Abstract
Laser-MIG hybrid welding of 6061-T6 aluminum alloy was carried out with ER4043 welding wire, and the microstructure and fatigue properties of the joint were studied. The grain size of HAZ is larger than that of base metal (BM) due to the influence of welding heat cycle. Snowflake-like equiaxed grains were found in the upper, middle, and lower parts of the welded joint (WJ). Based on the fatigue test with 1 × 106 cycles, the ultimate fatigue strength of BM and WJ is 101.9 MPa and 54.4 MPa, respectively. There are many pores with different sizes in WJ. The number of pores in the upper and middle parts of WJ is obviously larger than that in the lower part due to the influence of the cooling rate of the weld pool and the escape rate of pores. The porosity type is mainly metallurgical pores with regular morphology, which is mainly due to the bubbles formed by the evaporation of Mg elements and H2O in the oxide film on the BM surface. The fatigue fracture analysis shows that the main cause of fatigue crack is the near-surface pores with 460 μm and 190 μm, respectively. The existence of pores near the surface is equivalent to the formation of a large-scale prefabricated crack, resulting in serious stress concentration. The morphology of the grains around the pores has a great influence on the initiation and propagation of the fatigue microcracks.
Highlights
6061-T6 aluminum alloy is a medium strength heat treatable aluminum alloy with Mg and Si as the main alloying elements
6061-T6 aluminum alloy with thickness of 3 mm, which is widely used in high-speed train body, is selected as base metal (BM), and laser-metal inert gas welding (MIG) hybrid welding process is used for connection. e microstructure and fatigue properties of WJ and BM were analyzed. e purpose of this paper is to evaluate the fatigue properties of 6061 aluminum alloy laser-MIG hybrid welded joint and discuss the fatigue failure of 6061 aluminum alloy laser-MIG hybrid welded joint from the perspective of pores forming, fatigue microcrack initiation, and propagation mechanism near the pores
It can be found that there are many different sizes of pores scattered on WZ, among which the number of pores in the upper and middle of WZ is obviously larger than that of the lower part, while the large size pores are mostly distributed in the middle part
Summary
6061-T6 aluminum alloy is a medium strength heat treatable aluminum alloy with Mg and Si as the main alloying elements. Due to the welding heart cycle, the grain orientation, the second phase particle behavior, and the surrounding internal stress of the traditional fusion welding processes, namely, tungsten inert gas welding (TIG) and metal inert gas welding (MIG), will change significantly Problems such as coarse structure, defects (welding hot cracks and pores), and burning loss of strengthening alloy elements (Mg and Zn) will occur in the welded zone [4,5,6]. Compared with these disadvantages of MIG welding, laser welding has the advantages of high welding efficiency, small heat input, and small deformation [7,8]. Ese studies show that, compared with traditional welding methods (such as MIG), laser arc welding joint of aluminum alloy has smaller residual stress and greater tensile strength
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