Effects of Friction Stir Additive Deposition Process Under Different Cooling Conditions on the Microstructure and Mechanical Properties of 2195 Al-Li Alloy

This study investigates the effects of air cooling and water mist cooling on the microstructure and mechanical properties of friction stir additive manufactured Al-Cu-Li alloy. The results show that under air cooling, coarse grains (average 15.37 μm) form, accompanied by coarse θ phase (Al2Cu), S phase (Al2CuMg), and Fe-containing brittle intermetallic compounds. A strong texture is observed (P_max = 6.45), and the tensile fracture surface exhibits a mixed ductile–brittle fracture mode with the coexistence of cleavage facets and dimples. The tensile strength, yield strength, and elongation are 325 MPa, 165 MPa, and 21%, respectively. Water mist cooling significantly refines the grain size (average 5.15 μm), weakens the texture (P_max = 5.41), suppresses the formation of detrimental Fe-containing phases, and promotes the precipitation of fine, dispersed θ phase and T1 phase (Al2CuLi) (~200 nm). The fracture surface transforms into a uniformly dimpled ductile fracture. Mechanical properties are simultaneously improved: tensile strength reaches 348 MPa (+7%), yield strength 182 MPa (+10%), and elongation 24.5% (+17%). Rapid cooling achieves a synergistic optimization of strength and ductility through grain refinement strengthening, precipitation strengthening, and elimination of harmful phases.