Characterization of fine precipitates evolution in post ageing treatment after friction stir processed 7075Al Alloy

Abstract—The effect of post ageing treatment (140^oC for 2h) on the microstructure and mechanical behaviour of FSPed 7075 Al alloy has been studied by Optical microscopy (OM), Field emission scanning electron microscopy (FESEM), Differential scanning calorimetry (DSC), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and mechanical properties. Friction stir processing (FSP) is a solid-state surface modification technique to apply for cast aluminium alloys. FSP has a similar metal working principle like FSW (friction stir welding). The alloy has strong age-hardening response with scandium (Sc) inoculated Al-Zn-Mg alloy, on the other hand novelty of FSP only few studies have been carried out to the effect of post ageing treatment on the microstructure, size, morphology and fine dispersion of coherent Al₃Sc(L1₂) type precipitates or ή-phases and its mechanical properties of friction stir processed 7075 Al alloy. The FSPed enhances grain boundary (GB) formation and increases suitable sites for the precipitation of nucleation in post aged 7075 Al alloy. Themechanical properties have been evaluated such as proof strength (σ_{0. 2}) of 122. 9 MPa, ultimate tensile strength (σ_u) of 256. 4 MPa, ductility (δ) of 8. 6%, Vicker’s hardness in stir zone of 101 HV, strain hardening exponent (n) of 1. 82, and heat input during FSPed of 2. 15 kJ/mm, respectively.