Basic Investigation On Microstructure Controlling Of Mg-Al-Si And Mg-Zn-Al Based Magnesium Alloys

Mg-Al-Si and Mg-Zn-Al based alloys are thought as two kinds of potential magnesium alloys for the elevated temperature application. If the changs of microstructure for Mg-Al-Si and Mg-Zn-Al based alloys under the condition of different composites and/or treatment states are well known, the basic guidance for the development of new type Mg-Al-Si and Mg-Zn-Al based heat resistant magnesium alloys would be provided. However, all over the world the research about microstructure controlling of Mg-Al-Si and Mg-Zn-Al based heat resistant magnesium alloys are not quite systematic and perfect at present, so it has very important theoretical significance and practicable value to more investigate the microstructure of Mg-Al-Si and Mg-Zn-Al based magnesium alloys on the basis of these existing problems in microstructure controlling of the two kinds of magnesium alloys, then according to the research results obtained, the guidance basis of microstructure controlling of composition design and processing optimization not only for the exploitation of new type Mg-Al-Si and Mg-Zn-Al based heat resistant magnesium alloys but also for other heat resistant magnesium alloys, would be provided.Both the effects of Al content, trace antimony and RE, and solid solution treatment on the as-cast microstructure and/or heat treatment microstructure of Mg-xAl-0.7Si based alloys and the effects of Zn content, trace RE and/or TiC, and aging treatment on the as-cast microstructure and/or heat treatment microstructure of Mg-xZn-4Al based alloys were investigated by means of metallurgical phase analysis, scanning electron microscopy (SEM) analysis, energy diffraction (EDX) analysis, XRD analysis, and DSC in this paper, and following research results were obtained.The following research results about Mg-xAl-0.7Si based magnesium alloys were obtained:â‘ The as-cast microstructure of the experimental Mg-6Al-1Zn-0.25Mn alloy were composed of the primaryα-phase and Mg₁₇Al₁₂ phases whose shape were bone shape-like and layer shape-like, after adding 0.7%Si,0.4%Sb and 0.25%RE, Mg₂Si phase of Chinese script shape, Mg3Sb2 phase and a few Al₄Si₂Mn₂Y phase of needle shape which mainly distributed at grain boundaries, were found in the as-cast microstructure of experimental alloy, but The modification of Sb to the Mg2Si phase of Chinese script shape was not obvious. Furthermore, with the increasing of Al content, the amount of Mg₁₇Al₁₂ phase in the as-cast microstructure of Mg-(6～8)Al-1Zn-0.25Mn-...