Effect of strontium and SmO on the microstructure and fracture mode of AlSi-Mg₂Si brazing filler metal

杨拓宇^1,2，张德库¹，王克鸿¹，黄俊¹

1. School of Material Science & Engineering, Nanjing University of Science and Technology2. School of Mechanical Engineering,Anhui Science and Technology University

摘 要：An AlSi-Mg₂Si self-fluxing brazing filler metal was obtained by activating Al Si brazing filler metal with the Mg₂Si phase and applying a metamorphism treatment of Mg₂Si and Si crystals with Sr and Sm O. A good wetting performance between the modified AlSi-Mg₂ Si and 3003 Al alloys was achieved in the vacuum brazing without Mg vapour as the activator. The melting point of the brazing filler was measured by STA409 Pc differential scanning calorimetry. A scanning electron microscope was used to analyse the microstructure and the component distribution of the brazing filler. The results indicated that the change in morphology of the Mg₂ Si phase was remarkable after metamorphism. The analyses of the microstructure indicated that the Mg₂ Si and Si phases presented small needle-type and granular morphologies. The follows were found to occur: intergranular penetration of Mg and Si on the base metal, a large amount of granular eutectic structure, and a significant grain boundary effect. The shear fracture of the lap joint presented cleavage fracture; in addition, with the decrease of the Mg₂ Si phases, the fracture morphology transformed from a rock candy shape to a steam shape, and cleavage steps appeared. The rock candy-shaped fracture areas enlarged after metamorphism treatment.

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