The Study On Heat-Resistant Magnesium Alloys Applied In Engine Block

AM-SC1(Advanced Magnesium-Sanf Casting Alloy1) is a new heat-resisting Mg-RE based alloy which has been widely applied in engine block. The wide application of AM-SC1is limited for the high cost of rare-earth elements. Considering the special function of Ca and Ti on grain refinement and performance improvement, it would be an effective way to decrease the cost of the alloy by replacing Nd and RE with Ca and Ti as addition.The experimental alloy was prepared by an ingot casting method and reinforced by T6heat treatment to investigate the effects of Ca and Ti on the microstructure and mechanical properties. The microstructure、phases and thermal stability were investigated by means of OM、SEM、XRD、DSC.The mechanical properties of the alloy were investigated by Brinell hardness、 tensile tests at room and elevated temperatures.The results show that as the addition of Ca is1.5%, the Mg-0.4%Zn-1.0%Zr-1.5%Ca-2.0%RE alloy shows the finest grain size, which also contributes to the highest hardness and strength of62.1HB and148MPa, respectively. After T6treatment (solid solution treatment at500℃for7h and aging treatment at200℃for20h), the morphologies of the phases in the alloys change from net-like to fine short-block and particle-like shapes, and its strengths at RT,175℃and200℃are correspondingly improved to186MPa,166MPa and140MPa, respectively. As the addition of Ti element is0.8%, the Mg-0.4%Zn-1.0%Zr-1.5%Ca-0.8%Ti alloy shows the finest grain size. And the hardness and strength reach to the maximum of57.9HB and145MPa. After T6treatment, the phases in the alloys change from continuous net-like to uniform block-like shapes, and the strength at RT,175℃and200℃are correspondingly improved to182MPa、169MPa and141MPa.