Microstructure and mechanical properties of Al/steel metal by ultrasonic-assisted laser welding-brazing

Ultrasonic assisted laser welding-brazing technique was used for joining of 6061 aluminum alloy to steel dissimilar materials with AlSi filler metal. Effects of ultrasonic vibration on joint interfacial microstructure,grain size and mechanical properties of the weld were investigated. Without ultrasonic vibration,three layers of intermetallic compounds（ IMC） with the thickness range of 8. 3 ～ 12. 3 μm were observed in the heat source center of the interface between the weld and steel. The IMC thickness range away from the heat source was 1. 5 ～ 2. 6 μm. The joint strength was low and the joint failed at the interface of the weld and steel. When the ultrasonic power was 700 W,the spreading width of filler metal on the steel increased and the crystalline grain size decreased from 32 μm to 19 μm. The interfacial IMC was a continuous thin layer θ phase with a thickness of 0. 5 ～ 1. 0 μm. These changes led to the weld failure near aluminum fusion line and improved the joint strength by 1. 6 times of that without ultrasonic assisted.