Investigation On Welding Technology Of Dissimilar Materials Between Aluminum And Steel

Hybrid structures of dissimilar materials between aluminum and steel can make use ofthe inherent advantages of two materials, such as light weight, high strength and highcorrosion-resistance, etc. They are used widely in the fields of automobile manufacture andaerospace vehicle. However, the joining of aluminum and steel is very difficult due to the lowsolid solubility, the great difference of thermal-physical and mechanical properties, as well asthe formation of brittle intermetallic compounds in the interfacial layer.In this thesis, MIG arc fusion-brazing and resistance spot welding technology werechosen to join aluminum to steel. The influence of different filler wires and the thickness ofgalvanized layer on the microstructures and mechanical properties of the joints wereinvestigated. The microstructure of the joint of aluminum/steel dissimilar metals resistancespot was researched. The effects of galvanized layer on the microstructure and mechanicalproperties of the resistance spot welded joints were studied.The results showed that the high quality welded joint of dissimilar metals betweenaluminum and steel was successfully achieved by MIG arc fusion-brazing welding technology.The welded joint was divided into weld zone, center interface zone, edge interface zone andzinc-rich zone. The growth of intermetallic compound layer (IMC) was suppressed due to theaddition of Si element and the thickness of IMC in the aluminum/steel interface was3-5μm,composed of Al3Fe, Al8Fe2Si and Al5Fe2phases with4043filler wire. The shear strength ofwelded joint was132.6MPa and the cracking position occurred in weld zone. When the fillerwire was5183, the thickness of the interface layer was6-8μm, which was composed of Al3Feand Al5Fe2phases. The shear strength of welded joint was67.9MPa and the cracking positionwas the aluminum/steel interface. Increment of galvanized layer thickness can improve shearstrength.The resistance spot welding joint of dissimilar materials of aluminum and steel wascomposed of heat affected zone and weld nugget. The intermetallic compound layer with unequal thickness was formed in the aluminum/steel interface zone, which was composed ofAl3Fe phase on aluminum side and Al5Fe2phase on steel side. When the galvanized layerexisted on the surface of steel, the temperature of aluminum/steel interface was reduced due tothe volatile zinc vapor, the growth of intermetallic compound layer (IMC) layer slowed down.The shear strength of welded joint was106.8MPa.