Microstructure and strength-conductivity synergy of Al-Mg-Si-Cu alloy sheets prepared via vacuum melting and thermo-mechanical treatment

Abstract

This work has investigated the response of microstructural evolution on the strength and electrical conductivity (EC) of vacuum melted Al-Mg-Si-Cu alloys during T6 heat treatment, cold rolling (CR) and re-aging (RA). The precipitation behavior of nano-scaled precipitates during thermo-mechanical treatment was revealed. The strength- conductivity improvement mechanisms of the alloy were discussed. The results showed that compared with the non-vacuum melting alloy, there were superior enhancements in the strength and EC of the alloy prepared by vacuum melting due to the high compactness. After T6 heat treatment, nanoscale β", Q' and L phases were precipitated in the alloy sheet. Owing to the increased dislocation density and precipitate dissolution during CR, the strength of the alloy sheet was improved, followed by a decrease in EC. After RA, a good combination of strength and EC of the alloy sheet was obtained, i.e., ultimate tensile strength and EC were 350MPa and 57.48% IACS, respectively, which was associated with the formation of nano-sized precipitates and the decrease in solute atom concentration. The precipitates volume, dislocation density, grain refinement and solid solubility during thermo-mechanical treatment were the main factors determining the strength and EC of the alloy. This work provides a strategy for the preparation of high strength-conductivity Al alloys.