Development of Al–Si–Zn–Sr filler metals for brazing 6061 aluminum alloy

To develop new aluminum filler metals used for brazing 6061 alloy, the microstructure and properties of Al–6.5Si–42Zn–xSr alloys with different Sr content were studied. The results showed that the melting point of Al–6.5Si–42Zn alloy is around 520 °C, and Sr addition did not change the melting point of the filler metals, yet trace amounts of them greatly improved the microstructure of the alloys. As Sr content increased, the number of primary Si particles decreased and the eutectic Si changed from acicular to fine fibrous morphology in the Al–6.5Si–42Zn–xSr alloys. Meanwhile, Sr also refined the β-Fe intermetallic compound in the alloy. The wettability of the Al–6.5Si–42Zn–xSr brazing alloys improved with increasing Sr content, in addition, it was found that Sr addition also modified the microstructure of the brazing joints. From the tensile test results, the strength of the lap joints and the butt joints could be increased by 14% and 11%.

► Low-temperature filler metals were designed for aluminum alloy 6061 brazing.
► Significant changes in the microstructure of the filler metal with increasing Sr content.
► Sr addition improved the morphology and distribution of β-Fe phase in the filler metal.
► Sr addition improved the wettability of the filler metals as well as the strength of 6061 Al brazing joints.