由于国家对“轻量化”发展的需求，产品和商品的轻薄化已经渗透到诸多行业和领域中，镁及镁合金由于其低密度、高比强度和比刚度、易回收等优点，在航空航天、汽车和电子领域被广泛应用，但目前仍存在诸多限制因素，如材料强度不足、加工性差，而半固态注射成形制得的镁合金件具有孔隙率低、机械性能优良等优点，可以获得近终态成形的镁合金零件。近年来，半固态注射成形已被积极引入商业应用。

本文采用半固态注射成形法制备镁合金，研究固溶、时效处理对合金显微组织、硬度、力学性能及耐腐蚀性能的影响规律，从而确定较佳的热处理工艺参数。针对铸造合金存在的组织缺陷，通过对合金进行低温二次热挤压，分析其对合金显微组织及力学性能的影响；并基于Johnson-Cook硬化模型对最佳热处理工艺的半固态注射成形镁合金多应变率下的力学性能进行试验及模拟，通过实验，得出以下结论。

本实验制得的半固态注射成形镁合金，由α-Mg基体与晶界处的α-Mg和β-Mg₁₇Al₁₂相的共晶组织组成。与压铸镁合金相比，合金出现晶粒细化，平均晶粒尺寸为20-30μm，可获得质量良好的显微组织，并出现类似球状固体组织；通过热处理得到，镁合金第二相的析出量与时效温度和时间呈正相关，第二相在晶粒内部和晶界处均匀析出。当时效处理温度过高时，第二相的析出不均匀；且当时效时间过长时，合金中析出的相也趋于粗化和聚集经过固溶、时效处理后，耐腐蚀性能先提高后降低。由此得到镁合金中β–Mg₁₇Al₁₂的存在、数量和均匀性对其耐腐蚀性能有较大的影响。

为减少合金的铸造缺陷，对合金进行二次低温热挤压处理，由于热挤压变形时动态再结晶的作用，晶粒大小较热挤压处理前并未出现明显的粗化现象；同时经过热处理后挤压态镁合金仍表现出较为优异的抗拉强度及硬度；基于镁合金应变率拉伸试验及拟合结果发现，随着应变率的增加，合金表现出较强的应变速率强化效应，使镁合金发生拉伸硬化，影响镁合金拉伸性能；同时镁合金在0.01-0.5s^-1有较好的动态拉伸性能。

经试验研究，发现半固态注射成形镁合金的力学性能优于压铸成形镁合金；半固态注射成形镁合金较佳的固溶处理工艺为390°C保温8h；较佳的时效处理工艺为170°C保温12h；同时经过热处理后，合金的力学性能和动态拉伸性能得到提高。并且经过二次热挤压后可进一步提升其性能。

Magnesium alloys have many advantages, such as low density, high specific strength and stiffness, good casting properties, and easy recycling. However, the current commercial magnesium alloys are limited by the lack of material strength and processing difficulties. Compared with cast magnesium alloys, semi-solid injection molded magnesium alloys have the advantages of low porosity and excellent mechanical properties. Also, they can obtain near-net shape machined magnesium alloy parts, which have been actively introduced for commercial use in recent years.

In this paper, magnesium alloys were prepared by semi-solid injection molding. Different heat treatment processes investigated the alloys' microstructure, hardness, mechanical properties, and corrosion resistance in different states. The optimal heat treatment process for the semi-solid injection molding of magnesium alloy was discussed. The effects of low-temperature secondary hot extrusion on the microstructure and mechanical properties of the alloy were analyzed for the structural defects existing in the cast alloy; based on Johnson-Cook hardening model, the mechanical properties of the semi-solid injection molded magnesium alloy with the optimal heat treatment process at various strain rates were tested and simulated. Through the experiments, the following conclusions were drawn.

The semi-solid injection molded magnesium alloy produced in this experiment consists of eutectic organization of α-Mg and α-Mg and β-Mg₁₇Al₁₂. Compared with the die-cast magnesium alloy, the alloy appeared grain refinement with an average grain size of 20-30 μm, which could obtain a good quality microstructure and a spherical solid-like organization; obtained by heat treatment, the precipitation of the second phase of the magnesium alloy was positively correlated with the aging temperature and time, and the second phase was uniformly precipitated inside the grains and at the grain boundaries. When the aging treatment temperature is too high, the precipitation of the second phase is not uniform; and when the aging time is too long, the precipitated phase also tends to coarsen and gather in the alloy after solid solution and aging treatment, the corrosion resistance first improves and then decreases. Thus, the presence, quantity and uniformity of β-Mg₁₇Al₁₂ in magnesium alloy have a great influence on its corrosion resistance.

In order to reduce the casting defects of the alloy, the alloy for the second low temperature hot extrusion treatment, due to the role of dynamic recrystallization during hot extrusion deformation, the grain size than before the hot extrusion treatment did not appear obvious coarsening phenomenon; at the same time after heat treatment extrusion state magnesium alloy still shows more excellent tensile strength and hardness; based on magnesium alloy strain rate tensile test and fitting results found that, with the increase of strain rate, the alloy shows With the increase of strain rate, the alloy showed a strong strain rate strengthening effect, so that the magnesium alloy tensile hardening, affecting the magnesium alloy tensile properties; at the same time, the magnesium alloy in 0.01-0.5s^-1 has a good dynamic tensile properties.

After the experimental study, it was found that the mechanical properties of semi-solid injection molding magnesium alloy were better than those of die-casting magnesium alloy; the better solution treatment process for semi-solid injection molding magnesium alloy was 390°C for 8h; the better aging treatment process was 170°C for 12h; meanwhile, the mechanical properties and dynamic tensile properties of the alloy were improved after heat treatment. And after the second hot extrusion can further improve its performance.

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