Influence of aluminium alloy grade on dissimilar friction stir welding of aluminium to AZ31B

There is increasing research interest in joining lightweight metals, such as aluminium to magnesium, for potential applications in the transportation sector. The friction stir welding (FSW) technique may inhibit grain coarsening and the evolution of intermetallic compounds (IMCs) that evolve when using conventional fusion welding methods to join such dissimilar metals. The current investigation reports on the effect of using two different aluminium alloys on the joint quality in the FSW of Al to Mg grades (AZ31B). Aluminium grades AA5083 and AA6061 were separately welded to AZ31B at different tool rotational speeds (ω) and traverse speeds (v). The optimal process parameters for achieving defect-free joints were identified by examining the joints macro and microstructure, as well as assessing the presence and distribution of IMCs using energy dispersive spectroscopy and X-ray diffraction techniques. Additionally, the hardness distribution of different weld zones allowed for the joint mechanical strength to be predicted. Dissimilar FSW of Al to AZ31B was influenced by the aluminium grade, in that the highest joint mechanical strength was achieved when AZ31B was FSWed to the harder aluminium grade (AA6061). Placing the AZ31B on the advancing side (AS) with no tool offset, 1000 rpm tool rotational speed and 100 mm/min traverse speed, delivered defect-free joints. Additionally, several IMCs such as Al3Mg2 and Al12Mg17 were identified at the weld nugget of the dissimilar joints, the presence of which resulted in higher hardness values at the weld nugget compared to the parent metals