Effect of cooling rate, strontium modification, melt thermal treatment and solution heat treatment on the eutectic silicon particle characteristics and tensile properties of A356 alloy.

摘要

The effect of solution heat treatment on the tensile properties of the various A356.2 alloy castings can be summed up as follows. The yield strength of the various A356.2 alloy castings is significantly improved after 8 h solution heat treatment due to the precipitation of Mg2Si. The yield strength remains more or less the same with further increase in solution treatment time to 80 h. The UTS is also greatly improved within the first 8 h of solution heat treatment and then remains at the same level as solution time increases up to 80h. The improvement is attributed to Mg2Si precipitation, dissolution of Si within the Al-matrix, and change in the Si particle morphology (spheroidization). The ductility of the NM, SH, and MTT processed A356.2 alloy castings can be improved considerably with solution heat treatment ( e.g. from ∼6% in the non-modified casting in the as-cast condition to ∼10% after 80 h solution treatment). However, that of the SrM and SrMTT processed castings shows no remarkable improvement. (Abstract shortened by UMI.)