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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。
The effects of on-line quenching, off-line solution treatment (rapid cooling in water at 420 ℃ × 1 h) and aging treatment (190 ℃ × 4 h air cooling) 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-cast AZ91D alloy, but the solution hardness decreases after the off-line solution treatment. The microstructure of AZ91D alloy is basically the same as AZ91D after in-line quenching and aging treatment, And β-Al12Mg17 composition. During the cooling process of die-casting magnesium alloy, quenching on-line abruptly decreases the temperature and enhances the effect of Al element solid solution strengthening. However, the aging treatment re-precipitates and refines the grains by Al12Mg17 decomposition and enhances the effect of fine grain strengthening. Although the effect of solid solution strengthening of Al12Mg17 decomposed after the solution treatment is off-line, the grain boundary strengthening phase decreases greatly, resulting in the decrease of alloy hardness.