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Metals 2016, 6(4), 87; doi:10.3390/met6040087
Abstract: Friction stir lap welding of 7B04 aluminum alloy was conducted in the present paper, and the effect of welding speed on the defect features and mechanical performance of lap joints was investigated. The results indicate that the hook defect at the advancing side (AS) can reduce the effective thickness of the top sheet, and the sheet thinning level is gradually lowered by increasing the welding speed. The cold lap defect at the retreating side (RS) can result in effective thickness reduction in both top and bottom sheets, and the total height of the cold lap defect varies slightly with the welding speed. The tensile properties of the lap joints are largely related to the sheet thinning levels caused by the defects. The fracture strength of AS-loaded lap joints is progressively increased with increasing welding speed, while that of RS-loaded lap joints evolves slightly with welding speed. It is found that the affecting characteristic of loading configuration on the joint performance is also dependent on the welding speed. At lower welding speeds, the AS-loaded lap joints show lower fracture strength than the RS-loaded lap joints. When the welding speed is high, the AS-loaded lap joints present superior tensile properties to RS-loaded lap joints.
2. Materials and Methods
3.1. Defect Features of Lap Joints
3.2. Mechancial Performance of Lap Joints
4.1. Evolution of Tensile Properties with Welding Speed
4.2. Effect of Loading Configuration on Joint Properties
- The increase of welding speed can remarkably limit the upward motion of the initial faying surface, which lowers the level of top sheet thinning induced by the hook defect. The cold lap defect can result in the reduction of effective thickness in both the top and bottom sheets. The height of the cold lap defect is decreased in the top sheet but gradually increased in the bottom sheet when the welding speed is increased, leading to a slight variation in the total height of the cold lap defect with the welding speed.
- The tensile properties of FSLW joints are largely related to the level of sheet thinning caused by the hook and cold lap defects. In the AS loading configuration, the fracture strength of AS-loaded lap joints is significantly increased with increasing welding speed, while for the RS loading configuration, the fracture strength of RS-loaded lap joints varies slightly with the welding speed. Local bending and rotating occurred in the lap joints during the tensile test. The rotating angle of the lap sheets and the fracture strength of the lap joints exhibit similar evolving trends with the welding speed in both AS and RS loading configurations.
- The affecting characteristic of loading configuration on joint performance is dependent on the welding speed. At lower welding speeds, the AS-loaded lap joints show lower fracture strength than the RS-loaded lap joints. When the welding speed is high, the AS-loaded lap joints then present larger tensile properties than RS-loaded lap joints. In order to obtain the high performance of lap joints, a relatively high welding speed should be applied during FSLW. Meanwhile, the loading side of the joint, AS or RS, should possess a larger effective thickness in the joint.
Conflicts of Interest
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|Chemical Compositions (wt. %)||Mechanical Properties|
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