| Compared with engineering materials such as iron and steel, aluminum alloy, plastics and so on, magnesium alloy has more development potential because of its merits including lower density, higher specific strength and specific rigidity, better heat conductivity etc. And lost foam casting (LFC) is the process suiting with liquid precision forming of magnesium alloy parts because of its advantages including natural gas shielding in pouring and filling, precision forming, clean production and so on. Whereas general low mechanical property of magnesium alloy casting by LFC has limited its application and development further, for example, the AZ91 magnesium alloy being utilized over 90% in magnesium alloy castings, the tensile strength of LFC casting is only 130~140MPa and the elongation percentage is only 2~3%. It cannot satisfy the need for high performance castings. So it is very significant to study how to improve the mechanical property of magnesium alloy casting of LFC. Based on AZ91D which has been used widely, this paper had investigated the influence of mechanical vibration, Ce-Sb alloying, semisolid heat treatment to mechanical property of AZ91D casting by LFC aiming at the methods which can improve the casting mechanical property.It had been researched that the effect of solidification under mechanical vibration on the microstructure and mechanical property of AZ91D casting sample via LFC. The results showed that mechanical vibration could obviously refine the microstructure of AZ91D casting via LFC in different pouring temperatures; and in the same pouring temperature, the microstructure became finer and finer as the exciting force was increasing; whereas the changing law of the tensile strength and elongation percentage was up first and then down, and too powerful exciting force would make them decrease obviously. The effect of vibration solidification on the sample with different thickness showed that the more was the thickness, the more obvious was the vibration effect, and the finer microstructure and the more tensile strength and elongation percentage would be get.It had been researched that the effects of Ce-Sb compound addition on the microstructure and mechanical property of AZ91D casting sample by LFC. The results showed that Ce-Sb compound addition could obviously refine the microstructure of the sample, and the microstructure was becoming finer as the addition amount of Ce, Sb was increased, but the tensile strength and elongation percentage were the best when the addition amount was 0.4%Sb-1.0%Ce, respectively 182.23MPa and 2.53 %.It had been tested that the effects of Ce-Sb addition and mechanical vibration solidification on the microstructure and mechanical property of AZ91D casting sample by LFC. The results showed that the compound method was more effective to refine the microstructure and improve the mechanical property. The microstructure made by the compound method was finer than that only by mechanical vibration or only by Ce-Sb alloying; and the tensile strength and elongation percentage became higher, respectively 202.58MPa and 2.81%.It had been researched that the feasibility of applying semisolid heat treatment to the AZ91D castings by LFC, and the effects were also compared the semisolid isothermal heat treatment with T4 and T6 heat treatment to the microstructure and mechanical property of AZ91D casting sample via LFC. The results showed that the microstructure could be refined obviously and the property could also be improved by T4,T6 and semisolid heat treatment. The microstructure by T4 was oversaturatedα-Mg solid solution chiefly; and the microstructure by T6 had black near-molassedβ-Mg17Al12 precipitated phase at grain boundary except oversaturatedα-Mg solid solution; but spherical grain microstructure could be formed by semisolid isothermal heat treatment. The best technologic parameter of semisolid heat treatment to AZ91D via LFC was to be heated about 60 minutes at 530℃. The tensile strength and elongation percentage of the samples made by above three type heat treatment methods were respectively 181.25MPa and 4.35% by T4, 175.36MPa and 2.07% by T6, 213.17MPa and 4.11% by semisolid heat treatment.
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