Effect of post-processing heat treatment on microstructure and microhardness of water-submerged friction stir processed 2219-T6 aluminum alloy

The effect of post-processing heat treatment on the microstructure and microhardness of water-submerged friction stir processed 2219-T6 aluminum alloy was investigated. The microstructure was characterized using optical microscopy, scanning electron microscopy, and transmission electron microscopy. Two types of heat treatments, aging treatment and solutionizing followed by water quenching and aging treatment, were applied to the processed samples. The solutionizing followed by water quenching and aging treatment resulted in the abnormal grain growth in the stirred zone as well as the homogenous microhardness increase. The post-processing aging treated samples showed coarsened equilibrium precipitates and no re-precipitation, which led to the further decrease of the microhardness.