The effect of heat treatment on the microstructure and mechanical properties of multilayer AA6061 alloy fabricated by additive friction stir deposition

Abstract

Multilayer AA6061 aluminum alloy components were successfully fabricated by the additive friction stir deposition (AFSD). The effect of heat treatment on the microstructure and mechanical behavior of the aluminum alloy components was studied. Due to dynamic recrystallization, AFSD AA6061 sample presented a 93.2% average reduction in grain size as compared to base material (BM) (∼ 39.13 µm). Abnormal grain growth was observed in the AFSD-HT sample, and the average grain size of AFSD-HT sample was 592 µm. There was an occurrence of texture formation in the AFSD and AFSD-HT samples, mainly due to severe shear deformation during AFSD process. The maximum texture density of AFSD-HT sample was increased to 17.84. In the BM sample, apart from the β" strengthening phases, hard-brittle intermetallic compounds of Al5FeSi aggregated along the boundaries of the coarser grains. Due to the high temperature generated during the process of AFSD, the β" strengthening phases dissolved into the matrix, and significantly reduced the strength and hardness. After heat treatment, the AFSD AA6016 alloy recovered 18% of its strength at a loss of 2.8% ductility. High density β" strengthening phases precipitated, resulting in increased strength and hardness.