Crack analysis near vacuum brazing interface of Cu/Al dissimilar materials using Al-Si brazing alloy.

The present paper concentrates on the factors inducing cracking near the Cu/Al vacuum brazing interface using Al-Si brazing alloy. Various analysis and test methods were adopted to analyse the cause of the cracking. Experiment results indicated that two intermetallic compounds layers -- δ phase and θ phase -- were formed near the interface of Cu and brazing seam region. The microhardness of both the two intermetallic compounds phases reached 720 and 510 HM respectively. The brazing seam region consisted mainly of θ phase and α-Al (Cu) solid solution. Si presence had led to obvious zone liquation in the brazing seam region. Stress concentration appeared on the margin and edge region of the joint. The crack initiated on the θ phase layer, and then extended towards the brazing seam region and δ phase layer. The separation in the d phase had an obviously brittle fracture surface. [ABSTRACT FROM AUTHOR]