A Materials and Mechanical Characterization of Friction Stir Welded Aluminum-Steel Joints with Respect to Intermetallic Compounds Content

Abstract

In order to weld dissimilar materials with dramatically different properties such as aluminum and steel, friction stir welding (FSW) offers many advantages over conventional fusion welding techniques. However, producing strong and durable FSW joints requires full characterization of these joints including metallurgical and mechanical characterization. In this work, many process parameters and two different tools are put to test and the resulting FSW joints are characterized. Their mechanical strength is investigated in tension with respect to intermetallic compounds content analyzed using SEM coupled to EDX. The soundest 2mm thick joints recovered 55% of the strength of the original un-welded metal whereas in the case of the 3mm thick joints 47% of the strength could only be recovered in the best case. It was revealed that as the content in intermetallic compound increases the strength of the joints decreases. Additionally, it was found that the higher the mechanical deformation, the more these compounds are abundant; in other words, intermetallic compounds were largely found in the middle and bottom sections of the 3mm thick samples which is where the threads of the pin do most of their work. The compositions of these intermetallic phases along the abutting surfaces is also proposed based on the elemental composition of Fe and Al as detected by the scanning electron microscopy.