Browsing by Author "Li, Zhuoxin"

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    Enhancing microstructural and mechanical characteristics of laser welded NiTi SMA/304 SS lap joints with medium and high entropy alloy fillers
    (Springer, 2024-01-03) Wang, Yipeng; Zhang, Dongni; Li, Hong; Li, Zhuoxin; Yang, Zijia; Chen, Xin; Cong, Baoqiang
    The demand for high-quality nickel-titanium (NiTi) shape memory alloy (SMA) and stainless steel (SS) welded structures has led to significant challenges in fusion welding technology, which is largely influenced by filler materials. This study explores the application of CoCrNi medium entropy alloy and CoCrNiFe high entropy alloy as filler materials for laser lap welding of NiTi SMA and 304 SS. A self-fusing joint was produced for comparison. The results demonstrate that the interface zone on the NiTi side was the weakest area regarding cracking defects in NiTi/304 SS lap joints. However, using CoCrNi and CoCrNiFe fillers effectively eliminated cracking defects by considerably suppressing the formation of brittle FeTi and Fe2Ti intermetallic compounds (IMCs). The average microhardness value of the weld zone without filler was higher than with CoCrNi and CoCrNiFe. Furthermore, the addition of CoCrNi and CoCrNiFe fillers to NiTi/304 SS lap joints resulted in a substantial increase in tensile properties, with tensile strength reaching 196 ± 39 MPa without filler, 319 ± 25 MPa with CoCrNi, and 377 ± 33 MPa with CoCrNiFe, respectively.
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    Refining microstructure of medium-thick AA2219 aluminium alloy welded joint by ultrasonic frequency double-pulsed arc
    (Elsevier, 2023-02-14) Wang, Yipeng; Li, Hong; Li, Zhuoxin; Zhang, Yu; Qin, Jian; Chen, Guangyu; Qi, Bojin; Zeng, Caiyou; Cong, Baoqiang
    The increasing demand for achieving high-efficiency and high-quality medium-thick aluminium alloy welded structures, especially for large scale aerospace components, presents an urgent challenge to the conventional TIG arc welding process. This work proposed a novel double-pulsed variable polarity tungsten inert gas (DP-VPTIG) arc, in which the variable polarity square wave current was simultaneously modulated into ultrasonic frequency (20–80 kHz) and low frequency (0.5–10 Hz) pulses. Full penetration welds of 6 mm thick AA2219 aluminum alloy were successfully obtained by using this process. The microstructure and mechanical properties of the weld produced by DP-VPTIG arc were investigated, taking the conventional VPTIG arc as a comparative study. Results show that the microstructure of weld zone by DP-VPTIG arc showed an alternating distribution of fine equiaxed grain band and slightly coarse equiaxed grain band. Compared to VPTIG arc, the grain structure was effectively refined in the weld zone with DP-VPTIG arc, showing a significant reduction of average grain size by 51.2% along transverse section and 61.3% along longitudinal section. The morphology of α-Al+θ-CuAl2 eutectics transformed from continuously distributed netlike shape to separately distributed granular shape, and segregation of Cu solute element was obviously improved. The average microhardness of weld zone was increased by about 8.7% and 5.6% along transverse section and along longitudinal section. The tensile properties of ultimate tensile strength, yield strength and elongation were increased by 6.6%, 10.6% and 20.5%, respectively. The results provide a valuable basis for improving welding efficiency and joint quality through a hybrid pulsed arc.