Mechanical properties and deformation dependent microstructural aspects of laser shock peened 7075-T6 aluminum alloy without coating

This work presents the mechanical properties and elaborately discusses microstructural aspects of LSPwC (laser shock peening without coating) peened 7075-T6 aluminum alloy using the results coming from various characterization techniques such as surface roughness, Vickers microhardness, residual stress analysis, tensile test, X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and electron back scattered diffraction (EBSD). The possibilities and consequences of thermo-mechanical interaction, deformation behavior, grain refinement, fractional change of grain boundaries, compressive residual stress and nucleation of precipitates during LSPwC are discussed along with the underlying mechanisms. Microhardness increased by about 25% post LSPwC with a work hardened layer of more than 1000 mu m. Maximum compressive residual stress of -227 MPa (in sub-surface region of peened specimens) was induced with effective depth (i.e. thickness of compressive layer) of 900 mu m. The defect (dislocation) concentration, volume fraction of precipitates, area fraction of fine grains (of below 50 mu m) and number fraction of low angle grain boundaries (especially of 2 degrees-5 degrees misorientation) increased significantly after LSPwC. Besides, the effects of observed improvements (by LSPwC) in tensile behavior were also investigated. The near surface strengthening or modifications observed in this investigation are collectively attributed to LSPwC induced plastic deformation, compressive residual stress, additionally induced precipitates, grain refinement and increased fractions of LAGBs.