Experimental Investigation on Hybrid Friction Stir Processing using compressed air in Aluminum 7075 alloy

Abstract

Aluminum 7075 alloy is a popular candidate material in aerospace industries due to its excellent strength to weight ratio among the aluminum alloys. Friction stir processing (FSP) is a solid state process to refine the microstructure that results into enhanced mechanical properties such as hardness and superplasticity. FSP of 7075Al has proven to obtain superplasticity, which eliminated need of joint in structural applications. The thermal history during the process greatly affects the resulting microstructure. By reducing the process temperature, the grain growth of 7075Al gets inhibited and hence very fine grain microstructure can be produced, which is a primary requirement for obtaining superplasticity. Even though FSP maintains the process temperature below the melting point, the approach of hybrid FSP with active cooling offers further reduction in the generation of process temperature. Hybrid FSP with active cooling is one of the variant of FSP. In this study, 7075Al was subjected to normal FSP and hybrid FSP with compressed air cooling (shown in graphical abstract) under constant process parameters. Active cooling FSP sample reported considerable reduction in the temperature in comparison to normal FSP. No surface defect was observed in the processed zone for both the samples. The optical micrograph revealed fine equiaxed grain structure in the stir zone for both the samples. Hybrid FSP samples reported elongated fine grain microstructure in comparison to the normal FSP due to less heat input during the process.