Effects on microstructure and mechanical properties of aluminum alloy 6061 processed via underwater additive friction stir deposition

Abstract

Solid-state methods such as additive friction stir deposition (AFSD) have shown potential for the repair and bulk manufacture of precipitation-strengthened aluminum alloys, but most studies conducted with ambient air cooling have reported reductions in strength in the deposited material and underlying substrate. The present study investigates the effects of rapid heat dissipation in AFSD by conducting the entire deposition process underwater. Two depositions with the same process parameters and different cooling conditions are investigated, with subsequent comparisons highlighting differences in deposition morphology, mechanical properties, and microstructure. Microstructure characterization revealed significant grain refinement associated with the submerged cooling approach but a reduction in hardness and tensile strength compared to ambient conditions. The results of this study presented herein suggest that cooling the deposition in-situ can modify the deposition shape, induce less overall thermal degradation of the substrate, and produce superior grain refinement relative to ambient cooling conditions.