Tailoring of Processing Parameters, Dendritic Microstructure, Si/Intermetallic Particles and Microhardness in As-cast and Heat-Treated Samples of Al7Si0.3Mg Alloy

Abstract

In this work, solidification and T6-heat treatment experiments were performed with the Al7Si0.3Mg alloy in order to investigate the effect of processes parameters on the microstructure and microhardness (HV). A directional solidification device was used, and the solidification thermal parameters investigated were the growth and cooling rates (VL and TR). The heat treatment applied was the T6 (T6-HT), under the following conditions: solution treatment for 3 h at 520????????2 ??C, followed by quenching in warm water (70????????20 ??C), aging for 1, 2, 3 and 4 h at 155????????2 ??C and air-cooling. The microstructure observed in both as-cast and T6-heat treated samples is composed of a primary phase consisting of an Al-rich dendritic network and secondary eutectic phases, located within the interdendritic regions, formed by Si and Mg2Si particles and Fe-intermetallic phases. The dendritic microstructure was characterized by secondary dendritic spacing (??2) and, for both investigated samples, a single mathematical expression was proposed on the ??2 dependence with the position in the ingot. Spheroidized-like eutectic Si particles have been found in both analyzed samples for finer microstructures. Elements quantitative and qualitative microanalysis by SEM/EDS as well as HV measurement at the dendritic and interdendritic regions attest to the effectiveness of the T6-heat treatment. It is highlighted in this work that mathematical expressions have been proposed to characterize the HV dependence on aging time.