Steel has been mainly used in the automotive industry, because of good mechanical properties, weldability and so on. However, there has been increase in using aluminum to decrease the weight of vehicle. This leads to improve fuel efficiency and to reduce air pollution. A steel-aluminum hybrid body structure is recently used not only to reduce the weight of vehicle but also to increase safety.
In this paper, the laser beam joining method is suggested to join steel and aluminum. To avoid making brittle intermetallic compounds(IMC) that reduce mechanical properties of the joint area, only aluminum is melted by laser irradiation and wetted on the steel surface. The brittle IMC layer is formed with small thickness at the interface between steel and aluminum. By controlling the process parameters, brittle IMC layer thickness is suppressed under 10 micrometers which is a criterion to maintain good mechanical properties.
Thermal finite element analysis(FEA) is conducted. The molten area of base metals are analyzed by FEA results and compared with experiment. Temperature data from FEA results are used to find IMC layer thickness analytically at the interface.
IMC layer is established as a function of time and temperature when there is interaction between solid steel and molten aluminum. The IMC layer thickness is obtained by cumulative computation using the time-temperature data from FEA results.
