Energy Condition And Its Influence In Brazing-fusion Welding Of Al Alloy To Galvanized Steel

As a new joining method of dissimilar metals with high efficiency, high quality and flexibility, brazing-fusion welding technology has been a hot spot in joining of aluminum to steel. Technological experiment and thermal process are of critical significance for optimizing welding parameters and promoting the application of hybrid structures of aluminum and steel.1mm6013-T4and5A02aluminum alloy plates were lap joined to2mm galvanized steel plates by MIG arc and large spot laser-MIG arc hybrid welding with AlSi5filler metal. The effects of welding parameters on weld shape, microstructures and mechanical properties were investigated, especially for the influence of weld heat input on Fe-Al intermetallic compounds. Finite element models of MIG arc and laser-MIG arc hybrid welding process were established, and the welding heat input parameters range were calculated based on the temperature field. Finally, the effects of lager spot laser on laser-MIG arc hybrid welding were discussed according to the results of experiment and simulation.The experimental results indicated that the good joints of6013-T4aluminum alloy and galvanized steel can been obtained successfully by MIG arc brazing-fusion welding. The weld appearances is better at welding speed v<lm/min when the heat input is850J/cm, and the tensile strength of joint can reach229MPa, about50%of base matal of6013-T4Al alloy. However, high efficiency and high quality joining of aluminum to steel can been achieved by lager spot laser-MIG arc hybrid welding, and the highest speed can be up to6m/min, the highest tensile strength of joint can reach247.3MPa, the mean tensile strength about85%of base metal, and the fracture occurres near the heat affected zone of Al alloy fusion weld. Brazed-fusion welded joint can be divided into fusion zone, interface reaction zone and zinc-riched zone. Fusion zone is composed of α-Al and Al-Si eutectic. The thickness of interface layer is about0.8～6μm, increased with the increase of heat input. Intermetallic compounds (IMCs) layer is composed of compact FeAl2and Fe2Al5near the steel surface, and Fe4Al13which presents "saw teeth" or "acerose" toward the weld metal. Zinc-riched zone consists of Al-Zn solid solution, Al-Zn eutectic and Al-Zn eutectoid. When the thickness of IMCs layer exceeds2μm, the brazed interface between Al alloy and steel was not the weakest zone in brazed-fusion welded joint.The thermal process of MIG arc and laser-MIG arc hybrid brazing-fusion welding were analyzed, and their finite element model was established for lap joint. The effects of zinc coating, lap gap, backfilling plate on temperature field were considered. The appropriate heat source models for brazing-fusion welding were established by considering the arc, laser and droplets heat. Weld shape and the heat affected zone width of zinc coating on the back side of galvanized steel plate were used to validate the calculated results. The results show that the calculated results and that of experiments are in good agreement. According to analysis on the brazed interface and the calculated corresponding relationship between the temperature field on the brazed interface and the interfacial reaction, the brazed interface can be divided into three zones such as strong interfacial reaction zone, weak interfacial reaction zone and no interfacial reaction zone. The strong reaction zone is located in the center of the brazed interface and has a great influence on the properties of brazed-fusion joint, where the temperature is the highest, the reaction time is the longest and IMCs layer is the thicknest. The other zones with lower temeperature, thiner IMCs layer has a little influence on the properties of brazed-fusion joint. Then, the energy conditions were calculated based on interface peak temperature of brazed-fusion welded joints. Finally, the effects of lager spot laser in laser-MIG arc hybrid brazing-fusion welding were analyzed. The results indicate that lager spot laser can improve the spreadability of liquid Al alloy metal on the top surface of galvanized steel plate and make the weld appearance better through preheating steel. It can stabilize welding process and incarese welding speed by compressing and leading arc by plasma produced by zinc vapour.