Microstructure and Fatigue Performance of Hard Al Alloy Repaired by Supersonic Laser Deposition with Laser Shock Peening Treatment

Abstract

High quality repair of damaged components is critical for aircraft maintenance industry. Apart from fulfilling the dimensional requirement, restoring the fatigue performance of repaired parts has always been a challenging problem. In this paper, the notched hard Al alloy specimens were repaired through cold spray (CS) and supersonic laser deposition (SLD) coating techniques, followed by laser shock peening treatment. The influence of different processes on the microstructure, phase composition, crystallographic characteristics of deformed grains in the coatings was studied. The fatigue performance of repaired specimens was evaluated. The results show that no phase transformations of powder materials were found both in CS and SLD coatings. The sever plastic deformation of 7075Al alloy particles in CS and SLD processes resulted in a bimodal grain structure. The conduction of laser shock peening treatment on SLD coatings improved the structural homogeneity with the averaged grain size down to 0.8μm, where the localized dynamic recrystallization was responsible for such refinement. The fatigue limit of CS and SLD repaired specimen was 127±30Mpa and 143±19MPa, respectively, which was lower than that of original specimen. In contrast, the fatigue limit of laser shock peening treated SLD repaired specimen reached to 168±11Mpa, which exceeded that of original specimen. This is attributed to the enhanced cohesive and adhesive bonding strength of repaired coatings. Therefore, it provides a novel approach for high quality repair of damaged aircraft components.

Keywords: cold spray, Supersonic laser deposition, laser shock peening, coating, Repair, Fatigue