Research On Welding-riveting-bonding Hybrid Joining Technology Of High Strength Steels And Aluminum Alloy

With the increasingly serious energy and environmental problems in the world,energy-saving and emission reduction have become an urgent goal in the development of the automobile industry.An important way to achieve energy saving and emission reduction is vehicle lightweight,that is to reduce vehicle weight as much as possible on the premise of ensuring strength and safety performance.This method can improve the power performance of the car,save fuel and reduce exhaust emissions.An effective way to lighten automobiles is to increase the use of lightweight materials.Aluminum alloys and high-strength steels have become popular materials in automobile manufacturing due to their respective advantages.However,because of the differences in physical and chemical properties between Al and Fe,it is difficult to weld them directly.Therefore,researchers have researched the high-quality joining of steel/Al given this difficulty.To solve the problem that a large number of intermetallic compounds were produced during the direct welding of steel and Al,the welding-riveting hybrid joining process was proposed.By introducing the rivet into the joining of steel sheet and aluminum sheet,the main part bearing tension and shear load changed from the steel/Al interface with weak performance in direct welding to the steel/rivet bonding area with better performance in welding-riveting joining.Firstly,Q460 high strength steel and 6061 aluminum alloy were joined by the“steel on top and aluminum on bottom”method.The effects of laser power on weld formation,mechanical properties,and microstructures were investigated.The optimal laser parameter was determined,and the joining mechanism of the steel/Al interface under the optimal parameter was revealed.To further improve the mechanical properties of the joint,the third generation advanced high strength steel QP980 and 6061 aluminum alloy were used for welding-riveting joining,and the best joint was obtained by changing the welding parameters.Finally,on this basis,the adhesive layer was added in the lap joint area to further optimize the comprehensive performance of the steel/Al joint,and the mechanism of the adhesive layer in improving the joint performance was described.The results showed that the reliable joining between high-strength steels and aluminum alloy can be realized through laser induced arc hybrid welding heat source and welding-riveting process.For Q460/6061 welding-riveting joint,the average maximum tensile shear load was6.3k N,and the corresponding fracture mode was“pull-out fracture”.For QP980/6061 welding-riveting joint,the maximum tensile and shear load could reach 7.15k N,which was 13.5%higher than that of the former.The steel/Al interface of the welding-riveting joint was composed of Fe₂Al₅,Fe₄Al₁₃ distributed on Fe₂Al₅,and Fe₄Al₁₃ free in the aluminum matrix.By adding the adhesive layer,the mechanical properties of the QP980/6061 joint were further improved by22.3%,the fracture mode was“pull-out fracture”,and the plasticity and toughness of the joint were also improved.The gas generated by the adhesive layer during the welding process increased the stirring effect on the molten pool,making the steel and aluminum mixed more evenly,the microstructure and hardness distribution of the weld fusion zone also tended to be uniform.And the free Fe₄Al₁₃ at the steel/Al interface disappeared,which greatly reduced the existing area of intermetallic compounds,which was conducive to improving the properties of the joint.Besides,the mechanical properties of the QP980/6061 joint in a corrosive environment could be maintained by adding an adhesive layer.