Effects of zinc additions on the microstructure and melting temperatures of Al–Si–Cu filler metals

For the development of a low-melting-point filler metal for brazing aluminum alloys, a series of Al–Si–Cu–Zn alloys has been studied. Through differential thermal analysis (DTA) analysis, the melting temperatures of such Al–Si–Cu–Zn filler metals were determined. The results show that the addition of 10–30 wt.% copper into the traditional Al–12 wt.% Si filler metal causes its solidus temperature to decrease by about 60 °C. An addition of 10–30 wt.% zinc into such Al–Si–Cu ternary alloys will cause their solidus temperatures to drop further to a value lower than 500 °C. Metallographic observations indicate that the addition of zinc into the Al–Si–Cu alloys inhibits the formation of the Al–Si, Al–Cu and Al–Si–Cu eutectic phases. The remaining phases are a CuAl2 intermetallic compound, an α-Al solid solution and silicon particles.