Impact of cold spraying on microstructure and mechanical properties of optimized friction stir welded AA2024-T3 joint

The tensile properties of friction stir welded AA2024-T3 joints at the rotation speed range of 600-900 rpm and a constant welding speed of 200 mm/min were summarized, finding that the optimized rotation speed is 600 rpm which yield a maximum tensile strength of 420 MPa. Subsequently, an aluminum coating was deposited on the optimized joint surface by cold spraying (CS). The microstructural evolution in the layer near the surface of the coated joint was investigated by a combination of transmission electron microscopy, electron back-scattered diffraction and differential scanning calorimetry. The results show that the CSed joint exhibits significantly enhanced tensile strength, microhardness and fatigue life. This improvement is attributed to refined grains with a higher number of Guinier-Preston-Bagaryatsky (GPB) zones, finer and more S phases, and lower residual stresses due to the heat flow and shot peening effects by the CS on the layer near the surface. CS is shown to be an additional technique to enhance the mechanical properties of FSWed joints whilst providing corrosion protection for them.