Study On The Crack Growth Behavior Of Friction Stir Welding With High/Low Profile

Friction stir welding is subjected to complex physical and chemical effects during the welding process,and the mechanical properties of the weld are changed.The mechanical properties of the base metal weld are uneven,that is,the mismatch effect of the weld.The mechanical mismatch makes the weld zone have a different crack growth behavior from that of homogeneous materials,which affects the propagation speed and path of cracks in the weld zone.Therefore,studying the fatigue crack growth behavior in different areas of welded joints is of great significance to the structure design and safety life assessment of friction stir welded joints.In this paper,the microstructure test and tensile test of 5083 aluminum alloy double-shaft friction stir welding were carried out,and compared with the high profile 2A12-O aluminum alloy friction stir welding.The results show that the tensile strength of the weld nugget zone can reach 95%of the base metal,while the tensile strength of the heat-affected zone is 73%of the base metal.The elongation of the weld nugget is 97%of the base metal,and the elongation of the heat-affected zone is only 47%of the base metal.The mechanical properties of 5083 aluminum alloy decrease after welding,and it is a low profile joint.The mismatch ratio M is 0.94.After friction stir welding of 2A12-O aluminum alloy,the performance of the weld is significantly increased compared to BM,which is called high match,and the mismatch ratio M is 1.1.Through the fatigue crack growth rate test of 5083 friction stir welded joints with notches located in different positions,combined with the crack growth behavior of high-match joints,the fatigue fracture mechanism of mismatched joints is analyzed,and its life is predicted.The results show that for the specimens with pre-cracked vertical welds,the growth rate of the low-profile joints is significantly increased when the crack propagates from the base metal area to the weld nugget,while the high-profile joints have a significant effect on cracking and the crack growth rate is significantly reduced.For the samples with pre-crack in the heat-affected zone,the crack growth rates of the two mismatched samples are faster.For the specimens with pre-cracked weld nuggets,the high configuration showed a lower crack growth rate,while the growth rate of the low configuration joint weld nugget was between the other two samples.