Study On The Effect Of Thermal On Joining Steels And Aluminum Alloys

In recent years, with the increase of the number of domestic automobile productions, the problems of exhaust pollution, energy shortages have become the focus of attention of the international community. Lightweight design is one of efficient methods to realize energy conservation and emission reduction. Steel-aluminum hybrid car-body structures is the most common approach to weight reduction in the car body among car manufactures. Comparing to the traditional car body, Steel-aluminum hybrid car-body structure is that some parts are replaced by lightweight materials, such as high strength steel, aluminum alloy sheets and so on, to meet the requirements for the high-strength and lightweight. But because of large differences of the coefficient of thermal expansion between steel and aluminum, there is a large difference between the thermal expansion of aluminum and steel during automobile coating process. Just for this reason steel-aluminum hybrid car-body structure may have large thermal deformation, which may lead to buckling deformation so that the failure occurs during assembly. What’s more, the thermal deformation could cause failure of steel / aluminum dissimilar materials joint. So it is quite necessary to analyze the influence factors of steel-aluminum hybrid car-body structure under the automobile coating environment.The materials that this article chose is Q235 carbon steel and 5754 aluminum alloy. The thermal expansion coefficient of Q235 carbon steel and 5754 aluminum alloy were obtained through the experiment, which present the changes of thermal expansion coefficient with temperature. Finite element(FE) simulation analysis were carried out to study the thermal expansion of aluminum and steel. And verified the feasibility of the FE model through theories of the coefficient of thermal expansion.Based on the feasibility of theories verification, a finite element model during automobile coating process was established for modeling of steel/aluminum adhesive joints. Firstly, chose the simulation methods of adhesive joints, and verified the feasibility of the FE model through steel /aluminum bonding experiment. Then the influence of metal thickness and adhesive thickness on the strength of joints and the influence of metal thickness, adhesive width, Elastic Modulus of adhesive on the thermal deformation of steel /aluminum bonding were studied.Based on the FE model of the thermal expansion of aluminum and steel, in this thesis a model under the automobile coating environment was carried out to study the joins strength of joining steel sheet and aluminum sheet by using mechanical clinching. The influence of the place order of steel sheet and aluminum sheet on the strength of mechanical clinching was studied. The conclusion provided a reference for improving the strength of steel-aluminum sheet’ mechanical clinching after coating process, and reducing the thermal deformation of steel-aluminum hybrid car-body structure.