Research on the Effect of the Processing Parameters on Susceptibility of Liquation Cracking of Al Alloys During Refilled Friction Stir Spot Welding

摘要

Refilled friction stir spot welding (FSSW) has a great potential to be a versatile process for mass producing high strength Al alloys. But, the liquation cracking susceptibility of refilled FSSW welds is high, which greatly deteriorate the mechanical properties. In this paper, the microstructure of the liquation cracking was observed and the cracking mechanism was analyzed. The results showed that, a lot of hole-type-cracks were found distributing continuously, as a chain, along the grain boundaries, and there are many melted intermetallic compounds around the holes. With EDS analysis, the mechanism of liquation cracking during refilled FSSW was proposed: when the eutectic temperature reached, constitutional liquation was initiated by the eutectic reaction between intermetallic compounds and the α-Al matrix. So that the bonding between grains was weakened and the cracking along the grain boundaries could be caused by the tension induced by the rotation of the pin and sleeve.