Microstructure and Properties of Laser Oscillating Welding with Filler Wire of Thin Wall Titanium Alloy T-joints

doi:10.12382/bgxb.2021.0894

Abstract

Abstract:

In laser oscillating welding with filler wire, heat input is a key factor affecting microstructures and properties of the welded joint. Therefore, investigating the relationship between heat input and microstructures and properties can provide data support and theoretical basis for improving thin-wall titanium alloy welded joints. In this study, laser oscillating welding with filler wire is to join a 2mm thick TC4 titanium T-shape joint, and the microstructures and mechanical properties of different zones are analyzed. The result show that the weld surface is well-formed, with no defects such as incomplete fusion, pores, or slag inclusions. The weld microstructures are mainly composed of α' martensite phase and primary β phase, with a small amount of twins and dislocations. The heat-affected zone is mainly composed of α phase and α' martensite phase that have not undergone phase transformation in the base metal. The hardness value of the welded joint fluctuates between 286 and 413HV, and that of the weld zone is the highest, 38% higher than the base metal. With the increase of welding heat input, more α' martensite is formed due to phase transformation, and the microhardness increases as well. The average tensile strength of the welded joint is 1076MPa, which is slightly higher than that of the base metal. The fracture of the tensile specimen occurs at the base metal and shows characteristics of the ductile fracture. The average shear strength of the welded joint is 679MPa. The fracture starting position of the shear specimen is inside the weld, and the fracture in the weld zone shows characteristics of intergranular fracture. The fracture in the heat-affected zone displayed characteristics of cleavage and quasi-cleavage trans-granular fracture.

Key words: laser oscillating welding with flier wire, titanium alloy, T-joint, microstructure

WU Pengbo, XU Kai, HUANG Ruisheng, YANG Yicheng, ZOU Jipeng, CAO Hao. Microstructure and Properties of Laser Oscillating Welding with Filler Wire of Thin Wall Titanium Alloy T-joints[J]. Acta Armamentarii, 2023, 44(4): 1015-1022.

Figures/Tables 15

Fig.1 Microstructure of the titanium alloy base metal

Table 1 Mass fraction and properties of the base metal and welding wire in the test

材料	Al	V	Fe	C	N	H	O	Ti	抗拉强度R_m/MPa	显微硬度/HV
TC4钛合金	6.30	4.11	0.018	0.024	0.007	0.001	0.140	剩余	1038	286
TC4焊丝	5.75	3.82	0.044	0.012	0.006	0.001	0.081	剩余

Table 2 Processing parameters of laser oscillating welding with flier wire

激光功率/ kW	焊接速度/ (m·min^-1)	送丝速度/ (m·min^-1)	摆动方式	摆动频率/Hz	摆幅/ mm
4.5	0.8	3	圆形	100	1

Fig.2 Schematic diagram of the tensile specimen of welded joints

Fig.3 Shear specimen diagram of the welded joints

Fig.4 Macroscopic morphology and X-ray test results of T-type welded joints

Fig.5 Macroscopic morphology of the weld section

Fig.6 Microstructure morphology of welded joints in different regions

Fig.7 TEM morphology of the welding line

Fig.8 XRD analysis results of the weld zone

Fig.9 Microhardness of welded joints

Table 3 Tensile test of welded joints

试样编号	R_m/MPa		断裂位置
试样编号	数值	平均值	断裂位置
1-1	1071		母材区
1-2	1084	1076	母材区
1-3	1074		母材区

Fig.10 Tensile sample and SEM morphology of tensile fracture

Table 4 Mechanical performance test of welded joints

试样编号	剪切强度/MPa
试样编号	数值	平均值
2-1	682
2-2	685	679
2-3	671

Fig.11 Shear specimen and SEM morphology of shear fracture

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