Effect of Ti foil on microstructure and mechanical properties of laser fusion welding of DP590 dual-phase steel to 6022 aluminum alloy

The existence of brittle Fe-Al compounds restricts the performance of steel/aluminum joint. Adding Ti foil laser fusion welding of DP590 dual-phase steel to 6022 aluminum alloy was performed in an overlap steel-onaluminum configuration, and Ti foil was determined to improve the metallurgical reactions based on the calculated formation enthalpy, Gibbs free energy and ductility/brittleness. The effect of Ti foil on microstructure and properties of the steel/aluminum joint was investigated. Results showed that intermetallic compounds (IMCs), mainly ductile Fe2Ti and low-brittleness TiAl3 with high structural stability, were formed in steel side and aluminum side, respectively. The thickness of IMCs layer at the interface was reduced, which means that the reactions between Fe and Al were restrained and Fe-Al compounds were suppressed. The maximum load value reached 1616.25 N with 0.03 mm-thickness-Ti foil added, representing 27% enhancement compared with that with no-added. The improvement of mechanical properties assessed by tensile test and microhardness is in good agreement with the reduction of brittleness predicted from the calculation results, thus the mechanical properties of joints largely lie on the ductility/brittleness of IMCs. In addition, softening in heat affected zone (HAZ) was avoided in the upper dual-phase steel and grains on the molten pool were refined. Hence, the performance of steel/aluminum joint is significantly improved with the addition of Ti foil.