Prize-winning hybrid sheet revolutionises automobile industry

Developed jointly by Fronius and voestalpine, the steel-aluminium sheet was awarded the Innovation Prize by the specialist magazine Autorevue on October 20th in the Casino Baden. An award for welded-brazed joints in lightweight automobile construction, joints that have previously been unthinkable.

The hybrid sheet is the result of intensive research. It took fifteen years of basic research to create the steel-aluminium joining process. Researchers from both companies spent another five years developing a semi-finished product that could be used in the field. Transforming this product into fully operational parts has opened up completely new possibilities in the automobile industry.

The challenging aspect of this joint was that an intermetallic phase (IMP) takes place when welding steel with aluminium. If this is more than 10μm thick, the joint is not stable, meaning that it is brittle and breaks straightaway. The aim was therefore to achieve a thickness of less than 5μm. The high corrosion susceptibility of this joint and the different thermal expansion of steel and aluminium were also factors.

The CMT (Cold Metal Transfer) process, in which the weld seam is subjected to very little heat, provided a possible solution to the problem, as the resulting IMP content is low and the formation of mixed phases and thermal distortion is reduced. The researchers finally made a breakthrough. They used CMT as a welding and brazing process and produced the best joint by welding the aluminium side and brazing the steel side.

This revolution in joining technology makes it possible to use a trusted semi-finished product in completely new material combinations. Crash tests prove that the weld seam holds and that the hybrid sheet satisfies all requirements. Application areas are predominantly roof bows and longitudinal members for the automobile industry.

On October 20th, Klaus Fronius and voestalpine representatives received the trophy for this cutting-edge research and joined the list of winners, which includes BMW and Mercedes Benz.

Statement by Klaus Fronius

The 9th Autorevue Award asked readers to choose their favourite new automobiles of the year in the following categories: small & compact cars, saloons & estate cars, off-road vehicles, vans, convertibles, sports cars and alternative cars. The editors also presented the aforementioned Innovation Prize.