Friction stir lap welding thin aluminum alloy sheets

In this work, thin aluminum alloy sheets with thickness of 0.8 mm were friction stir lap welded using small shoulder plunge depths of 0 and 0.1 mm. The joint formation, microstructure and mechanical properties were investigated. Results show that voids appear inside the stir zone when the small plunge depth of 0 mm is used because the tool shoulder cannot exert a good material-collecting effect at such low plunge depth. A plunge depth of 0.1 mm causes tight contact between the shoulder and the material and thus results in good material-collecting effect, which is helpful to eliminate the void. Sound joints are attained at a wide range of welding parameters when using the shoulder plunge depth of 0.1 mm. No crack is observed inside the bonding ligament. The joints own higher failure loads when the retreating side (RS) of the joint bares the main load during the lap shear tests. The shear failure load first increases and then decreases with increasing the rotating and welding speeds, and the maximum failure load of 6419 N is obtained at 600 rpm and 150 mm/min. The hardness of the joint presents a "W" morphology and the minimum hardness is obtained at the heat affected zone. The joints present tensile fracture and shear fracture when the advancing side and RS bare the main loads, respectively.