Friction Stir Surface Processing of Al 6061 Alloy: Role of Surface Alloying with Copper and Heat-Treatment

Abstract

The current paper focuses on enhancing the surface hardness of the heat-treatable Al-alloy using the combined approach of thermal-spray, friction stir surface processing (FSSP) and heat-treatment. Copper powder was thermal-sprayed in the surface groove of Al 6061 alloy specimens followed by FSSP. Defect-free stirred zone was observed at lower transverse speed of 10 mm/min. The width of the hardness profiles across the stirred zone was increased with increase in the rotational speed of the tool. Grain refining was observed in the stirred zone due to the FSSP. In post-FSSP T6 heat-treatment, aging kinetics in the non-surface-alloyed specimen was accelerated due to the FSSP. Precipitation of Al2Cu phase was observed in the stirred zone. Copper-alloying and post-FSSP heat-treatment were effective in enhancing the surface hardness (about 39% improvement in the surface hardness was observed). © 2018, The Indian Institute of Metals - IIM.