Effect of alloying elements on filler metal for brazing of 70% SiC_P/Al composites

The content of Cu, Si, Mg and Ni was changed by using orthogonal experiment in order to study how the content effected on the melting point and wettablity of Al-Cu-Si-Mg-Ni filler metal. The microstructure of the filler metal was analyzed by SEM and EDS. There were three factors affecting the melting point of filler metal, namely, the content of Mg element, the Al-Cu-Si eutectic reaction and the content of Ni element in proper order. With increasing of Mg content, the wettability was improved, but excess Mg led to the increase of porosity when the Mg content was constant, the closer the ratio of (Si/Cu) to (Si+Cu) to 0.06 was, the more Al-Cu-Si eutectic reaction occured. When the Mg content and Al-Cu-Si eutectic reaction were constant, the melting point decreased with the addition of Ni. Coarse blocky Si phase generated along grain boundaries could induce the joint brittle. Pore was built up around silicon-rich phase which was generated in a few areas as a result of Si segregation. Dispersed white needles θ(CuAl₂) phase also decreased the strength of welding joint to some extent. However, α solid solution(Al-Cu、Al-Cu-Si and Al-Si)with face-centered cubic structure improved mechanical properties of the filler metal.