Joining Technique for light Weight Al-Steel Hybrid StructureThursday (09.11.2017) 15:20 - 15:40 Part of:
Multi-material design with Al-Steel-FRP is the most efficient way to achieve an affordable lightweight vehicle, but requires many new joining techniques such as self piercing riveting, adhesive bonding etc., which need big invest into new assembly equipment and generate high risks of the project. It restricts the usage of light materials in body in white.
To solve this problem, two new joining methods were developed and will be presented, which enable the usage of the existing welding equipment in the assembly line. It may promote the application of light weight materials like Al.
First, based on the knowledge of intermetallic alloys, the interdiffusion between steel and Al, a new Al-Si-coating with special chem. composition and layer design were developed for steel sheet parts as they are hybrid casted by Al. The steel inserts in Al-cast enable the welding between Al and steel indirectly. This new coating comprises two sublayers. The first layer is less than 3 μm in thickness and consists of Fe, Si as well as lower Al-content. The main layer consists only of Al and Si. With this coating a highly ductile joining between steel and Al can be produced during an Al-steel hybrid casting process with a special developed process and die design. The strength of this diffusion induced material based joining is more than 10 MPa and comparable with adhesive bonding. The deformation and fracture mechanism of this material connection were analyzed by mechanical testing and SEM.
Using the second method, rivet resistance spot welding, sheets metal parts of different materials e.g. Al, Steel and FRP can be joined reliably on the spot welding line without changing any existing facilities. A steel-rivet is pressed into Al sheet part (an Al-rivet into a FRP part) during its forming process. The rivets are used as a welding medium. So Al and steel parts can be spot welded directly. With a special design of rivet, a small gap between welded parts can be generated after joining which prevent the galvanic corrosion between different materials. The static and dynamic properties of the new joint are excellent. Besides rivet development, experimental results, manufacturing of an Al car roof and FEM simulation for predicting the joining properties will be presented and discussed.