Interface Migration And Mechanical Property Of Aluminum Friction Stir Spot Welding Joints

Friction stir spot welding of2mm thick sheets of A6061aluminum alloy wasconducted using tool with cylindrical pin. Influence of pin shape and welding processparameters on interface migration and properties of the joints were investigated. Plasticmaterial flow in the plate thickness direction was observed using lap joint of differentaluminum alloy. The process of interface migration of the lap joint was investigated byplastic material flow.The results showed that when using the pin with left thread, interface migratedupwards, which was affected by the ring plastic material flow in the plate thickness. Thearea above the tip of the migrated interface was metallurgical bonding. When using thepin with right thread, interface migrated downwards, which was affected by the ringplastic material flow in the plate thickness. The area below the tip of migrated interfacewas metallurgical bonding. When using the smooth pin, there was not obvious interfacemigration. The area near to the key hole was metallurgical bonding. The tensile shearload was the biggest when using the pin with left thread.When pin length increased, the tensile shear load increased as the effective spotwelding width and the quantity of embedded metal increased using the pin with leftthread. Influence of plunge speed of pin on interface was not obvious. The effective spotwelding width increased and the effective sheet thickness decreased as increased thedepth of shoulder and rotational speed. The effective spot welding width decreased andthe effective sheet thickness increased as increased the plunge speed of shoulder.Compared to the plunge speed of pin, the influence of plunge depth of shoulder oninterface migration was obvious. When the plunge depth of shoulder was0.5mm,rotational speed was1550r/min, plunge speed of pin was60mm/min and plunge speedof shoulder was6mm/min, the effective spot welding width and effective sheetthickness were big (1.76mm and1.16mm). The tensile shear load of the joint was thebiggest, about5366N. It was equivalent to the riveting joint which the diameter of therivet was4.5mm and bigger than the resistance welding joint which the diameter of thenugget was about6.35mm. There were two kinds of fracture model,â… fracture wasshear fracture, â…¡fracture was the mixture fracture of tensile and shear. The tensileshear load was bigger when the joint occurred mixture fracture than when the jointoccurredâ… fracture.