid robots. At present, the strength and elongation of magnesium alloys are close to those of conventional aluminum alloys, but their elastic modulus is only about 45 GPa, far lower than 72 GPa of aluminum alloys. Compared with aluminum alloy parts of the same specification, under the same stress state, magnesium alloy parts will produce greater elastic deformation and poor dimensional stability. Taking spacecraft and unmanned aerial vehicles as examples, for cabin and bracket parts containing precision instruments, during the operation of the spacecraft, conventional magnesium alloy parts will have too large an amplitude due to the low elastic modulus, thus affecting the control accuracy. In addition, humanoid robots need to withstand external forces during service, so they need to have the ability to resist elastic deformation, which is the basis for the precise control of robots. Similarly, magnesium alloys are required to have a higher elastic modulus. At present, only by increasing the cross-sectional area can the stiffness of magnesium alloy parts be improved, but this will weaken the weight reduction effect of magnesium alloys.

[0003] Mg-Al series magnesium alloys are the most widely used magnesium alloys at present, which is due to the low cost and high comprehensive mechanical properties of this series of magnesium alloys. Among them, AZ91D is the current mainstream high-strength magnesium alloy, which is widely used in various low-temperature and high-load-bearing service environments. AM50 and AM60 are the current mainstream die-cast magnesium alloys, which are widely used in the manufacture of various automotive die-castings such as seat frames and instrument panel brackets.

[0004] The design of conventional high-stiffness magnesium-based materials mainly relies on the method of externally adding high-modulus reinforcing phases (such as SiC, Al2O3) to improve stiffness. However, while the modulus is improved, the plasticity of the material will be severely deteriorated. The root cause of this stiffness-plasticity mismatch problem is largely due to the lack of a strong interfacial bond between the externally added reinforcing phase and the matrix. Adding Ca to the Mg-Al system will in-situ react to form C36-(Mg,Al)2Ca or C15-Al2Ca phases, but the existing technology only focuses on the effect of Ca on improving heat resistance and flame retardancy, and does not fully explore the role of C36 or C15 phases in improving stiffness. Summary of the Invention

[0005] In view of the above prior art, the purpose of the present invention is to provide a high-stiffness Mg-Al series magnesium alloy material, which has a high elastic modulus, high stiffness, and good heat resistance, and can be applied to service scenarios with higher requirements for material lightweight, stiffness, dimensional stability, and wear resistance.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A high-rigidity Mg-Al magnesium alloy material comprises main alloying elements Al and Ca, wherein the Ca content is 15 wt.% to 30 wt.%, and the Ca / Al mass ratio is 0.4 to 1.

[0007] Preferably, the Ca content is 15.5 wt.% to 27 wt.%, and the total content of Al and Ca is ≥31 wt.%.

[0008] More preferably, the Ca / Al mass ratio is 0.75.

[0009] Preferably, the magnesium alloy material of the present invention may further contain auxiliary alloying elements and / or high modulus reinforcing phases.

[0010] Preferably, the total content of the auxiliary alloy elements is ≤20wt.%; the high modulus reinforcing phase is one or more of SiC, Al2O3, ZrO2, TiC, carbon nanotubes, graphene, carbon fiber, ZrB2, TiB2, B4C, AlN, titanium and titanium alloys, and high entropy alloys.

[0011] The auxiliary alloying elements may be one or more of Ag, Au, B, Ba, Be, Bi, Cd, Ce, Co, Cr, Cu, Fe, Ga, Ge, Hg, I, In, K, Li, Mn, Mo, Na, Nb, Ni, Os, P, Pb, Pd, Pt, RE (lanthanide and actinide rare earth elements), Rh, Ru, Sb, Sc, Se, Si, Sm, Sn, Sr, Ta, Te, Tn, Tl, Ti, U, V, W, Y, Zn, and Zr.

[0012] The high modulus reinforcement phase may be in the form of particles, fibers, sheets or whiskers.

[0013] Beneficial effects of the present invention: The present invention forms a high modulus C36 or C15 phase to the maximum extent by regulating the Ca content and the Ca / Al mass ratio. The C36 and C15 phases have a certain plastic deformation ability, which is better than other second phases formed in the Mg-Al-Ca system, such as the A12 phase and the C14 phase. Therefore, the magnesium alloy material of the present invention can achieve an increase in the elastic modulus while maintaining plasticity.

[0014] The magnesium alloy material provided by the present invention has a high elastic modulus (≥55 GPa), high rigidity, and good heat resistance, and can be applied to service scenarios that have higher requirements on material lightweight, rigidity, dimensional stability, and wear resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1The figure is a comparison of the room temperature elastic modulus of each cast magnesium alloy in Example 1 and Example 2.

[0016] Figure 2 1 and 2 are metallographic microstructure diagrams of the cast magnesium alloys in Example 1 and Example 2.

