薄壁TA2钛管高频焊接接头的组织和力学性能

Microstructure and mechanical properties of high frequency welded joints of thin-walled TA2 titanium tubes

采用光学显微镜和扫描电镜分析了壁厚为0.5 mm的TA2钛管高频感应焊接接头的组织,并对焊缝和母材进行了力学性能测试。结果表明:当焊接速度为60 m/min,焊接功率为18~21 kW,热输入为18~21 kJ/m,挤压量为0.200 mm时可获得成形性好、无宏观缺陷的焊接接头,焊缝连续笔直,表面无裂纹,外毛刺连续均匀。焊接接头组织在焊后冷却过程中发生了不完全转变,部分α相转变为α′相,焊缝及热影响区的组织由粗大锯齿状α相和部分针状α′(针状马氏体)相组成。焊缝及母材显微硬度呈“M”型对称分布,两侧热影响区硬度最高,母材次之,焊缝中心硬度最低。焊接热影响区针状马氏体的存在是导致硬度显著高于母材的主要原因。在合适的工艺条件下,焊接接头的平均抗拉强度为446.8 MPa,达到母材的82%;伸长率为16%,低于母材(26%),焊接接头断口有明显的韧性断裂特征。

Microstructure of high frequency induction welded joint of TA2 titanium pipe with wall thickness of 0.5 mm was analyzed by optical microscope and scanning electron microscopy, and mechanical properties of weld and base metal were tested. The results show that when the welding speed is 60 m/min, the welding power is 18-21 kW, the heat input is 18-21 kJ/m and the extrusion amount is 0.200 mm, the welded joint with good formability and no macro defects can be obtained. The weld is continuous and straight, the surface is free of cracks and the external burr is continuous and uniform. The microstructure of the welded joint changes incompletely in the process of post weld cooling, which is partial α phase transformation to α′ phase. The microstructure of weld and heat affected zone is composed of coarse serrated α phase and partial acicular α′(acicular martensite) phase. The microhardness of weld and base metal is distributed symmetrically in “M” shape, the microhardness of heat affected zone on both sides is the highest, the base metal is the second, and the hardness of weld center is the lowest. The existence of acicular martensite in welding heat affected zone is the main reason why the hardness is significantly higher than that of base metal. Under appropriate process conditions, the average tensile strength of the welded joint is 446.8 MPa, reaching 82% of the base metal, the elongation is 16%, which is lower than that of the base metal(26%), and the fracture of the welded joint has obvious ductile fracture characteristics.