Effect of ex situ Al₃Zr intermetallic on cold and hot wear behaviors and mechanical properties of FSPed surface hybrid nanocomposite of high-strength aluminum matrix

The extraordinary mechanical properties of AA7075-T6 alloy are comparable to that of steel, but its low hardness, high wear rate at room and high temperature have limited its widespread use, so the main aim of this study is to eliminate these weaknesses by producing a hybrid surface composite with the help of an intermetallic compound (Al₃Zr) and other reinforcements (Al₂O₃ and ZrO₂). Friction stir processing was chosen for this purpose, so in addition to obtaining extremely refined grains, the formation of common defects, occurring in the conventional methods, could be avoided. Having produced the composite, surface appearance was evaluated and microstructural characteristics were investigated by stereo, light, and FESEM microscopes. Besides not observing any external and internal critical defect, ultra-fine grains were seen. For a detailed investigation, EDS and XRD analyses were used. To assess mechanical properties, tensile and microhardness tests were conducted. Although yield and UTS experienced a fall, the particles set the stage for remarkable improvements in microhardness, cold, and hot wear. Microhardness was raised uniformly in the whole stir zone, and a ~ 48% rise in this property was obtained. Moreover, hot and cold wear resistances were improved up to about 85% and 65%, respectively. Finally, to study the mechanisms of the fracture and wear, the surfaces were scrutinized under SEM and EDS. It was observed that the fracture had a combination of ductile and brittle behaviors and in worn surfaces, instead of cavities formation, micro-cracks and scratches were produced, which are the signs of enhancement in wear resistance.