热输入对5A06-6061铝合金搅拌摩擦焊接头断裂特征的影响

To investigate the influence of heat input on the fracture behavior of the joints, the 5A06-H112 and 6061-T651 aluminum alloys were friction stir welded in both nature cooling and forced air cooling. When the ratio of rotational speed to transverse speed is 1.5 r/mm, the materials in the nugget zone were insufficiently mixed to form a kissing bond, resulting in brittle fracture along this defect. As the ratio reaches 3.0 r/mm, the materials in the nugget zone were well mixed, and ductile fracture occurs in the heat affected zone of 6061 aluminum alloy. With the increase of heat input, the fracture angle gradually decreases from 41° to 3°, and the fracture mechanism changes from shear fracture to normal fracture. The distribution of nanoindentation hardness of the FSW joints indicates that the heat affected zone of 6061 aluminum alloy is the weakest area, and the fracture angle of the joint is directly influenced by the width and angle of this weakened area. SEM images of the fracture surface reveal that supressing the heat input could increase the fracture angle and cause shear fracture, which is conducive to form more shear dimples on the fracture surfaces to improve the elongation of the joints.