This crash-test gives an impressive demonstration of the interplay and effect of the aluminium-steel component; the aluminium absorbs the deformation energy while the steel maintains the desired clearance. Image: FroniusClick image to enlargeAs automotive manufacturers continue to shift towards lighter weight materials, they've refocused their attention on a breakthrough technology that allows welders to weld steel and aluminum. The hybrid material provides manufacturers with the strength of steel combined with the light weight of aluminum.

 The breakthrough technology emerged in the early 2000s, as a result of development efforts between Fronius International, a welding technology supplier, and Voestalpine AG, an Austrian steelmaker.Steel (left) and aluminium (right) are linked by a shared thermally-joined seam: the steel is brazed and the aluminium is welded. Image: FroniusClick image to enlarge

A recent Wall Street Journal artilce highlights the strides that have been made since then. The February 9, 2015 article notes that interest in the hybrid welded, lighter weight materials is rising among automotive OEMs, such as Ford and Honda Motor Co. The article notes that Audi and other customers are interested in the technology, if costs can be reduced.

According to Fronius, a viable technology to weld steel and aluminum first emerged in 2003 and since then the Fronius and Voestalpine have conducted trials and developed "high formability hybrid sheets."

The process to weld the two non-compatible materials continues to evolve. According to the Wall Street Journal article, the process is complex and expensive, two to three times as expensive as riveting and gluing techniques used on Vaoestalpine's shop floor.

In a news release about the technology, Fronius notes there are still "some technical boundary conditions" such as ensuring steel sheets are galvanized, that alumium sheets be made from materials of the AW5xxx or 6xxx series, and that AISi3Mn1 be used as the welding/brazing filler metal.

"The zinc layer on the steel sheet acts as a flux, wetting the steel. The crucial factor is the intermetallic phase (IMP). This should be as thin as possible, and no more than 10 µm. The strength of the joint is then so great that in tensile tests, the seam itself remains intact and the break takes place in the aluminium sheet. Since then, multi-year tests on shaped hybrid sheets have proved that neither intercrystalline nor stress or crevice corrosion occur; only minor surface corrosion has been detected. The ideal welding systems for the hybrid sheets have proved to be ones that use the CMT process to vertically braze-weld both sides ‘in sync’ from top to bottom. The know-how from Voestalpine relates to weld-preparation in terms of the seam-geometry, while the patented filler metal and the modifications to the CMT system are the fruits of Fronius’ R&D effort.

The Wall Street Journal article describes how Voestalpine welder Alois Leitner welded two car parts, one zinc coated and one aluminum. "What resulted was a part so coheisve it can be stamped as if it were one could exchange today's laser welded steel parts with steel-aluminum parts," notes Wolfgan Eder, chief executive of Voestalpine, who is quoted in the story.



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