Research on microstructure and properties of TC4 titanium alloy MIG welded joints after heat treatment
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摘要: 对TC4钛合金MIG焊焊接接头进行焊后热处理，采用盲孔法、拉伸、冲击、金相、扫描等方法对接头进行试验与分析，研究不同热处理工艺对残余应力、组织和力学性能的影响。结果表明：焊接接头经焊后热处理，横向残余应力和纵向残余应力平均值最大降为74.2 MPa和70.1 MPa；未热处理接头母材区为α+β片层组织，焊缝区为α'针状马氏体组织，热影响区为α和α'混合组织。热处理后，随着热处理温度和时间的增加，焊缝组织中的针状α'马氏体粗化，晶粒尺寸增加；未热处理接头焊后拉伸断裂位置为母材处，接头强度高于母材。在650 ℃+2 h的热处理工艺下，接头延伸率较未热处理状态提高，断裂方式为韧性断裂，保温时间延长至3 h，晶粒粗大、延伸率降低。接头室温冲击功焊后状态能够达到母材的95%，经焊后热处理后接头得到软化，室温冲击功相比焊后状态有所下降。Abstract: Post heat treatment processes had been carried out on TC4 titanium alloy MIG welded joints. The effects of different heat treatment processes on residual stress, microstructure and mechanical properties on resulting TC4 titanium alloy MIG welded joints had been investigated through the blind-hole method, mechanical test and microstructure observation. The results show that average transverse residual stress and longitudinal residual stress of the welded joint after post heat treatment are reduced down to 74.2 MPa and 70.1 MPa, respectively. The base material is α+β lamellar structure, and the weld joint is α' needle shape martensite structure, the heat-affected zone is a mixed structure of α and α'. After heat treatment, with increasing heat treatment temperature and prolonging time, the acicular α' martensite in the weld structure becomes coarser, and grain size increases. For unheated-treatment joint, tensile fracture position locates at base metal, indicating higher joint strength compared with the base material. When the weld joint is subjected to a heat treatment process of 650 ℃+2 h, the elongation of the joint is higher than that in the unheated state, and the fracture mode is a ductile fracture. When the holding time is extended to 3 h, the grain becomes coarse, and the elongation decreases. The impact energy of the welding joint after post heat treatment at room temperature can reach 95% of that of base metal. The post-weld heat treatment can soften the welding joint, resulting in lower room temperature impact energy than the as-welding joint.
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Key words:
- TC4 titanium alloy /
- MIG welding /
- post-weld heat treatment /
- mechanical properties /
- microstructure
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图 2 不同焊后热处理工艺下残余应力值
Figure 2. Residual stress values of samples under different post-weld heat treatment processes
图 3 TC4钛合金MIG焊焊接接头显微组织
（a）焊接接头；（b）母材区；（c）焊缝区；（d）热影响区
Figure 3. Microstructure of TC4 titanium alloy MIG welded joint
图 4 不同焊后热处理工艺下接头焊缝区的微观组织
Figure 4. The microstructure of the joint weld zone under different post-weld heat treatment processes
图 5 不同热处理工艺下各接头拉伸性能
Figure 5. Tensile properties of individual joint under different heat treatment processes
图 6 MIG焊接头断口形貌
(a)整体；(b)局部；(c)放大；(d)韧窝
Figure 6. Fracture appearance of MIG welded joint
图 7 不同焊后热处理条件下的拉伸断口形貌
Figure 7. Tensile fracture morphology of samples under different post-weld heat treatment conditions
图 8 不同焊后热处理工艺下接头的室温冲击功
Figure 8. Room temperature impact energy of joints under different post-weld heat treatment processes
表 1 TC4钛合金MIG焊焊接工艺参数
Table 1. Welding process parameters of TC4 titanium alloy MIG welding
焊接层次 焊接电流/A 焊接速度/
（m·min−1）弧长修正/% 脉冲修正/% 摆动/
（Hz·mm）干伸长
/mm打底层 150 0.4 30 0 3×1 22 填充层 150 0.25 30 0 3×7 22 
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表 2 真空热处理工艺参数
Table 2. Process parameters of vacuum heat treatment
工艺编号 加热温度T/℃ 保温时间t/h 冷却方式 1# 未热处理 2# 550 3 炉冷 3# 650 2 炉冷 4# 650 3 炉冷
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