An investigation on low energy pulsed laser shock peening on mechanical and surface characteristics of aa7075 t651 alloy

Abstract

A high strength coupled with low density (2840 kg/m3) makes AA 7075 alloy a suitable candidate for producing aerospace components, marine applications and structures subjected to static and dynamic loads. In particular, AA 7075 T651 alloys are widely utilized in the upper wing cover, fuselages of aerospace industries and marine structures with corrosive atmosphere. This entails improving surface properties such as hardness, wear-resistance and chemical stability to overcome the breakdown of the passive film by a high concentration of chlorides. Numerous surface treatment techniques are available to improve the wear and corrosion resistance, out of which, Laser Shock Peening (LSP) provides useful features than other techniques viz., deeper compressive residual stress, less surface damage, better grain refinement and above all without changing its chemical composition. Though many researchers have examined LSP on aluminum alloy, only a lesser attention has been paid to the application of low energy pulsed LSP on AA 7075 T651 and its consequent improvement in wear and corrosion characteristics. The high energy pulsed LSP are vulnerable to the creation of surface undulations and reliability issues. Hence,the employment of low energy pulsed LSP is imperative to improve the surface properties, which is the subject matter of this investigation.In the present investigation, a Q- switched Nd:YAG laser having different low pulse energies of 200mJ, 300mJ, and 400 mJ with black paint and water as the ablative layer and confinement medium, respectively are used to study the variations in the mechanical properties and surface characteristics of AA 7075 T651. The microstructural variations, plastic strain, dislocation density, surface roughness and wettability characterizations are carried out using an Optical microscope, Scanning Electron Microscope, X-ray diffraction (XRD), Talysurf roughness tester and Goniometry instrument, respectively. The 400 mJ used specimen gives 355.917 E-04 microstrain and 1.92 and#956;m average surface rou