[0017] Figure 3 This is the microstructure of AG2418+3wt.%Si in Example 3.

[0018] Figure 4 Polarization curves and corrosion current density of AG2418 and AG2418+3wt.%Si in 3.5%NaCl solution in Example 3.

[0019] Figure 5 This is a comparison diagram of the microstructures of AG3224 and 0.1wt.% SiC / AG3224 in Example 4. DETAILED DESCRIPTION

[0020] The present invention provides a high-rigidity Mg-Al magnesium alloy material with an elastic modulus of ≥55 GPa, which improves the elastic modulus while maintaining plasticity.

[0021] The low-cost element Ca added to the Mg-Al magnesium alloy of the present invention can form C36 or C15 phases through in-situ reaction. These two phases not only have high heat resistance, but also have high elastic modulus, and the elastic modulus can reach ~100 GPa. The interface bonding strength between the reinforcing phase and the matrix generated by in-situ reaction in the magnesium alloy melt, and the C36 or C15 phase itself has a certain plastic deformation ability, thereby improving the plasticity of the material. In the present invention, the purpose of regulating the Ca / Al mass ratio is to maximize the formation of high modulus C36 or C15 phases and avoid the formation of low modulus C14-Mg2Ca (~49GPa) and A12-Mg17Al12 phases (~50GPa). Preferably, the Ca content is 15.5 wt.%~27 wt.%, and the total content of Al and Ca is ≥31wt.%, in order to increase the volume fraction of C36 or C15 phases so that the room temperature elastic modulus is ≥55GPa.

[0022] Therefore, the present invention adjusts the Ca content and the Ca / Al mass ratio to maximize the formation of high modulus C36 or C15 phase, thereby improving the elastic modulus while maintaining the plasticity, thereby obtaining a lightweight, high-rigidity Mg-Al magnesium alloy material.

[0023] The purpose of adding auxiliary elements in the present invention is to refine grains, improve the morphology and properties of C36 or C15 phases, enhance the interfacial bonding force between the reinforcing phase and the matrix, form new high-modulus phases, and improve corrosion resistance. The purpose of adding high-modulus reinforcing phases in the present invention is, on the one hand, to further enhance stiffness, and on the other hand, to improve the morphology and properties of C15 phases, promote the nucleation of C15 phases, inhibit the growth of C15 phases, or form a core-shell structure with high-modulus reinforcing phases wrapped by C15 phases to improve the interfacial bonding strength, etc.

[0024] The following further describes the present invention in conjunction with examples and drawings.

[0025] In the following examples, conventional gas-protected magnesium alloy melting methods and permanent mold casting are used to prepare ingots. Specifically, the preparation process of the ingots is as follows: Put magnesium ingots in a graphite crucible, and under the protection of a mixed gas of argon and tetrafluoroethane (volume ratio 95:5), first melt pure Mg. After pure Mg melts, add pure Al and stir well; after Al melts, skim the slag, add pure Ca, etc. (such as including auxiliary alloy elements or high-modulus reinforcing phases). Ordinary alloy elements can be added directly. For elements with a low density and high chemical activity like Ca, use a bell jar method to quickly immerse it below the liquid surface to prevent oxidation; for high-modulus reinforcing phases with a high melting point, use mechanical stirring to promote its uniform dispersion. The melt temperature when adding Ca is 650 - 700 °C; when adding Si, use Al-10Si master alloy, and the melt temperature is controlled at 650 - 700 °C; when adding SiC particles, first add them while mechanically stirring at a semi-solid temperature of 600 - 658 °C, with a stirring speed of 200 - 400 revolutions per minute for 15 minutes, and then mechanically stir at a liquid temperature of 658 - 750 °C for 15 minutes, with a stirring speed of 300 - 600 revolutions per minute; the pouring temperature is controlled at 650 - 830 °C. Due to the difference in the melting points of different alloys, the pouring temperature is selected 5 - 30 °C above the melting point. Pour the melt into a copper water-cooled mold, and an ingot is obtained after the melt solidifies.

[0026] Elastic modulus specimens are processed from the ingots by wire cutting and milling methods. The specimen size is 75 mm × 15 mm × 5 mm, and the elastic modulus is tested by the dynamic method described in GB / T22315-2008 "Test Methods for Elastic Modulus and Poisson's Ratio of Metallic Materials".

[0027] Example 1 Prepare three magnesium alloys with mass percentage compositions of Mg-24%Al-12%Ca, Mg-16%Al-12%Ca, and Mg-12%Al-12%Ca respectively, and test the room temperature elastic modulus of the magnesium alloys when the Ca content is 12% and the Ca / Al mass ratios are 0.5, 0.75, and 1 respectively.

