Dissimilar metal welding on Mg AZ31 and AA 6061 alloys by using friction stir welding

The objective of this study is to investigate the mechanical properties and microstructures on dissimilar metal friction stir welding (FSW) between AA 6061 and Mg AZ31 alloys. For the purpose of improving the strength of the dissimilar welded joint, the process parameters such as rotational speeds and travel speeds play a vital role to obtain the better welded joint for dissimilar metals. FSW was performed at travel speeds ranging from 20 to 80 mm/min, with tool rotational speeds ranging from 500 to 1000 rpm. In the experimental work, investigation has been performed using microhardness testing, tensile testing and optical microscopy. This research reveals that using FSW, a welded joint between dissimilar metal alloys AA 6061 and Mg AZ31 can be created by choosing the right tool pin profile and process parameters that are responsible for creating complex recrystallization, grain refining occurred in the stir field. The weld sample rotation speed of 560 r/min and a travel speed of 20 mm/min shows the most contributing parameters of the experiment. The welded specimen had a tensile strength of about 74.4% of that of AA 6061 alloy and 59.3% of that of Mg AZ31 alloy, and it failed through the brittle-mode fracture. The stir zone has a maximum hardness of HV 108 was measured with sample 560, and in the away stir zone, an irregular hardness distribution was obtained with a 50 HV. Due to the high strain rate, the welding tool pin imparts to the material and the heat produced by friction between the material and the tool, dynamic recrystallization (DRX) happens in the stir zone (SZ) of the FSW process.