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采用磁悬浮熔炼真空吸铸法制备了快速凝固态AZ91D合金,采用常规铸造法制备了普通铁模铸型浇注的不同成分的Mg-Al合金。通过OM、SEM、EDS及XRD等现代检测方法,分析了不同凝固条件下Mg-Al合金的组织形貌、相组成和腐蚀形貌,研究了冷却速度和元素微合金化对Mg-Al合金组织及腐蚀性能的影响。结果表明:磁悬浮真空吸铸快速凝固AZ91D合金的α-Mg枝晶明显细化,尺寸由200μm降到20μm左右。β-Mg17Al12相则沿晶界形成连续网状。添加微量Si元素,α-Mg枝晶尺寸略有下降,晶内出现汉字状的Mg2Si相,促进β相的网状化。加快冷却速率,增加Al含量,添加微量Si元素均能提高合金的耐蚀性能。铜模吸铸AZ91D合金的自腐蚀电位Ecorr比铸铁模铸AZ91D合金正移0.375V,自腐蚀电流降低了1个数量级。Mg12Al-0.7Si合金的Ecorr比Mg12Al合金的正移0.526V,自腐蚀电流密度比Mg12Al合金降低1个数量级,比AZ91D合金降低2个数量级。
The rapidly solidified AZ91D alloy was prepared by vacuum levigation of magnesia, and the Mg-Al alloy cast by ordinary iron casting was prepared by conventional casting method. The microstructure, phase composition and corrosion morphology of Mg-Al alloy under different solidification conditions were analyzed by modern testing methods such as OM, SEM, EDS and XRD. The effects of cooling rate and elemental microalloying on microstructures and mechanical properties of Mg-Al alloy And corrosion effects. The results show that the α-Mg dendrites of the rapidly solidified AZ91D alloy with magnetic suspension vacuum-suction casting are obviously refined with size reduced from 200μm to 20μm. β-Mg17Al12 phase along the grain boundary to form a continuous network. Adding a small amount of Si, the size of α-Mg dendrite decreased slightly, and the Chinese-shaped Mg2Si phase appeared in the crystal to promote the reticulation of β phase. Accelerate the cooling rate, increase the Al content, add trace Si elements can improve the corrosion resistance of the alloy. The self-corrosion potential Ecorr of copper die-sucking AZ91D alloy is 0.375V more positive than that of cast-iron die-casting AZ91D alloy, and the self-corrosion current is reduced by one order of magnitude. The Ecorr of Mg12Al-0.7Si alloy is 0.526V more positive than that of Mg12Al alloy, and the self-corrosion current density is one order of magnitude lower than that of Mg12Al alloy and about two orders of magnitude lower than that of AZ91D alloy.