A study on fatigue damage behavior of single-wire MIG welding joint for TC4 titanium alloy
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摘要: 采用单丝MIG焊工艺焊接15 mm厚TC4钛合金，对母材和焊接接头的组织、拉伸性能、疲劳性能进行分析测试。结果表明：焊接接头分为母材、热影响区和焊缝区3个部分，其中母材为α+β等轴组织，热影响区为α+β和α′马氏体组成的混合组织，焊缝区在强烈热冲击作用下，晶粒粗化，晶粒内为α′马氏体组织。接头拉伸试样断裂在母材处，断后延伸率为10.5%。母材和焊接接头疲劳寿命随着应力水平的增加而减小，在高应力水平下，母材疲劳寿命高于母材，低应力水平下则相反；母材疲劳源位于试样表面的划痕处，接头疲劳起源于内部气孔处，接头疲劳扩展区有许多二次裂纹，接头扩展区疲劳条带间距小于母材，接头和母材瞬断区都有大量韧窝。Abstract: A single-wire MIG welding process was carried out to weld TC4 titanium alloy with a thickness of 15 mm. The base metal and welded joint microstructure, tensile, and fatigue properties were analyzed and tested. The results showed that the welded joints were divided into the base metal, heat-affected zone, and weld zone. The base metal had an α+β equiaxed structure, and the heat-affected zone was a mixture of α+β and α′-martensite. The grains in the weld zone presented a coarse state under the intense thermal shock; meanwhile, the α′-martensite structure formed the interior of the grain. The tensile specimen fractured at the base metal, and the elongation after fracture was 10.5%. The fatigue life of base metal and welded joints decreased with increased stress levels. The fatigue life of base metal was higher than that of base metal at high-stress levels but opposite at low-stress levels. The fatigue source of the base metal was located at the surface scratches of the sample, and the joint fatigue originated from the internal pores. Many secondary cracks formed in the fatigue propagation zone of the joint, the spacing of the fatigue bands in the fatigue propagation zone was more minor than that of the base metal, and there were many dimples in the transient fracture zone of the joint and the base metal.
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Key words:
- TC4 titanium alloy /
- single-wire MIG welding /
- microstructure /
- α′-martensite /
- fatigue performance
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图 8 母材和焊接接头疲劳裂纹扩展区形貌
（a）、（b）母材；（c）（d）接头区
Figure 8. Morphology of fatigue crack propagation zone of base metal and welded joint
图 9 母材和焊接接头瞬断区形貌
（a）母材；（b）焊接接头
Figure 9. Morphologies of base metal and transient fracture zone of welded joint
表 1 母材和焊丝化学成分
Table 1. Chemical composition of base metal and welding wire
% Ti Al V Fe C N H O 母材 余量 6.28 4.04 0.136 0.017 0.01 0.001 0.13 焊丝 余量 5.58 4.13 0.22 0.05 0.03 0.015 0.4 
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表 2 焊接工艺参数
Table 2. Welding process parameters
焊接电流/A 焊接速度/(m·min−1) 干伸长/mm 保护气流量/（L·min−1） 弧长修正/% 140～180 0.3～0.6 12～15 20～25 +30
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表 3 拉伸试验结果
Table 3. Tensile test results
样品名称 样品编号 抗拉强度/MPa 延伸率/% 母材 1-1 846 12.5 母材 1-2 840 14.0 母材 1-3 843 11.0 焊缝 1-1 848 11.5 焊缝 1-2 850 11.0 焊缝 1-3 852 12.0
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表 4 疲劳试验测试结果
Table 4. Fatigue test results
样品 应力水平/MPa 疲劳寿命N/次 母材 422 34354900 506 1435500 548 317700 590 118300 焊缝 425 100000000 510 4351100 552 1114700 595 320400
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