Microstructure And Mechanical Property Of The As-rolled Mg-Al-Sn-Si Alloy

Due to its high specific strength and specific stiffness, facility in cutting machining,good dimensional stability as well as good performance in vibration reducing, magnesium alloys has been widely used in various fields such as aerospace, automobile manufacture and communication equipments and so on. But the poor performance in tensile strength and high temperature creep resistance has restricted its further development and application in industry.This paper prepared two alloys systems, namely Mg-3Al-3Sn-lZn-0.5Si (ATZS3310.5)and Mg-3Al-3Sn-lZn-lSi (ATZS3311), by gravity casting. Optical microscope, X-ray diffraction and Universal test tensile machine are employed to test the microstructure, phase composition and mechanical properties of both alloy systems in both as-cast condition and solid-solution state. Then optimization in solid-solution process and rolling mill practice were carried out to investigate the refinement mechanism and spheroid zing mechanism of the Mg2Si second phase.The results indicated that both ally systems were composed of ?-Mg?Mg17Al12?Mg2Sn?MgZn and Mg2Si five phases. The tensile strength of ATZS3310.5 and ATZS3311 were 124MPa and 145Mpa with elongation rate of 16.1% and 14.0% respectively. This comparatively lower mechanical property were mainly imputed to the Chinese character like Mg2Si phase, which dissevered the matrix magnesium alloys, causing significant deterioration in strength and toughness of the alloys.Then three different solid-solution process were proceeded on both alloy systems. The subsequent characterization in microstructure and mechanical properties indicatied that alloys after successive heat treatment of soaking at 415? for 16h, soaking at 450 ? for 8h and water quenching exhibited best properties. Alloys after solid-solution were mainly made up of a-Mg and Mg2Si phases and modicum Mg2Sn phase. The Chinese character like Mg2Si phase was refined to some degree with small amount spheroid zed. The tensile strength and elongation were both improve compared with the as-cast alloys.The rolling mill process also made a difference in the mechanical properties of alloys.Rolling at the temperature of 400 ? with 10% per pass reduction and 80% total pass reduction, the tensile strength of the ATZS3310.5 and ATZS3311 could be obtained 286 MPa and 318MPa high with elongation rate of 18.6% and 18.3% respectively. Annealing at 300? for 1h lowered the tensile strength but improved the elongation rate. Compared with the AZ31 alloys without Sn and Si elements, the creep resistance at 150? and 200 ? of the alloys this paper studied have been enhanced remarkably.