镁合金变极性等离子弧焊接头的微观组织分析

采用变极性等离子弧焊接实现了AZ31B变形镁合金板材的优质连接,焊后利用光学显微镜、电子探针 (EPMA)和X射线衍射(XRD)仪对焊接接头的微观组织、元素分布以及相组成进行了分析。结果表明,镁合金变极性等离子弧焊接头中没有明显的热影响区存在,接头成形好,焊缝组织均匀,晶粒细小;接头中主要的合金元素 Al、Zn在焊缝中分布均匀,没有发现区域偏析;接头中没有发现明显的Mg17Al12或其他杂质相的存在;由于焊接过程中存在着镁的蒸发、烧损,导致接头硬度值在沿焊缝的横向和纵向两个方向上都稍有变化。变极性等离子弧焊方法能够改善镁合金焊接接头组织并提高接头的性能,是一种理想的提高镁合金焊接质量的方法。

ANALYSIS ON THE MICROSTRUCTURE OF VARIABLE POLARITY PLASMA ARC WELDING OF MAGNESIUM ALLOY

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 Mg_(17)Al_(12) 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.