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In this paper, 7050-T6 high-strength aluminum alloy with 3-mm-thickness is taken as the research object, and it is welded by CMT Advanced 4000R NC welding system. The microstructure, mechanical properties, evolution of joint phase and fatigue properties are studied, and the tensile and fatigue fracture are observed and analyzed. It is found that the fusion zone is dominated by columnar crystal structure and typical epitaxial solidification; the structure of weld zone is mainly equiaxed crystal and dendrite. After 360 h of natural aging, the hardness distribution of the joint is not uniform, and the hardness of the weld zone is the smallest. The hardness of the overaging softening zone is 10 HV lower than that of the solid solution zone, and a softening zone with a width of about 5 mm appears in the joint. The HAZ softens obviously, and the fracture surface shows typical dimple fracture morphology. The results show that the conditional fatigue limits of the specimens are 166.4 and 109.3 MPa respectively under the condition of setting Nf = 107 fatigue cycle. The fatigue initiation area of the joint is mainly welding porosity, and the fatigue striation spacing of the extension area is different. In the process of crack propagation, the striation tends to bypass the second phase particles; The instantaneous fracture area consists of dimples of different sizes. The thermal simulation test of the weld is carried out through the moving Gaussian heat source model in ANSYS software. In addition to the plate-like Mg2Si phase observed in the weld, FeAl3 and (FeMn)Al6 impurity phases are also found, only a weak diffraction peak of MgZn2 phase is found in the solid solution zone. The microstructure evolution of HAZ is analyzed by HRTEM images. It is found that there are tiny GP zone precipitates in the solution zone. [ABSTRACT FROM AUTHOR]

In this study, using synchrotron radiation X-ray imaging, the microstructure, tensile properties, and fatigue properties of FGH96 nickel-based superalloy were tested, and the fatigue damage mechanism was analyzed. An analysis of the experimental results shows that the alloy structure is dense without voids or other defects. It was observed that the primary γ′ phase is distributed on the grain boundary in a chain shape, and the secondary γ′ phase is found inside the crystal grains. The X-ray diffraction (XRD) pattern indicates that no other phases were seen except for the γ and γ′ phases. The tensile strength of the alloy is 1570 MPa and the elongation is 12.1%. Using data fitting and calculation, it was found that the fatigue strength of the alloy under the condition of 5 × 106 cycles is 620.33 MPa. A fatigue fracture has the characteristics of secondary crack, cleavage step, fatigue stripe, tire indentation, and dimple. The fracture is a mix of cleavage fracture and ductile fracture. Through a three-dimensional reconstruction of the alloy synchrotron radiation imaging area, it was found that the internal defects are small and mostly distributed at the edge of the sample. The dimple morphology is formed by cavity aggregation and cavity germination resulting from defects in the material itself, fracture of the second-phase particles, and separation of the second-phase particles from the matrix interface. By analyzing the damage mechanism of fatigue fractures, it is concluded that the cleavage step is formed by the intersection of cleavage planes formed by branch cracks, with the main crack of the confluence extending forward to form a cleavage fracture. The crack propagation path was also analyzed, and under the action of cyclic load and tip passivation, the crack shows Z-shaped propagation. [ABSTRACT FROM AUTHOR]