Experimental investigation of defect formation, microstructure and mechanical properties in friction stir welding of AA5086

Abstract

The joint conditions of a weldment entirely rely on the set of process parameters applied during the welding operation. In friction stir welding (FSW), proper mechanical mixing of the material signifies the appropriate welding variables. The present work aspires to investigate the influence of tool rotational speed (RS), welding speed (WS) and plunge depth (PD) on external as well as internal defect formation, identify the different types of defect encountered during the FSW process, and evaluate the influence of different parameters on tensile properties and microstructure of the joints. In order to achieve the goal of the present work, a detailed experimental investigation was carried out using AA5086-O as base metal. On account of high strength-to-weight ratio, good weldability and high corrosion resistance, friction stir welded joints of aluminum alloys are widely applications in aerospace, automotive, railway and shipbuilding industry. It has been observed that theultimate tensile strength (UTS) of joint tends to decrease when there is increased in the welding speed at constant PD of 0.2 mm and RS of 1400 rpm. Similarly, with consistent PD of 0.3 mm and rotational speed of 2000 rpm, UTS of joints initially enhanced with an increment in welding speed and then reduced eventually. A joint fabricated with maximum rotation speed, intermediate welding speed and the higher plunge depth produced highest tensile strength of 215 MPa which is 16% higher than the conditions required for aerospace applications of FSW for aluminum alloys, as per the standard of American Welding Society (AWS). Microscopic analysis was conducted to scientifically ascertain the grain size, crystal structure and surface morphology of the FSW joints.