Thermal analysis and microstructures of modified grain-refined Al-7Si-Mg cast alloy

Abstract

This article aims to investigate the grain refining response of Sr-modified A356.2 alloy with various Al-Ti, Al-B and Al-Ti-B master alloys at different levels. Thermal analysis was used to evaluate the interactions between Sr and B, and between Sr and Ti. Microstructure was examined using optical microscopy and EPMA technique. Impact properties were evaluated for both as-cast and heat-treated conditions. The results reveal that adding B with levels higher than 0.1% leads to formation of particles containing predominantly B and Sr, such as SrB6. The Sr-B interaction may postpone grain refinement of the alloy containing 0.02-0.1%B. It is also observed that the Al-Ti-B and Al-4%B types of master alloy have a greater influence on the grain refining of the A356.2 alloy than does Al-10%Ti. The grain size of the alloy decreases rapidly with an increase in boron-content for the lower levels of boron addition.