Evolution of dispersoids during multistep heat treatments and their effect on rolling performance in an Al-5% Mg-0.8% Mn alloy

The precipitation behavior of dispersoids in an Al-5% Mg-0.8% Mn alloy after various single-and multistep heat treatments and their effect on rolling performance were investigated. The results show a significant increase in the electrical conductivity and microhardness caused by the precipitation of submicron dispersoids after all heat treatments. In addition, the multistep heat treatments resulted in higher microhardness and a larger fraction of dispersoid zones than single-step treatments. Two types of Mn-bearing dispersoids with cube- and rod-like morphologies were identified. The low-temperature two-step heat treatment (275 °C/12 h + 375 °C /48 h) produced the highest number density of dispersoids with the finest size among all the studied heat treatments but severe defects were created during hot-rolling. The three-step heat treatment (275 °C/12 h + 375 °C/48 h + 500 °C/4 h) provided the best combination of dispersoid characteristics and rolling performance. The mechanical properties of rolled sheets subjected to the three-step heat treatment were improved compared to those treated using industrial homogenization treatment, owing to the higher number density and finer size of the dispersoids.