Microstructure And Mechanical Properties Of Several Heat Resistant Magnesium Alloys

In order to optimize the performance of heat resistant magnesium alloy,Mg-Al-Mn-Zn-Sn-Sr-Ca and Mg-Sn-Si-Sr-Al-Zn alloys were designed based onMg-Al-Mn-Zn-Sn-Sr alloy and Mg-Sn-Si-Sr alloy in this paper. The phase constituentand microstructure of the alloys were analyzed by using x-ray diffractometer, opticalmicroscopy, scanning electron microscopy and energy disperse spectroscopy,respectively. The mechanical properties of the alloys were tested by electronic universalmechanical testing machine. The fracture surfaces were analyzed by using scanningelectron microscopy. The main conclusions obtained are summaried as follows:The microstructure of the as-cast Mg-6Al-0.3Mn-0.5Zn-1.5Sn-0.3Sr-xCa（x=0,0.5,1.5,2.5） alloys are composed of Mg₃₂（Al,Zn）₄₉、MgSnSr、Al₈Mn₅and some other secondphase in the α-Mg matrix. The as-cast Mg-6Al-0.3Mn-0.5Zn-1.5Sn-0.3Sr-0.5Ca alloy iscomposed of Mg₃₂（Al,Zn）₄₉、MgSnSr、Al₈Mn₅and Al₄Ca phase. As the adding of Caelement, the Al₄Ca phase is formed compared with the alloyMg-6Al-0.3Mn-0.5Zn-1.5Sn-0.3Sr. The formation of CaMgSn phase is promoted whenthe content of Ca element is increased from0.5%to1.5%. The Mg₂Ca phase is formedwhen the content of Ca element is increased to2.5%. TheMg-6Al-0.3Mn-0.5Zn-1.5Sn-0.3Sr-1.5Ca alloy has the best mechanical properties. Itstensile strength, yield strength and elongation rate are178MPa,102MPa and5.38%atroom temperature. Its tensile strength, yield strength and elongation rate are145MPa,88MPa and6.74%at high temperature.For as-cast Mg-5Sn-2Si-2Sr-3Al-xZn（x=3,6,9） alloys, the adding of Al and Znelement can promote the formation of Mg₃₂（Al,Zn）₄₉phase remarkable compared withMg-5Sn-2Si-2Sr alloy. With the increase of Zn content，the content of Mg₃₂（Al,Zn）₄₉phase decreased, while the content of Mg₂Si and Mg₂Sn phase increases gradually. TheMg-5Sn-2Si-2Sr-3Al-6Zn alloy has the best mechanical properties. Its tensile strength,yield strength and elongation rate are165MPa,105MPa and6.27%at room temperature. Its tensile strength, yield strength and elongation rate are151MPa,94MPa and6.38%athigh temperature.Heat treatment improved the performance of the as-cast alloys significantly. Themost suitable heat treatment process of Mg-6Al-0.3Mn-0.5Zn-1.5Sn-0.3Sr-1.5Ca issolution for24h at400℃, and aging for24h at200℃. The tensile strength, yield strengthand elongation at room temperature are185MPa,109MPa and6.76%, respectively. Thetensile strength, yield strength and elongation are149MPa,83MPa and6.8%at hightemperature. The most suitable heat treatment process of Mg-5Sn-2Si-2Sr-3Al-6Zn issolution for20h at420℃, and aging for16h at180℃. The tensile strength, yield strengthand elongation are173MPa,108MPa and6.35%at room temperature. The tensilestrength, yield strength and elongation are168MPa、99MPa and6.42%at hightemperature.