Chen Qihao, Lin Sanbao, Yang Chunli, Fan Chenglei, Ge Hongliang
State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001, PR China.
State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001, PR China.
Ultrason Sonochem. 2017 Nov;39:403-413. doi: 10.1016/j.ultsonch.2017.05.001. Epub 2017 May 3.
Under the action of acoustic waves during an ultrasonic-assisted tungsten inert gas (TIG) welding process, a grain of a TIG weld of aluminum alloy is refined by nucleation and grain fragmentation. Herein, effects of ultrasound on grain fragmentation in the TIG weld of aluminum alloy are investigated via systematic welding experiments of pure aluminum. First, experiments involving continuous and fixed-position welding are performed, which demonstrate that ultrasound can break the grain of the TIG weld of pure aluminum. The microstructural characteristics of an ultrasonic-assisted TIG weld fabricated by fixed-position welding are analyzed. The microstructure is found to transform from plane crystal, columnar crystal, and uniform equiaxed crystal into plane crystal, deformed columnar crystal, and nonuniform equiaxed crystal after application of ultrasound. Second, factors influencing ultrasonic grain fragmentation are investigated. The ultrasonic amplitude and welding current are found to have a considerable effect on grain fragmentation. The degree of fragmentation first increases and then decreases with an increase in ultrasonic amplitude, and it increases with an increase in welding current. Measurement results of the vibration of the weld pool show that the degree of grain fragmentation is related to the intensity of acoustic nonlinearity in the weld pool. The greater the intensity of acoustic nonlinearity, the greater is the degree of grain fragmentation. Finally, the mechanism of ultrasonic grain fragmentation in the TIG weld of pure aluminum is discussed. A finite element simulation is used to simulate the acoustic pressure and flow in the weld pool. The acoustic pressure in the weld pool exceeds the cavitation threshold, and cavitation bubbles are generated. The flow velocity in the weld pool does not change noticeably after application of ultrasound. It is concluded that the high-pressure conditions induced during the occurrence of cavitation, lead to grain fragmentation in a pure aluminum TIG weld during an ultrasonic-assisted TIG welding process.
在超声辅助钨极惰性气体保护（TIG）焊接过程中的声波作用下，铝合金TIG焊缝的晶粒通过形核和晶粒破碎得到细化。在此，通过纯铝的系统焊接实验研究了超声对铝合金TIG焊缝中晶粒破碎的影响。首先，进行了连续和定位焊接实验，结果表明超声能够破碎纯铝TIG焊缝的晶粒。分析了定位焊接制备的超声辅助TIG焊缝的微观结构特征。发现施加超声后，微观结构从平面晶体、柱状晶体和均匀等轴晶体转变为平面晶体、变形柱状晶体和不均匀等轴晶体。其次，研究了影响超声晶粒破碎的因素。发现超声振幅和焊接电流对晶粒破碎有显著影响。随着超声振幅的增加，破碎程度先增大后减小，且随着焊接电流的增加而增大。熔池振动的测量结果表明，晶粒破碎程度与熔池中的声非线性强度有关。声非线性强度越大，晶粒破碎程度越大。最后，讨论了纯铝TIG焊缝中超声晶粒破碎的机制。使用有限元模拟来模拟熔池中的声压和流动。熔池中的声压超过空化阈值，产生空化气泡。施加超声后，熔池中的流速没有明显变化。得出结论，在超声辅助TIG焊接过程中，空化发生时产生的高压条件导致纯铝TIG焊缝中的晶粒破碎。
