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Research Papers

Microstructure and Fatigue Property of Ti–6Al–4V by Ultrahigh Frequency Pulse Welding

[+] Author and Article Information
Mingxuan Yang

School of Mechanical
Engineering and Automation,
Beijing University of
Aeronautics and Astronautics,
No. 37, Xueyuan Road,
Haidian District,
Beijing 100191, China
e-mail: yangmingxuan@buaa.edu.cn

Hao Zheng, Bojin Qi

School of Mechanical
Engineering and Automation,
Beijing University of
Aeronautics and Astronautics,
No.37, Xueyuan Road,
Haidian District,
Beijing 100191, China

Zhou Yang

Department of Mechanical Engineering,
Tsinghua University,
Beijing 100084, China

1Corresponding author.

Manuscript received March 10, 2016; final manuscript received September 30, 2016; published online November 9, 2016. Assoc. Editor: Wayne Cai.

J. Manuf. Sci. Eng 139(4), 041015 (Nov 09, 2016) (8 pages) Paper No: MANU-16-1156; doi: 10.1115/1.4035036 History: Received March 10, 2016; Revised September 30, 2016

Butt welding tests of 1.5 mm thickness Ti–6Al–4V were treated by conventional gas tungsten arc welding (C-GTAW) and ultrahigh frequency pulse GTAW (UHFP-GTAW). The low cycle fatigue (LCF) experiments were conducted on the welded joints. The results of fatigue experiment showed that the number of fatigue cycles was increased with UHFP-GTAW. Changes in the microstructure resulting from reduced heat input were expected to enhance the fatigue propagation resistance. The morphology of the martensites in fusion zone was smaller compared to C-GTAW process, and a larger distribution density of basketweave structure was also obtained by UHFP-GTAW. Furthermore, the decreased fatigue crack rate was accompanied as the increased grain boundaries produced by the reduced grain size in fusion zone. Observation of fatigue fractographs revealed that the UHFP-GTAW has obvious slip traces at fatigue initiation sites and more deep secondary cracks in the crack propagation regions associated with the smaller dimples of final fracture zones. The proportion of propagation regions was much larger than C-GTAW. As a result, it can be considered as the representation of the improvement in ductility.

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References

Figures

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Fig. 1

Equipment and schematic of the weld current waveform

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Fig. 2

Sketch map of specimen preparation

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Fig. 3

Geometry of a typical axial fatigue specimen

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Fig. 12

Microscopic morphology of final failure (a) C-GTAW, (b) UHFP-GTAW (f = 50 kHz), (c)C-GTAW, and (d) UHFP-GTAW (f = 50 kHz)

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Fig. 11

Fatigue striations and secondary crack (a) C-GTAW and (b) UHFP-GTAW (f = 60 kHz)

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Fig. 10

Microscopic morphology of crack propagation (a) C-GTAW, (b) UHFP-GTAW (f = 70 kHz), (c) C-GTAW, and (d) UHFP-GTAW (f = 60 kHz)

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Fig. 9

Microscopic morphology of crack initiation (a) C-GTAW and (b) UHFP-GTAW (f = 70 kHz)

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Fig. 8

Macroscopic morphology of fatigue fracture (a) C-GTAW and (b) UHFP-GTAW (f = 30 kHz)

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Fig. 7

Correlation between the number of fatigue cycles and grain size in fusion zone with the variation of pulse frequency (a) fatigue cycles and grain size against pulse frequency and (b) the ratio of fatigue cycles to grain size against pulse frequency

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Fig. 6

Top views of microstructure in fusion zone (a) C-GTAW and (b) UHFP-GTAW (f = 10 kHz)

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Fig. 5

Cross-sectional optical micrographs of fusion zone (a) C-GTAW and (b) UHFP-GTAW (f = 10 kHz)

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Fig. 4

Correlation between the number of fatigue cycles and heat input with the variation of pulse frequency

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