Study On Resistance Spot Welding Between Aluminum Alloy A6061 And Mild Steel Q235 With A Medium

In recent years, for the sake of achieving the sustainable development of human society, people attach more and more importance to energy saving and emission reduction. Therefore, low-carbon economy has become a genal trend of world economic development. It has become an inevitable choice for the automobile lightweight to realize the coordinated development between the high speed development of aotumobile industry and low carbon emissions, establishing the environment –friendly society in China. In order to mitigate the body weight of the car, the light alloy materials gradually replace the steels as the main material. Hense, joining aluminum to steel is essential. However, because of the difference between aluminum and steel in physics, metallurgical properties, it is difficult to use the conventional welding methods to realize their connection perfectly.This research adopted the methods that aluminum alloy A6061 and low carbon steel Q235 sheets were welded using resistance spot welding with an interlayer of Al86Si6Mg8 and Al Si12. The characters of the microstructures on the nano-scale bonding interface of steel-aluminum alloy were observed and analyzed by the use of optical microscope and scanning electron microscope(SEM). It also investigated the welding current, welding time and electrode force had impact on the nugget size and tensile shear strength. On these basises, this thesis studied the effect of interface structure to joint performance and developed a resistance spot weiding with a rivet used for the spot welding of aluminum and steel. As well as, it studied the joint structure and performance of aluminum-steel resistance spot welding with a rivet.For three kinds of resistance spot welding between aluminum alloy and steel, resistance spot welding without interlayer, resistance spot welding with Al86Si6Mg8 layer and resistance spot welding with AlSi12 layer, it was observed that a ribbon reaction layer consisting of Fe2Al5 and Fe Al3 forms in the welding interface and that the reaction layer thickness varies with the position at the welding interface. The results reveal that inhibiting the growth of the interfacial intermetallic compound can be achieved by using Al86Si6Mg8 and Al Si12 filler metals as medium for resistance spot welding between aluminum alloy and steel, and that the effect of Al Si12 filler metals is better.Maximum tensile shear load of joint welded by resistance spot welding without interlayer, resistance spot welding with Al86Si6Mg8 layer and with Al Si12 layer is 4.5 kN, 5.2 kN and 4.75 kN, respectively. The results reveal that adding silicon-based alloy can effectively improve the aluminum alloy/steel joint performance, but higher Si content can cause the tensile shear load of joint reduce.Resistance rivet-welding of aluminum alloy and steel shows that the presence of an FeAl reaction layer at the rivet/aluminum alloy interface, and of FeAl3 at the steel/aluminum alloy interface, and that a tensile shear load of 4.1k N was obtained at a welding current of 21 kA. The results reveal that resistance spot welding with a rivet is an effective method for joining steel and aluminum alloy.