12 mm厚TC4钛合金激光-MIG复合焊接头组织与性能研究

目的 探究TC4激光-MIG复合焊接头显微组织与基本力学性能之间的联系，分析接头不同区域的断裂行为。方法 利用激光-MIG复合焊制备TC4钛合金对接接头，采用光学显微镜和扫描电镜观察接头焊缝区、热影响区及母材的显微组织，在室温下进行了显微硬度测试、拉伸性能测试与断裂韧性测试，并对试样断口进行了观察分析。结果 接头的焊缝区组织为粗大的β相柱状晶，晶内纵横分布着αʹ针状马氏体和针状α相，靠近焊缝一侧的热影响区则由针状αʹ相、α集束与少量细小的块状α相构成。随着远离焊缝中心，母材侧热影响区组织转变为块状的α相、少量α集束及初生β相，并最终趋于与母材组织相似。热影响区的显微硬度值达到最大，这是因为该区域存在比焊缝区更为细小的针状αʹ相。接头的平均抗拉强度和断后伸长率分别为1 020.22 MPa和7.38%。接头在拉伸时主要在焊缝区发生断裂。焊缝区展现出比母材区和热影响区更优异的断裂韧性，平均值为87.14 MPa.m^1/2，焊缝区内纵横交错的网篮组织与集束是其断裂韧性较高的主要原因。结论 在TC4钛合金的激光-MIG复合焊过程中，针状α相和αʹ马氏体的存在会提高焊缝的显微硬度和断裂韧性，但相较于母材塑性没有提升，通过调控焊缝区显微组织结构，可以获得所需性能的接头。

Microstructure and Mechanical Properties of 12 mm Thick TC4 Titanium Alloy Laser-MIG Hybrid Welded Joints

The work aims to investigate the relationship between microstructure and fundamental mechanical properties of TC4 laser-MIG hybrid welded joints, and to analyze the fracture behavior of different regions of the joints. The TC4 titanium alloy butt joints were obtained by laser-MIG hybrid welding and the microstructures of weld metal (WM), heat-affected zone (HAZ) and base material (BM) were observed by optical microscope and scanning electron microscope. Microhardness test, tensile property test and fracture toughness test were conducted at room temperature, followed by observation and analysis of specimen fractures. The microstructure of WM was composed of coarse β-phase columnar crystals, with α''-acicular martensite and acicular α-phase distributed longitudinally and transversely within the crystals. HAZ near WM side consisted of acicular αʹ phases, α colonies and a few fine massive α phases. As moving away from the center of weld, the microstructure of HAZ near BM side transformed into a massive α-phase, a few α-collections and incipient β-phase, and eventually tended to be similar to that of BM. The microhardness values in HAZ reached a maximum, which was attributed to the presence of finer acicular αʹ phase compared to BM. The average tensile strength and post-rupture elongation ratio of the joints were 1 020.22 MPa and 7.38%, respectively. During tensile test, the joint primarily fractured in WM. The WM exhibited better fracture toughness properties than BM and HAZ, with an average value of 87.14 MPa.m1/2. The intersecting basket-weave microstructure and colonies within WM were the primary reasons for its higher fracture toughness. In the process of laser-MIG hybrid welding of TC4 titanium alloy, the presence of acicular α-phase and α''martensite increases the microhardness and fracture toughness of the weld, but the plasticity is not elevated in comparison with that of the base metal. Hence, a joint with the desired properties can be obtained by modulating the microstructure of the weld zone.