P 1133 – Development of hybrid joining technologies without pre-hole for ultra-high strength steels with tensile strength above 1.800 MPa in multi-material structures
The automobile industry focuses on light weight constructions because of the legal requirements to reduce the production of carbon dioxide. The decrease of carbon dioxide production to average 95g CO2/km in the passenger car market is determined until 2020.
Because of its 30% fraction of the gross vehicle weight the body in white has the biggest potential for light weight constructions using ultra high strength steel in thin sheet thicknesses and lightweight materials like aluminum. Especially the multi material construction of press hardened steel (22MnB5) and aluminum combined with the adhesive bonding leads to economical light-weight solutions. Even higher light weight grades can be achieved by using even stronger steels with strengths above 1800 MPa (in this report called as “UHSS+”). Thus, a further reduction of the material thickness can be achieved, wherein the component performance is substantially maintained.
The prerequisite for a UHSS+ construction in combination with aluminum structures is the applicability of cost-efficient and robust joining technologies. The aim of the research project is therefore the development of pre-hole free hybrid joining methods for multi material structures with novel steels with tensile strengths greater than 1,800 MPa.
For this purpose, the processes of solid self-pierce riveting, semitubular self-pierce riveting, friction element welding and resistance element welding are qualified for joining of the material combination mentioned by the adaptation of process parameters, the tools and the auxiliary joining parts. In addition, the UHSS+ sheet materials are modified with the help of local conditioning in such a way that the join ability is also given with conventional mechanical joining methods. The determined property profile of compounds from UHSS+ and the aluminum alloy EN AW-5182 shows that a reproducible connection quality can be achieved.
Prof. Dr.-Ing. G. Meschut , Sc. V. Sartisson