ANALYSIS ON THE Microstructure of Variable polarity plasma arc weldING OF magnesium alloy

LIU Liming  SHEN Yong  ZHANG Zhaodong

(State Key Laboratory of Material Surface Modification by Laser, Ion, and Electronic Beams, Dalian University of Technology,Dalian 116024)

Abstract: With high productivity, easy adjustment of welding parameters and free of weld defects, the variable polarity plasma arc welding process that is made up of variable square wave welding power source is used successfully to weld the wrought magnesium alloy AZ31B. The microstructure characteristics of the weld are investigated by the optical microscope, electron probe microanalysis (EPMA) and X-ray diffraction. At the same time, the micro-hardness of the joint is also measured by the instrument. The results show that the heat-affected zone within joint is not evident, and the grains of fusion zone (FZ) are tiny. Besides, the distribution of element Al and Zn are even in the joint in spite of the vaporizing of Mg. The element segregation and Mg17Al12 phase can not be found in FZ. The micro-hardness in FZ exist a little change than that of the parent metal due to the evaporation of Mg element both in longitudinal and transverse direction. In summary, the variable polarity plasma arc welding process is a perfect welding method which can improve the microstructure of joint and increase the welding quality.

Key words: Variable polarity plasma arc   Magnesium alloy   Microstructure

CLC No: TG456

教育部优秀青年教师基金和教育部新世纪优秀人才支持计划(NCET-04-0271)资助项目. Received 20050528, received in revised form 20051120