Ductility Improvement in Commercially Pure Aluminium by Friction Stir Processing

Abstract

Commercially pure aluminium (cp-Al) is a common structural material whose ductility is not very impressive (percentage elongation at break ~10%). This paper reports friction stir processing (FSP) as a method to improve the ductility of cp-Al without compromising the strength and hardness of the material. Different combinations of process parameters, namely tool rotational speeds in the range of 560–1400 RPM and tool traverse speeds in the range of 100–200 mm/min were explored to identify the influence of those parameters on the mechanical properties of the material. The ultimate tensile strength (UTS) and percentage elongation at break were evaluated by conducting tensile test of transverse specimens, and the microhardness across the processed zones was also measured. Grey relational analysis (GRA) was carried out to find out the optimum parameter combination using which the most suitable combination of strength, ductility and microhardness can be achieved. From this analysis, tool rotational speed of 1400 RPM with the tool traverse speed of 160 mm/min was identified as the optimized processing condition that can result in up to 83.9% improvement in percentage elongation at break with 26.52% improvement in the UTS and 7.27% improvement in the microhardness as compared to cp-Al. Finally, a quadratic regression model was developed to establish a relationship between ductility and the input parameters, i.e., rotational speed and traverse speed.