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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.

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The objective of this study was to investigate the weldability of a new laminated material based on nichrome powder alloy using tungsten inert gas welding. Results revealed that nichrome-laminated powder alloy could be successfully joined by TIG welding. Two typical fusion zones were formed between different layers (Ni cover layer and nichrome base layer) and weld metal. Moreover, fusion zone of nichrome powder alloy was jagged due to the presented porosity. Between nichrome powder alloy and the filler metal, elements diffusion was obvious and a transition zone about 80-85 µm was formed. Microhardness near the fusion zone of nichrome base layer side (210-250 MPa) is higher than that near the fusion zone of Ni cover layer . Phase constitutions of the welded joint consisted mainly of γ-Fe, δ-ferrite and γ-Ni (Fe, Cr). Furthermore, co-existing microstructure of γ austenite and a small amount of δ ferrite was observed in the weld seam. K e y w o r d s : powder alloy, tungsten inert gas welding, fusion zone, fine structure