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采用铜模喷铸技术制备出AZ91D镁合金非平衡凝固试样,并对其热稳定性进行了研究。采用光学显微镜、扫描电镜、能谱分析仪及维氏显微硬度计对不同温度热处理镁合金的晶粒形貌、溶质含量及显微硬度变化进行对比研究。实验结果表明,当热处理温度200℃,保温时间240 min时,晶粒形貌未发生明显变化,但由于时效效应的存在,导致过饱和α-Mg固溶体中沉淀相析出,Al元素溶质含量有所下降,合金显微硬度略有升高。相同保温时间条件下,随热处理温度升高,β-Mg17Al12共晶相体积分数不断降低,固溶到基体中导致Al元素含量增加。与此同时,初生α-Mg相晶界逐渐清晰并发生明显的晶粒长大现象,合金显微硬度呈整体下降趋势。
The non-equilibrium solidified sample of AZ91D magnesium alloy was prepared by copper die casting technology, and its thermal stability was studied. The morphology, solute content and microhardness of the heat-treated magnesium alloy at different temperatures were compared by optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and Vickers microhardness tester. The experimental results show that when the heat treatment temperature is 200 ℃ and the holding time is 240 min, the grain morphology does not change obviously. However, due to the aging effect, the precipitated phase is precipitated in supersaturated α-Mg solid solution and the content of Al element solute Decline, the alloy slightly increased microhardness. Under the same holding time, with the increase of heat treatment temperature, the volume fraction of β-Mg17Al12 eutectic phase continuously decreased, and the content of Al element increased with solid solution into the matrix. At the same time, the grain boundaries of the primary α-Mg phase gradually became clear and obvious grain growth occurred, and the microhardness of the alloy showed an overall downward trend.