镁铝异种材料TIG焊接接头扩散行为分析

Diffusion behaviour analysis of TIG welded joint between dissimilar materials Mg and Al

利用现代分析测试手段分别研究了TIG焊直接焊接镁铝和镀锡焊接镁铝的焊缝熔合区形貌,并对其进行了元素扩散行为的分析及比较。结果表明镁铝直接焊接时,镁与铝之间有明显的界面,镁元素向铝母材中进行大量扩散形成扩散层,而铝元素向镁母材中的扩散很少,扩散到铝母材中的镁元素与铝形成Mg17A l126和β-A lMg金属间化合物,造成扩散层很容易发生断裂。镁铝镀锡焊接,采用熔焊—钎焊连接方法,中间过渡金属锡与母材之间形成了一个成分、组织和性能均不相同的过渡区,该区对接头性能有着较大的影响。锡层对镁铝接头产生拘束强化作用,过渡层比镁铝直接焊接要狭窄,并且尚余一些没有扩散的锡层,阻止了镁元素向铝母材中扩散。锡过渡层对镁与铝的直接接触起到了一定的阻碍作用。

Modern analytical methods have been used to investigate the patterns of fusion zone and the diffusion behaviors of elements by TIG direct welding and TIG with Sn as transition layer welding. The result shows that there is an obvious interface between Mg and Al base metal when they are welded directly. The element of Mg diffuses into Al base metal, and forms a diffusion layer, but at the same time there is only a little element of Al diffusing into Mg base metal. The Mg diffused into Al base metal can combine with Al and form Mg17Al12 and β-AlMg phases, which will cause the rupture of diffusion layer easily. TIG with Sn as transition layer welding, as a fusion-braze welding method, forms a Sn transition zone with different components, diffusion organizations and different performances between Sn and base metal. The Sn transition zone is narrower than the diffusion layer of TIG direct welding, which has brought constraining force on welded joint and hampered the diffusion of Mg element into Al base metal. The Sn transition zone takes the blocking effect on the direct contact between Mg and Al.