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.%-5wt.%Sn into the Al-6Si-15 Cu filler metal causes its solidus temperature to decrease by about 12 ℃.The filler metal with the composition Al-6Si-l5Cu-2Ni is proposed,which possesses a melting temperature range of 512℃ to 520 ℃ and a microstructare 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 Al₂ Cu intermetallie compound,an α-Al solid solution and silicon particles.