Evaluation the effect of multi-pass friction stir processing on the wear, mechanical properties, and microstructure of the AA1050/ZrO2 surface nanocomposite

This work presents surface nanocomposites of aluminum alloy AA1050, reinforced with zirconium oxide (ZrO2) nanoparticles developed through multipass friction stir processing (FSP). This article attempts to study the effects of the number of passes on the wear rate, microhardness profile, tensile properties, and macrostructure of surface nanocomposites. The results demonstrate that an improved distribution of ZrO2 nanoparticles is obtained following each FSP pass, and that the number of passes increases with a decrease in stir zone (SZ) grain size. Consequently, it was found that applying FSP passes continuously enhances the materials' microhardness and tensile characteristics. In the microstructure development of the stir zone during the ZrO2 nanoparticle FSP, dynamic recrystallization (DRX) was an essential mechanism. The main reason for this is that surface nanocomposites with homogenous ZrO2 particle dispersion and no discernible particle clustering in the stir zone were shown by microstructural studies conducted through FSP, which significantly reduced the matrix grain size. The AA1050 base metal (BM) has an ultimate tensile strength, yield strength, and hardness of 59.2 MPa, 24 MPa, and 30.1 respectively. The nanocomposite generated by 5 FSP passes exhibits improved yield stress (55 MPa), tensile strength (94.5 MPa), and microhardness (86.5 HV), but its tensile ductility decreased from 34% to 23.8% when compared to the base metal. Tensile strength that is higher is the outcome of fine dimples' ability to pin the dislocation movement during tensile loading. According to fractographic studies, the ductile–brittle mode replaced the dimple-shaped ductile fracture mode.