Effect of Solution Treatment on Microstructure, Mechanical Properties, and Strengthening Mechanisms of 6061 Aluminum Alloy

Different solution treatments for annealed 6061 aluminum alloy were performed using an orthogonal testing method. The effects of solution treatments on the microstructure and mechanical properties of the alloy were investigated by employing techniques such as electron backscatter diffraction and tensile tests. The effects of changes in the size and area fraction of the soluble phase on solid solubility, dislocation evolution, and recrystallization were explored. A microstructure evolution model for the solution-treated alloy was developed, and the contributions of different strengthening mechanisms were quantified. The results indicate that the optimal solution treatment parameters were treatment at 570 °C for 3 h, followed by water quenching. After treatment, Mg₂Si dissolves into the matrix, increasing the solid solubility and fraction of recrystallized grains while reducing the dislocation density. All solution-treated alloys, except those quenched in a furnace, displayed notable increases in strength with minimal loss in ductility. The water-quenched alloy exhibited the best overall mechanical properties, with the yield strength and ultimate tensile strength increasing by 139.4 and 128.1%, respectively, compared to those of the untreated alloy. Analysis of the strengthening mechanisms revealed that the primary contributors to improved alloy strength are dislocation and grain boundary strengthening.