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 θ phase had an obviously brittle fracture surface.
Dissimilar metals of copper (T2) and aluminium (1035) were brazed by vacuum brazing technology. Microstructure and phase constitution for the Cu/Al vacuum brazing were studied by means of metallography, electron probe microanalyser and X-ray diffraction. Experiment results indicated that an obvious transition layer of copper based solution was formed near the interface of copper and braze metal. The brazing seam zone mainly consists of various solid solutions between many elements and a few intermetallic compounds which are hard and brittle. This is favourable to the enhancing of service performance of the Cu/Al brazed joint. Process parameters of vacuum brazing are: brazing temperature T5425uC, vacuum level510 23 Pa, holding time t515 min.
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