Investigation on Formation and Corrosion of the Interfacein Aluminum Eutectic Reaction Brazing

In this paper,some problems about the formation of the brazed seam interface and its electrochemical corrosion resistance properties were investigated by using a scanning electron microscope and an electron probe.The results showed that,if only using Zn as the layer in Al eutectic reaction brazing, the eutectic liquid phase can not make the parent metal wet and can not form a good brazed seam interface and that Zn can cause erosion to Al. It also showed that,if adding Cu between Al and Zn,Cu can take priority of gathering and diffusing in the surface crystal boundary of the parent metal and take the eutectic reaction with Al to form an Al-Cu eutectic liquid phase. Furthermore the Al-Cu eutectic liquid phase can make the surface Al oxide film rise,move,break and wet,spread on the all brazed seam surface， then Zn can be dissolved into the Al-Cu eutectic liquid phase and the Al-Zn-Cu eutectic liquid phase interface can be gradually formed and wetted, spread on the all Al brazed seam surface as the temperature increases and the time passes. Adding Cu between Al and Zn can effectively destroy the Al oxide film on the parent metal,prevent Zn from corroding Al,make Zn wet and spread on all brazed seam surface and form a good Al-Zn-Cu eutectic reaction brazed seam surface. While used Cu-Zn as the layer,the difference of the electrode potentials between the formed Al-Zn-Cu eutectic and the parent metal is small. The electrochemical corrosion resistance properties by using Cu-Zn as the layer are better than those by using Cu. As the Cu content increases,the electrochemical corrosion resistance properties decrease. The corrosion can take place firstly in the rich Cu zone along the Al crystal boundary in the parent metal.