Effect of ultrasonic surface rolling on the microstructure and mechanical properties of 2195 Al-Li alloy fabricated by laser powder bed fusion in various build directions

To address the challenges of poor forming quality in the laser additive manufacturing of lightweight alloys, this paper explores an approach that integrates a laser additive manufacturing strategy for lightweight alloys with surface deformation strengthening. The study investigates the combined effects of build direction (BD) and ultrasonic surface rolling (USR) on the microstructure, residual stress, and mechanical properties of 2195 Al-Li alloy processed by laser powder bed fusion (LPBF). The results indicate that changes in BD significantly affect the growth direction of columnar grains (CGs) in the formed specimens and lead to the formation of a gradient microstructure with different characteristics under the influence of USR. When BD is 0 degrees, the post-USR specimen exhibits the most significant deformation strengthening effect, with the high dislocation density reaching depths of up to 720 mu m and compressive residual stress amplitudes up to -159 MPa. When BD is 90 degrees, the sample shows excellent tensile performance with an ultimate tensile strength (UTS) of 386 MPa and an elongation (EL) of 8.2 %. After USR treatment, the UTS of the sample increases to 438 MPa, but the EL decreases to 5.1 %. CGs exhibit varying deformation resistances in different directions, thereby influencing the deformation strengthening effect of USR and altering the crack propagation mechanism during the tensile process.