Microstructure Evolution of 7055-T76 Aluminum Alloy in the Coupled Thermal-Mechanical Severe Plastic Deformation Process of Friction Stir Welding: Grains, Texture, and Precipitates

Abstract

In this study, the microstructure evolution of 7055-T76 aluminum alloy in the coupled thermal-mechanical severe plastic deformation process of friction stir welding was investigated. Significant differences in the grain size, texture, and precipitates among different zones in FSWed joint were determined by the complex coupled thermal-mechanical effect. The base material (BM) was mainly composed of deformation grain and Brass and S texture with a sizeable η phase. The growth, partial recrystallization, and fully recrystallization of grains occurred in heat affected zone (HAZ), thermo-mechanical affected zone (TMAZ) and nugget zone (NZ), respectively. The growth, re-dissolution, and re-precipitation of nano-precipitates occurred in HAZ and NZ, respectively. It was found that superior synthetic microstructure characteristics were obtained in NZ. The NZ of FSWed joint was composed of refined recrystallized equiaxed grains about 1.4 μm and textures of Goss {110} < 001 > , R {124} < 211 > , and P {011} < 112 > with the weakest intensity. The precipitates were fully re-dissolved, and little η′ precipitates re-precipitated in NZ under deformation and high-temperature interaction. In addition, many high-angle grain boundaries existed in the BM and NZ.