Evaluation of the Effect of Melt Thermal Treatment on Microstructure and Mechanical Properties of Al–7Si Alloy

Abstract

The objective of this research was to investigate the effect of melt thermal treatment on microstructure and mechanical properties of Al–7Si alloy. Various characterization techniques and testings such as optical microscopy, scanning electron microscopy, tensile test and hardness test were carried out to evaluate the samples. The results showed that the melt thermal treated alloys have a more refined structure than that of the unrefined and chemically refined alloys. This led to a considerable improvement in tensile strength, hardness and ductility in the melt thermal treated alloys. The ultimate tensile strength, hardness and elongation of the only melt thermal treated alloys are observed to 153 MPa, 82 HRB and 14.8%, respectively, compared to 143 MPa, 72 HRB and 13.1% in the case of unrefined alloy. In the final microstructure of the melt thermal treated Al–7Si alloy most of the primary dendritic arms were found to be broken, which is an evidence of grain refinement. Besides, melt thermal treated alloy was observed to show refined Si to a certain extent. The average length of eutectic Si was lesser in case of the sample that had undergone both melt thermal treatment and Sr-modification than the only Sr-modified alloy.KeywordsMelt thermal treatmentMicrostructureAl–7Si alloyGrain refinerGrain modifierEutectic Siα-Al dendritic