Optimization of Laser Welded Joints of Steel/Al with Pre-placed High-Entropy Alloy Powder

This study optimized the laser welding process parameters of steel/Al by combining the Support Vector Machine model optimized by the Coati Optimization Algorithm (COA-SVM) with the Multi-Objective Cuckoo Search algorithm (MOCS), and the FeCoNiCrTi high-entropy alloy (HEA) powder was used as a filler metal to connect 5052 aluminum alloy with DP780 dual phase steel by laser welding. Using optical microscope and scanning electron microscope equipped with energy-dispersive spectroscopy to analyze the changes in joint structure and fracture morphology before and after adding HEA. The results showed that the optimized weld width decreased by 28.06% and the weld depth increased by 29.76%. The addition of HEA suppressed the Fe–Al mutual diffusion and significantly reduced the intermetallic compounds (IMCs) layer thickness. Some HEA elements participated in the reaction between Fe/Al, forming new phases such as Al₅FeNi, which increases ductility compared to the original phase. The maximum tensile force measured can reach 815 N. Compared with the absence of HEA, the maximum tensile force of the joint increased by 35.2%, and the fracture mode changed from brittle fracture to semi-brittle fracture.