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研究在线固溶处理、离线固溶处理和时效处理对压铸AZ91D镁合金组织及硬度的影响。结果表明:在线淬火和离线时效处理可提高压铸AZ91D合金的布氏硬度,但是离线固溶处理使合金的硬度下降。通过X射线物相分析、光学显微组织分析、差热分析、扫描电镜及能谱分析,发现在线固溶和时效处理后合金的组织与压铸AZ91D的基本相同,仍由α-Mg及β-Al12Mg17组成。在压铸镁合金冷却过程中,在线固溶处理使温度急剧降低从而阻止了β-Al12Mg17相的继续析出,增强了Al元素固溶强化的效果。时效处理后,Al12Mg17从Mg的过饱和固溶体中析出并细化组织,改善了细晶强化的效果。离线的固溶处理使Al12Mg17分解,导致其固溶强化效果得到增强但是晶界强化相大幅度减少,从而使合金的硬度降低。
The effects of on-line solution treatment, off-line solution treatment and aging treatment on the microstructure and hardness of die-casting AZ91D magnesium alloy were investigated. The results show that the on-line quenching and off-line aging treatment can improve the Brinell hardness of the die-casting AZ91D alloy, but the solution treatment decreases the hardness of the alloy. By X-ray phase analysis, optical microstructure analysis, differential thermal analysis, scanning electron microscopy and energy spectrum analysis, found that the solid solution and aging treatment of the alloy and die-casting AZ91D basically the same organization, still by the α-Mg and β- Al12Mg17 composition. In the cooling process of die-casting magnesium alloy, the solution treatment on-line abruptly decreases the temperature and prevents the continuous precipitation of β-Al12Mg17 phase, which enhances the effect of Al element solid solution strengthening. After aging treatment, Al12Mg17 precipitated from the supersaturated solid solution of Mg and refine the microstructure to improve the effect of fine grain strengthening. Off-line solution treatment Al12Mg17 decomposition, resulting in enhanced solid solution strengthening effect but significantly reduced grain boundary strengthening, so that the hardness of the alloy decreases.