Effect of strontium on microstructure and properties of AlSi-Zn-xSr filler metals

The effect of zinc and strontium element on the spreadability, microstructure, and mechanical properties of Al-SiZn filler metal has been investigated. The results indicated that the spread area was increased by 51% with decreasing Zn content, and the tensile strength of the brazed 6061 aluminum alloy joint was gradually increased to 120.5MPa. With the addition of Sr, the spreadability of Al-Si-Zn filler metal was significantly improved, the number of primary Si particles decreased and the eutectic Si was changed from acicular to fine fibrous morphology distributed in a netlike form. The strength of 6061 aluminum alloy joint reached the peak value of 137.1 MPa when the content of Sr was 0.09%. The air-tightness test of the brazed pipe showed that the tightness of Al-0.2Si-77.8Zn and Al-2Si-62Zn were inferior to that of Al-6.5Si-42 Zn. After the immersion test, the tensile strength of Al-6.5Si-42 Zn filler metal was decreased by 4.6%, while the Al-6.5Si-42Zn-0.09 Sr filler metal was only by 3.6%.