The effect of heat treatment on the microstructure and electrochemical corrosion behavior of multilayer AA6061 alloy fabricated by additive friction stir deposition

Multilayer AA6061 aluminum alloy components were successfully fabricated by additive friction stir deposition (AFSD). The effect of heat treatment on the microstructure and electrochemical corrosion behavior of the AA6061-T6 aluminum alloy components was studied. The average grain size in AFSD samples was 2.67 mu m, where 89.7 % of grains were smaller than 5 mu m. Abnormal grain growth was observed in the heat-treated AFSD (AFSD-HT) sample, and the average grain size of AFSD-HT sample was 592 mu m. In the base material (BM) sample, apart from the beta '' strengthening phases, hard-brittle Al5FeSi intermetallic compounds (IMCs) aggregated along the boundaries of the coarser grains. Due to the high temperature generated during the process of AFSD, beta '' phases dissolved into the matrix. After heat treatment, a larger amount of fine needle-like beta '' phases were reprecipitated in the AFSD-HT sample. Al5FeSi IMCs accelerated the corrosion of the Al matrix. Fine beta '' phases significantly inhibited the corrosion expansion to Al matrix and improved the corrosion resistance of AA6061 alloys.