[0028] Example 2 Prepare five magnesium alloys with mass percentage compositions of Mg-20%Al-15%Ca, Mg-24%Al-18%Ca, Mg-28%Al-21%Ca, Mg-32%Al-24%Ca, and Mg-36%Al-27% respectively. Test the room-temperature elastic modulus of magnesium alloys when the Ca / Al mass ratio is 0.75 and the Ca content is selected as 15%, 18%, 21%, 24%, and 27% respectively.

[0029] Name the alloy compositions in Examples 1 and 2 according to the magnesium alloy grade naming method of GB / T 5153-2016. The naming rule is AGXX, where A represents Al, G represents Ca, the first X represents the content of Al, and the second X represents the content of Ca. The test results of the elastic modulus are as Figure 1 shown. It can be found that when the Ca content is 12%, as the Ca / Al mass ratio increases from 0.5 to 1, the elastic modulus decreases from 52 GPa to 49 GPa, and the elastic moduli of the three alloys do not reach 55 GPa. When the Ca / Al mass ratio = 0.75, as the Ca content increases from 15% to 27%, the elastic modulus increases from 53 GPa to 63 GPa, and according to Figure 1 judgment, when the Ca content is greater than 15%, combined with alloying modification, plastic deformation, and artificial aging treatment, the elastic modulus of the alloy can be greater than 55 GPa. The metallographic microstructures of the above eight alloys are as Figure 2 shown. It can be found that when the Ca content is 12%, as the Ca / Al mass ratio increases from 0.5 to 1, the volume fraction of the C36 or C15 phase has a decreasing trend, resulting in a decrease in the elastic modulus; when the Ca / Al mass ratio = 0.75, as the Ca content increases from 15% to 27%, the volume fraction of the C36 or C15 phase increases, leading to an increase in the elastic modulus.

[0030] Example 3 On the basis of AG2418, 3% Si was added to prepare the AG2418 + 3wt.% Si alloy. As Figure 3 shown, a high-modulus phase of CaMgSi was formed in the microstructure. On the premise of maintaining a room-temperature elastic modulus of 57 GPa, from Figure 4 the polarization curves and corrosion current densities of the two alloys in 3.5% NaCl solution, it can be found that after adding Si to AG2418, the corrosion current density decreases from 1.43×10-3 A / cm2 to 4.64×10-4 A / cm2, and the corrosion resistance is significantly improved. The reason is that the CaMgSi phase can improve the compactness of the corrosion product film.

[0031] Example 4 Based on AG3224, 0.1 wt.% SiC particles with an average particle size of 0.8 μm were added to prepare 0.1% SiC / AG3224. On the premise of maintaining a room-temperature elastic modulus of 59 GPa as Figure 5 shown, it can be seen from the microstructure that the addition of a small amount of SiC particles can significantly refine the coarse primary C36 or C15 phase.

[0032] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the above embodiments have described the present invention in detail, those skilled in the relevant art should understand that the present invention can be modified or equivalently replaced. Any modification and partial replacement without departing from the spirit and scope of the present invention shall be covered within the scope of the claims of the present invention.

Claims

1. A high-rigidity Mg-Al magnesium alloy material, characterized in that: Contains main alloying elements Al and Ca, wherein the Ca content is 15 wt.%~30 wt.%, and the Ca / Al mass ratio is 0.4~1.

2. The high-rigidity Mg-Al magnesium alloy material according to claim 1, characterized in that: The Ca content is 15.5 wt.%~27 wt.%, and the total content of Al and Ca is ≥31wt.%.

3. The high-rigidity Mg-Al magnesium alloy material according to claim 1 or 2, characterized in that: The Ca / Al mass ratio is 0.

75.

4. The high-rigidity Mg-Al magnesium alloy material according to claim 1 or 2, characterized in that: The magnesium alloy material further comprises auxiliary alloying elements and / or a high modulus reinforcing phase.

5. The high-rigidity Mg-Al magnesium alloy material according to claim 4, characterized in that: The total content of the auxiliary alloy elements is ≤20wt.%; the high modulus reinforcing phase is one or more of SiC, Al2O3, ZrO2, TiC, carbon nanotubes, graphene, carbon fiber, ZrB2, TiB2, B4C, AlN, titanium and titanium alloys, and high entropy alloys.

6. The high-rigidity Mg-Al magnesium alloy material according to claim 5, characterized in that: The auxiliary alloying elements are one or more of Ag, Au, B, Ba, Be, Bi, Cd, Ce, Co, Cr, Cu, Fe, Ga, Ge, Hg, I, In, K, Li, Mn, Mo, Na, Nb, Ni, Os, P, Pb, Pd, Pt, RE, Rh, Ru, Sb, Sc, Se, Si, Sm, Sn, Sr, Ta, Te, Tn, Tl, Ti, U, V, W, Y, Zn, and Zr.

7. The high-rigidity Mg-Al magnesium alloy material according to claim 5, characterized in that: The high modulus reinforcement phase is in the form of particles, fibers, sheets or whiskers.

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