研究在线淬火、离线固溶处理（420℃×1 h在水中快冷）和时效处理（190℃×4 h空冷）对压铸AZ91D镁合金组织及硬度的影响。结果表明：在线淬火和离线的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硬度下降;在线淬火和时效处理后合金的组织与压铸AZ91D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淬火使温度急剧降低,增强了Al元素固溶强化的效果;而时效处理通过Al12Mg17分解后重新析出并细化了晶粒,增强了细晶强化的效果。离线的固溶处理Al12Mg17分解后虽然固溶强化效果增强但是晶界强化相大幅减少,导致合金硬度降低。
Effects of on-line quenching,off-line solution and aging heat treatment on microstructure and hardness of AZ91D die-casting alloy were investigated by means of OM,SEM,EDS analysis,DTA,XRD and hardness test.Brinell hardness of the die casting AZ91D alloy increases by on-line quenching and off-line aging treatment but decreases after off-line solution treatment.It is found that the microstructure of on-line quenched and off-line aged AZ91D magnesium alloy die casting is similar to that of die casting AZ91D alloy that consists of α-Mg and β-Al12Mg17.The precipitation of Al element is prevented by on-line quenching during solidification,so that the effect of solid solution strengthening is enhanced.The β-Al12Mg17 phase is dissolved in matrix and then precipitates along grain boundary after off-line solution and aging treatment,leading to microstructure refinement of AZ91D alloy and enhancing the effect of precipitation hardening.The hardness of die casting AZ91D alloy is reduced due to the decrease of β-Al12Mg17 phases as grain boudary strengthing phase by dissolution of the phases into matrix after off-line solution treatment.
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