Influence of laser shock peening on the coefficient of thermal expansion of Al (7075)-based hybrid composites

Abstract Integration of laser shock peening (LSP) and friction stir welding (FSW) was conducted for TiC strengthening on 7075 aluminum (Al) alloys. During FSW, TiC nanoparticles were mixed by using a stir pin to obtain TiC coating with FSWed joints. Nanocrystallines on the surface of Al-based hybrid composites with high-density dislocation were generated through LSP. Microstructural variables, including dislocations and precipitates of the different treatment specimens, were characterized through transmission electron microscopy and X-ray diffractometry. Thermal expansion of cylindrical treated samples was measured from room temperature to 300 °C. The coefficient of thermal expansion (CTE) value of the LSPed samples with TiC decreased by approximately 30% compared with that of the as-FSW sample. Differential scanning calorimetry (DSC) provides insights into the thermal expansion and strengthening mechanisms of LSP. These conditions were mainly caused by the acceleration of precipitated phase transformation from metastable η′ to stable η, resulting in the negative growth of the lattice constant of Al matrix and a decrease in CTE. In addition, the low CTE and dislocation pinning are important in providing a significant synergistic contribution to retard the thermal expansion of Al (7075)-based hybrid composites.