Evolutions of material flow and intermetallic compounds, and the correlations with mechanical properties of dissimilar Al/Cu friction stir welding joints

In the present paper, the evolutions of material flow and intermetallic compounds (IMCs) during friction stir welding (FSW) of dissimilar Al/Cu with two different plate positions are analyzed to elucidate the correlations with mechanical properties of the joints. Under the tool rotation speed of 700 rpm and the welding speed of 110 mm/min, the Al or Cu plate is located at the advancing side (AS) and the retreating side (RS), which are marked as Al-AS/Cu-RS and Al-RS/Cu-AS, respectively. The results demonstrate that material flow plays a significant role on both the formation and the distribution features of IMCs during FSW with different plate positions. For Al-AS/Cu-RS, the dissimilar material was deposited immediately behind the tool without being drawn into the pin rotating, so that a regular two-layer IMCs within a thickness of 1.5 mu m are formed throughout the Al/Cu bonding interface. For Al-RS/Cu-AS, the dissimilar material is sticking with the tool and rotating for multiple circles before it is finally deposited, both two-layer and three-layer IMCs are observed with the thickness ranging from 0.5 to 4.0 mu m at the Al/Cu bonding interface, and a multitude of IMCs are also formed in the intermixing zone, which are both confirmed to be detrimental to the joint mechanical performance. Therefore, the ultimate tensile strength of the Al/Cu joint improves by over 20% with changing the position of Cu plate from the AS to the RS in FSW.