AZ91镁合金的半固态搅拌摩擦焊接连接形成机理

半固态连接被认为是一种连接合金的可能的方法。研究了AZ91镁合金半固态搅拌摩擦焊接的机理。将2块7.5 mm厚的AZ91镁合金试件和1块2 mm厚的 Mg?25%Zn中间层放在加热板上，加热到所需温度并保温3 min后，采用旋转搅拌头搅拌焊缝。将加热板在台车上以4.6 cm/min的恒定速度运动。同时，对一个样品进行无中间层焊接。使用扫描电子显微镜和光学显微镜研究焊接过程中搅拌速度、搅拌头形状和温度的影响。结果表明，中间层降低了焊接温度；升高温度、加快搅拌速度、采用圆形搅拌头代替槽形搅拌头都能增大搅拌区的宽度。在焊接过程中，可能存在某些机理，从而有助于获得良好的的冶金结合，例如氧化层消失、液相混合、液球连接、液体渗入基体、从大量液球基体金属进入焊缝区。

Mechanisms of joint formation throughout semisolid stir welding of AZ91 magnesium alloy

Joining in the semisolid state is considered a possible method to join alloys to each other. The mechanisms taking part in semisolid stir welding of AZ91 alloys were investigated. Two 7.5 mm-thick AZ91 pieces and a 2 mm-thick Mg-25%Zn interlayer piece were placed in a heating plate. After holding for 3 min at a desired temperature, the weld seam was stirred by a rotational tool. The heating plate was travelled on a trolley at a constant speed of 4.6 cm/min. In addition, one sample was welded without interlayer. Evolution of welding as a function of stirring rate, tool shape and temperature was studied throughout this welding process with scanning electron and optical microscopes. Interlayer decreases the joining temperature and assists to investigate the possible semisolid stir welding mechanisms. Increasing temperature and stirring rate, and using round stirrer instead of grooved stirrer increase the stir zone width. The results show that some possible mechanisms are helpful to achieve a proper metallurgical bonding in the welding process, such as oxide layer disruption, liquid phase blending, globule joining, and liquid penetration to the base metal, merging a group of globule into stir zone from the base metal.