Characterization of AA7075 Surface Composites with Ex Situ Al2O3/SiC Reinforcements Tailored Using Friction Stir Processing

Automotive monocoque is in need of AA7075 with enhanced strength and hardness properties. Fabrication of Surface Hybrid Composites (SHCs) by Friction Stir Processing is a prominent technique to satisfactorily enhance the aforementioned characteristics. SHCs are formed through different volume proportions of Al2O3/SiC reinforcements. Heat generation during the processing stage shows a linear trend along the longitudinal axis due to the thermal conductivity of AA7075. Microstructure of composites is observed with fine grain formation and homogeneous distribution of reinforcements. X-ray Diffraction pattern confirms the existence of both reinforcements in matrix alloy. Specimens with identical volume ratio of Al2O3 and SiC particles depict the superior micro-hardness of 265 VHN which is 8.5 and 19.08% higher than the individual contribution of reinforcements. This is attributed to the homogeneous settlement of reinforcements and particle pinning with parent matrix. Addition of Al2O3 improves the impact toughness due to its wettability with base AA7075 as a result of Al-Al bond. Incorporation of SiC particles enhances the Ultimate Tensile Strength of the composites by virtue of its high load-bearing capacity. Fracto-graphic analysis of the specimens with different Al2O3/SiC weight ratios indicated the fractures along the breakdown of reinforcement particles.