基于正交试验的TC4钛合金激光焊工艺优化研究

目的 探究激光功率、焊接速度、离焦量对TC4钛合金激光焊接接头宏观形貌、微观组织及力学性能的影响。方法 通过正交试验方法，研究激光功率、焊接速度、离焦量对接头拉伸性能的影响，并将这3个工艺参数转换为热输入，进一步研究热输入对接头形貌、组织及力学性能的影响。结果 当热输入低于95 J/mm时，焊接接头上下熔宽比较大，焊缝截面呈“V”形;当热输入高于250 J/mm时，接头组织晶粒粗大，甚至出现气孔、错边等冶金缺陷;当热输入为125 J/mm时，焊缝成形美观，焊接接头上下熔宽比接近1，焊缝截面呈“H”形。焊缝区组织主要由原始α相、β相及冷却阶段生成的αʹ相组成，随着热输入的增大，β相柱状晶尺寸逐渐粗化，αʹ针状马氏体相尺寸也相应增大。此外，焊接速度和离焦量对拉伸性能有显著影响，拉伸性能随着热输入的增大呈现先升高后降低的趋势，断口呈韧性断裂特征。当热输入为125 J/mm时，拉伸性能达到最佳，断裂位置发生在母材区，抗拉强度为1 010 MPa，断后延伸率为9.82%;焊缝区中心区域显微硬度高于热影响区及母材区显微硬度。结论 当热输入为125 J/mm时，在TC4钛合金激光焊下，可获得成形美观、性能优良的焊接接头。

Optimization of TC4 Titanium Alloy Laser Welding Process Based on Orthogonal Experiment

The work aims to discover the effects of laser power, welding speed and defocusing amount on the macro morphology, microstructure and mechanical properties of the TC4 titanium alloy laser welded joint. The effects of laser power, welding speed and defocusing amount on the tensile properties of the joint were studied by orthogonal test method and the relevant welding process parameters were converted into heat input to further investigate the effects of heat input on the morphology, microstructure and mechanical properties of the joint. When the heat input was lower than 95 J/mm, the upper and lower melting width ratio of the welded joint was large, presenting a “V” type. However, when the heat input increased to 250 J/mm, coarsening phenomenon occurred in the internal microstructure of the joint, and even metallurgical defects such as pores and misalignment were found. When the heat input was 125 J/mm, the macroscopic formation of the joint was beautiful, and the upper and lower melting width ratio of the welded joint was close to 1, presenting an “H” type. Besides, the microstructure of the weld zone was mainly composed of the original α phase, β phase and αʹ phase generated in the cooling stage. With the increase of heat input, the β phase columnar crystal size gradually coarsened, and the αʹ acicular martensite phase size increased correspondingly. In addition, the welding speed and defocusing amount had a more significant effect on the tensile properties compared with laser power, and the tensile properties firstly increased and then decreased with the increase of heat input. When the heat input was 125 J/mm, the tensile fracture was located in the base metal zone, the tensile strength was 1 010 MPa, and the elongation after fracture was 9.82%, which indicated an optimized tensile property. The microhardness in weld zone was higher than that in heat affected zone and base metal zone. When the heat input is 125 J/mm, the TC4 titanium alloy welded joint with beautiful shape and excellent properties can be obtained by laser welding.