Local microstructure evolution and mechanical performance of friction stir additive manufactured 2195 Al-Li alloy

The present investigation is mainly focused on friction stir additive manufactured (FSAM) 2195 Al-Li alloy in aspects of localized microstructure evolution and mechanical performance. Characterization of the localized microstructure was conducted by optical microscope (OM), electron back scattered diffraction (EBSD) and transmission electron microscopy (TEM) techniques, and mechanical properties were evaluated based on micro-hardness and tensile testing measurements. Results showed a build of multilayered stack of 2195 aluminum lithium alloy was fabricated using FSAM via multi-pass processing. Defects such as voids or kissing bond were not identified, and fine equiaxed grains were observed in the nugget zone (NZ). The decrease of average grain size and low angle boundaries (LABs) along the depth of the NZ was attributed to repetitive stirring action of the rotating tool. Distribution of precipitation phase is mainly determined by the thermal cycle. Numerous T1 and θ′ precipitates were identified in the base material (BM), which are beneficial to improve material hardness and thus strength. These precipitates were dissolved in NZ and thermo-mechanically affected zone (TMAZ), and coarsen in heat affected zone (HAZ), which caused loss of hardness and strength. Similarly, precipitate morphology, size, and distribution are different in the built direction. Excellent tensile strength and elongation were identified in the NZ, which is attributed to fine grains and desirable precipitate characterization.