Interfacial behaviors and joint properties of the dual beam laser fusion brazing Ti6Al4V/AA7075 dissimilar metals

Abstract

The AA7075 aluminum alloy with Ti6Al4V titanium alloy in lap configuration was successfully joined with laser fusion brazing method without filler wire. The effects of laser fusion brazing parameters, including defocus distance and laser power, on the joint appearance, interfacial microstructure and mechanical properties of the joints were explored. The results indicated that a good joint appearance could be obtained with variation of defocus distances. The adjustable range of laser power was expanded with the increase of defocus distance, from the range of 1600-1800 W with the laser spot diameter of 1.0 mm (defocus distance of +10 mm) to 2600 W–3400 W with the laser spot diameter of 2.7 mm (defocus distance of +20 mm). It was observed that the wettability of molten aluminum alloy on titanium alloy was improved with the increase of laser power, the wetting length was increased from 1.76 mm to 3.62 mm and the contact angle was decreased from 32.8° to 21.6° upon increasing the total laser power from 2400 W to 3000 W with the defocus distance of +15 mm. There was a continuous 0.7 ± 0.2 μm thick TiAl3 IMC (intermetallic compound) layer at the brazing interface with the defocus distance of +15 mm and laser power of 3000 W. The tensile strength and fracture location of the joints were mainly dependent on the spreadability and IMC thickness along the interface. Poor spreadability and too thick IMC thickness at the inner part of interface will result in fracture along the Al/Ti interface and lower strength. The best mechanical properties of the joints with the fracture load of 3621 N on average could be obtained with the defocus distance of +20 mm and laser power of 3400 W.