Effects of element additions on the microstructure and mechanical properties 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-(Ni, Sn, Zn) filler metals have been studied. Through differential thermal analysis (DTA), the melting temperatures of such Al-Si-Cu-(Ni, Sn, Zn) filler metals were determined. The results show that the addition of 3 wt.%-5 wt.% Sn into the Al-6Si-15Cu filler metal causes its solidus temperature to decrease by about 12℃. The filler metal with the composition Al-6Si-15Cu-2Ni is proposed, which possesses a melting temperature range of 512℃ to 520℃ and a microstructure that includes an Al-Cu eutectic phases, Al-Si-Cu eutectic phases, silicon particles and Cu₂Al, AlNi₃, Al₇Cu₄Ni and Al₃Ni₂ intermetallic compounds. An addition of 5 wt.%-7 wt.% Zn into such Al-Si-Cu filler metals cause their solidus temperatures to drop further to a value lower than 498℃. Metallographic observations indicate that the addition of Zn into the Al-Si-Cu filler metal inhibits the formation of the Al-Si, Al-Cu and Al-Si-Cu eutectic phases. The remaining phases are a Al₂Cu intermetallic compound, an α-Al solid solution and silicon particles.