Semisolid Microstructural Evolution And In:fluence Factors For The Mg-Al-Sn-Zn-Si Alloy

The as-cast Mg-3Al-3Sn-1Zn-1Si (ATZS3311) and Mg-6Al-3Sn-1Zn-1Si (ATZS6311)alloys were fabricated by means of permanent mold casting method. ATZS3311 and ATZS6311 alloy semi-solid billets were successfully fabricated by strain-induced melt activation (SIMA) process. The corresponding analysis and testing for the both alloys handled by different processes were investigated by means of optical microscopy (OM)analysis, differential scanning calorimeter analysis (DSC), X-ray diffraction (XRD) analysis,Scanning electron microscopy analysis (SEM).The effects of the different treatment processes on both ATZS3311 and ATZS6311 semi-solid alloy were investigated. According the experimental objectiv, the reasonable semi-solid isothermal heat treatment process were determined as follows: the ATZS3311 of 30% pre-deformation isothermally heat-treated at 605 ? for 20 min; and the ATZS6311 of 30% pre-deformation isothermally heat-treated at 580? for 15 min.There were three kinds of evolution mechanisms of ATZS semi-solid alloy organization,namely the a-Mg spheroidization, the formation of primary Mg2Si phase and the granulating of the Chinese character-like eutectic Mg2Si phase. The a-Mg spheroidization mechanism of ATZS prepared by SIMA was dominated by the dendritic fusion, and the infiltration-precipitation of the liquidoid on the subboundary also made a difference. The granulating of the Chinese character-like eutectic Mg2Si phase was mainly due to the infiltration-precipitation mechanism. The coefficient of the redistribution of A1 and splat cooling contributed to the precipitation of Si in semi-solid liquid into granulous nascent Mg2Si,by the former factor resulting in left- shift of Mg-Si eutectic composition dominantly and the latter one in right-shift auxiliarily.