Effect of Aging and Annealing Treatments on the Microstructural Behavior of Some Al-Si based Alloys

摘要

Al-Si foundry Alloys, of eutectic and hypo-eutectic compositions, are largely employed in the automotive industry because of their enhanced mechanical properties, their good flow and their relatively low melting points. We investigate in the present contribution, two different groups of alloys namely the AS13 (Al-13%Si in weight) and the AS10G (Al-10%Si-0.35%Mg in weight). Our study comprises two main parts in which, two types of heat treatments have been carried out: (i) Industrial heat treatments and (ii) isothermal annealing at 400°C and 500°C. The samples were characterized by optical microscopy, scanning electron microscopy and micro-hardness measurements. The microstructural characteristics of these alloys are mainly determined by their concentration in additives such as Mg. The AS13 alloys microstructure is characterized by the distribution and form of the eutectic silicon particles, whereas the AS10G alloys one is essentially marked by the presence of dendrites, Mg_2Si precipitates and some other intermetallic compounds. Most of these compounds and precipitates are formed after heat treatments. It was observed that some other compounds such as the iron-based intermetallics, which already form during solidification, where impossible to dissolve with solution treatment. These compounds were observed to prohibit Mg_2Si precipitates formation due to Mg solute trapping.