Effect of T6 heat treatment on microstructure and mechanical properties of Al–18Si–10Cu–10Ni–5Mn–5Mg alloy prepared by laser-directed energy deposition

Abstract

The new aluminum alloy Al–18Si–10Cu–10Ni–5Mn–5Mg (wt.%) prepared by laser-directed energy deposition (L-DED) process has excellent mechanical strength but poor ductility. In this paper, a T6 heat treatment is applied to it, aiming at the improvement of the material's ductility. The results show that after the T6 heat treatment, the original fine microstructure of the material is destroyed, and the phase composition changes. However, it is found that the formation of the nano-strengthened θʹ phase and the clear crystal orientation relationship between the θʹ phase and the α-Al matrix make the θ′ phase form a continuous grain boundary in the Al matrix, thus enhancing the strength and hardness of the alloy. It is worth noting that the microhardness is reduced slightly, but the residual stress is almost completely eliminated. The experimental results of mechanical properties show that the tensile strength and compressive strength of the material are reduced by 12 % and 17 % respectively after T6 heat treatment, but the ductility of the material is increased by 1.3 times, which is mainly attributed to the change of strengthening mechanism and the large and uniform second phase.