Guo Ning, Cheng Qi, Zhang Xin, Fu Yunlong, Huang Lu
State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150000, China.
Shandong Provincial Key Laboratory of Special Welding Technology, Harbin Institute of Technology at Weihai, Weihai 264209, China.
Materials (Basel). 2019 Aug 23;12(17):2703. doi: 10.3390/ma12172703.
Underwater laser beam welding (ULBW) with filler wire was applied to Ti-6Al-4V alloy. Process parameters including the back shielding gas flow rate (BSGFR) (the amount of protective gas flowing over the back of the workpiece per unit time), focal position, and laser power were investigated to obtain a high-quality butt joint. The results showed that the increase of BSGFR could obtain the slighter oxidation level and refiner crystal grain in the welded metals. Whereas the back shielding gas at a flow rate of 35 L/min resulting in pores in the welded metals. With the increasing of the heat input, the welded metals went through three stages, i.e., not full penetration, crystal grain refinement, and coarseness. Crystal grain refinement could improve the mechanical properties, however, not full penetration and pores led to the decline in mechanical properties. Under optimal process parameters, the microstructure in the fusion zones of the underwater and in-air weld metals was acicular martensite. The near the fusion zone of the underwater and in-air weld metals consisted of the α + α' phase, but almost without the α' phase in the near base metal zone. The tensile strength and impact toughness of the underwater welded joints were 852.81 MPa and 39.07 J/cm, respectively, which approached to those of the in-air welded joints (861.32 MPa and 38.99 J/cm).
采用填丝水下激光束焊接（ULBW）工艺对Ti-6Al-4V合金进行焊接。研究了包括背面保护气体流量（BSGFR）（单位时间内流过工件背面的保护气体量）、焦点位置和激光功率在内的工艺参数，以获得高质量的对接接头。结果表明，增加BSGFR可使焊接金属中的氧化程度更轻，晶粒更细化。而当背面保护气体流量为35L/min时，焊接金属中出现气孔。随着热输入的增加，焊接金属经历了未完全熔透、晶粒细化和粗化三个阶段。晶粒细化可改善力学性能，然而，未完全熔透和气孔会导致力学性能下降。在最佳工艺参数下，水下和空气中焊接金属熔合区的微观组织为针状马氏体。水下和空气中焊接金属熔合区附近由α + α'相组成，但在近母材区几乎没有α'相。水下焊接接头的抗拉强度和冲击韧性分别为852.81MPa和39.07J/cm，接近空气中焊接接头的抗拉强度（861.32MPa）和冲击韧性（38.99J/cm）。
