Abstract
In this paper, the microstructure analysis and performance research of dual laser beam welded 2060-T8/2099-T83 aluminum–lithium alloys were carried out. First, the macroscopic morphology and microstructure characteristics of T-joint aluminum–lithium alloys under different welding conditions were observed. Then the effect of welding parameters and pore defects on tensile and fatigue properties of the weld were carried out and the experimental results were analyzed. It was found that the weld heat input has a significant influence on the penetration of the welded aluminum–lithium alloys joint. When the laser power is too high, the weld will absorb more laser energy and the increase in the evaporation of magnesium will further increase the weld penetration. When the penetration depth increases, the transverse tensile strength tends to decrease. There is no obvious rule for the effect of pore defects on the tensile strength of the weld. At the same time, the heat input of the weld is inversely proportional to the porosity. When the weld heat input increases from 19.41 to 23.33 kJ/m, the porosity decreases from 5.35% to 2.08%. During the fatigue test, it was confirmed that the existence of pore defects would reduce the fatigue life of the weld. In addition, from the analysis of the fatigue fracture morphology it can be found that when the porosity is low, the weld toe is the main source of fatigue cracks. The crack propagation zone shows a typical beach pattern and the final fracture of the base metal presents the characteristics of a brittle fracture. While, when the porosity is high, the crack source is mainly located at the pore defects. T-joint fractures from the inside of the weld and the fracture in the final fracture zone have obvious pore defects and dimples.
Highlights
An aircraft’s structure is composed of tens of thousands of parts
Research on laser beam welding aluminum–lithium alloys has mainly focused on weld formation, microstructure, mechanical properties, porosity and crack sensitivity [13]
This article will take this as a starting point to study the microstructure, Coatings 2021, 11, 693 tensile properties and fatigue performance of laser beam welding aluminum–lithium alloys systematically, and focus the research on the relationship between the tensile and fatigue properties of aluminum–lithium alloys welded joints and their structure and defects
Summary
An aircraft’s structure is composed of tens of thousands of parts. In the early days, the main material used for aircraft manufacturing was aluminum alloy and the connection method was riveting. Research on laser beam welding aluminum–lithium alloys has mainly focused on weld formation, microstructure, mechanical properties, porosity and crack sensitivity [13]. Zhang et al [15] used scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy to characterize the laser-arc hybrid welded AA6082 aluminum alloy’s microstructure and fatigue fracture They discussed the influence of microstructure on different fatigue processes theoretically and found that the microstructure mainly affects the first stage of fatigue crack growth. The reason for this can be attributed to the number of magnesium and zinc precipitations in the weld zone, which change the dislocation movement thereby effectively changing the fatigue crack growth These studies were mainly focused on aluminum alloy and steel. This article will take this as a starting point to study the microstructure, Coatings 2021, 11, 693 tensile properties and fatigue performance of laser beam welding aluminum–lithium alloys systematically, and focus the research on the relationship between the tensile and fatigue properties of aluminum–lithium alloys welded joints and their structure and defects
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