Microstructure and mechanical properties of steel/aluminum circular oscillation laser welded joint

The lap welding experiments of DP590 dual phase steel and 6022 aluminum alloys were carried out by using circular oscillation laser. The mechanism of circular oscillation on the morphology, element distribution, grain size and mechanical properties of the molten pool was investigated through characterization experiments, theoretical calculations, numerical simulations and synchronous detection methods. The results showed that under the same heat input, the circular oscillation caused the heat to accumulate at the reversal point, forming an asymmetric "double molten pool" and increasing the bonding surface area. The metallurgical reaction between Fe and Al was suppressed by reducing the linear energy, and the layer thickness and phase composition of the interfacial intermetallic compounds (IMCs) were effectively regulated. The drag force generated by the "mango shaped" flow field improved the flow behavior of the molten pool, significantly enhancing the uniformity of element distribution and avoiding the formation of component segregation and solidification cracks. Based on the stirring effect of vortex, columnar crystals were broken and the temperature gradient was reduced to increase the nucleation point of equiaxed crystals, achieving remarkable grain refinement. The above experimental results are all beneficial for improving the mechanical properties of the joint, among which the thickness of the IMC layer at the interface is the key factor affecting the mechanical properties of the joint. The maximum shear tensile force (1325 N) of the joint was increased by 63.2%, and the corresponding fracture mode was changed from brittle fracture to ductile fracture.