Effects of copper content on the microstructure and brazing properties of Al-Si-Cu-Zn-Re filler metals

The microstructure, phase constitution, melting character, and 6061 aluminum alloy brazing properties of Al-Si-Cu-Zn-Re filler metals with different copper contents were investigated. The Al-9.6Si-10Cu-10Zn-0.1Re, Al-9Si-15Cu-10Zn-0.1Re, and Al-8.4Si-20Cu-10Zn-0.1Re filler metals had the same solidus, at about 502 degrees C. Increasing the copper content lowered the liquidus temperature of the filler metals. In general, increasing the copper content and brazing time decreased the average joint shear strength of joints bonded with the Al-Si-Cu-Zn-Re filler metals. The joint strength of the 6061 aluminum alloy brazed with Al-9.6Si-10Cu-10Zn-0.1Re filler metal at 530 degrees C for 10 min without flux was about 72.9 MPa. All of the shear fractures occurred in the filler metals near the interface between the brazing alloy and the base metal. Due to the formation of Al2Cu intermetallic compounds and Si particles, the hardness values of the filler metals were higher than that of the 6061 aluminum substrate. Increasing the copper content in the filler metals also increased the width of the brazed joint regions with higher hardness.