Evaluation of the microstructure and mechanical properties of friction stir-welded copper/brass dissimilar joints

Abstract

The present study investigated the effect of the welding heat input on friction stir-welded copper/brass dissimilar joints with an overlap design. For this purpose, the friction stir welding (FSW) process and the rotational non-consumable of H13 hot work tool steel were used. For the overlap joint, the copper was selected as advancing side and the brass was used as retreating side. In order to study the microstructure and fracture surface of the welded samples, an optical microscope and a scanning electron microscope (SEM) were used. In addition, the mechanical behavior of the joint was tested through tensile-shear and microhardness tests. It was found that the copper and brass are formed as layered onion rings in the weld nugget zone (WNZ), and they gradually complete with an increased welding heat input. Maximum microhardness was observed in the WNZ in all the samples. Due to onion ring structure, the microhardness was observed as an M-shaped form in this zone, and the greatest microhardness was related to brass and the smallest microhardness was related to copper. The mechanical properties including tensile-shear strength and microhardness were increased by decreasing the welding heat input. Hence, the maximum tensile strength and microhardness were observed in Sample 450 rpm-16 mm min−1. The fractography of the fracture surfaces of the samples showed that ductile failure occurred in all the samples and fracture type tended to brittle fracture for bigger welding heat inputs. Finally, the best mechanical and microstructural results were observed in Sample 450 rpm-16 mm min−1 due to smaller welding heat inputs as compared to the other two samples.