Metallurgical Characterization and Hardness Evaluation of Dissimilar Friction Stir Welded Al Alloy Flat Plates

Abstract

Friction Stir Welding (FSW) is commonly developed for welding of metals of the same kind like aluminium copper, steel and titanium. However, FSW also has the potential to produce high-quality joints between dissimilar metals which are differ in physical and mechanical properties. In this work dissimilar aluminium alloys plates of AA 6101-T6 and AA 6351-T6 with 6 mm thick were friction stir butt welded under the influence of different process parameters. The influence of various parameters, particularly the rotational speed on microstructures and hardness properties of the joints has been addressed. The microstructure of weld joints has been studied using an optical microscope and distinct zones are also identified. Fine-equiaxed and refined grains are observed at nugget zone of dissimilar joints due to effective stirring action of cylindrical profile tool pin at higher tool rotational speeds. The intermetallic compounds that form in the joints has been examined by the X-ray diffraction (XRD) and the presence of intermetallic compound Mg2Si in base metals and FSW joints was detected. Therefore, it can be understood that the intermetallic compound affects the hardness of butt joints. The highest and lowest SZ hardness are obtained with the welds fabricated with 1300rpm, 60 m/min, 4kN and with 900 rpm, 60 mm/min and 8kN respectively.