Effect of splat cooling on microstructures and mechanical properties of friction stir welded 2195 Al–Li alloy

Abstract

To achieve high-strength joints of 2195 Al–Li alloy, a novel splat cooling assisted friction stir welding (SCaFSW) was proposed. The microstructures and mechanical properties of conventional friction stir welded and splat cooling assisted friction stir welded 2195 Al–Li alloy were comparatively studied. The work revealed that using splat cooling in friction stir welding could reduce the welding temperature and fluidity of the plastic materials which lead to a rough weld surface in the SCaFSW, and even lead to the formation of void defects at the rotation speed of 400 rpm. However, finer grain size and higher dislocation density were observed in the weld nugget zone of the SCaFSW joint compared to conventional FSW. Furthermore, the application of splat cooling in FSW suppressed the dissolution of precipitates into the matrix during welding, resulting in some coarse residual precipitates in the weld nugget zone of SCaFSW joints. In addition, splat cooling in FSW could significantly increase the tensile strength of defect-free 2195 Al–Li alloy joints but decrease the elongation of the joint. The maximum tensile strength of the SCaFSW joint reached 502.7 MPa, which is 93% of the base material.