Effect of laser shock peening on the microstructure and corrosion resistance in the surface of weld nugget zone and heat-affected zone of FSW joints of 7050 Al alloy

Abstract

Laser shock peening (LSP) was used to strengthen the surface properties of friction stir welding (FSW) joint for 7050-T7451 aluminium alloys. The microstructure, precipitates, dislocations and electrochemical corrosion properties in the surface of weld nugget zone (WNZ) and heat-affected zone (HAZ) of FSW joints were analyzed. The microstructure experienced an obvious change in the cross-section region close to the upper surface of WNZ and HAZ after LSP. The number of precipitates near the grain boundary increased obviously after the LSP. The dislocation in the shock region mainly shows the dislocation line, dislocation tangle, dislocation walls and sub-grain structure (Grain size 2–3 μm). The surface of as-received shows the highest corrosion potential (−0.835 V) in a 3.5% NaCl solution, and the corrosion potential in the surface of WNZ (−0.898 V) and HAZ (−0.932 V) after LSP is higher than the one before LSP. Grain refinement, precipitates and high density dislocation could play an important role to improve the corrosion resistance in the surface of WNZ and HAZ after LSP.