Multipass Dissimilar Friction Stir Welding of Al Alloys

In this research, effect of second pass of friction stir welding on the microstructure mechanical properties of dissimilar aluminium alloys welds was studied. For this purpose, Al - Si and Al - Mg alloys were used as base metals. Microstructure of base metals and stirred zone of welds were investigated by optical and scanning electron microscopes. Mechanical properties of welds were studied by tensile test and compared with that of the base metals. Based on the results it was observed that by applying the second FSW pass, mixing of the base metals in the stirred zone was changed from mechanical to chemical mixing. Accordingly, the tensile properties of the ۲-pass weld considerably increased compared to the ۱-pass weld so that fracture stress and strain increased from ۶۰.۶ to ۱۱۳.۷ MPa (~۸۸%) and ۲ to ۴ % (۱۰۰%), respectively. It was concluded that by increasing the welding pass from ۱ pass to ۲ passes, the joining mechanism changed from mostly mechanical locking to mainly metallurgical bonding. It was revealed that the second FSW pass is extremely beneficial to the microstructure and mechanical properties and hence weld quality of dissimilar aluminium alloys welds .

Keywords:

Friction Stir Welding , Dissimilar , Multipass , Aluminium Alloys , Microstructure.