The suitability of various brazing materials for the manufacture of steel-aluminium mixed joints is investigated using the example of the CMT (cold metal transfer) process. The properties of the joints are compared with each other on different sheet thickness combinations. The experimental results reveal that low-heat GMA processes are very suitable for the manufacture of the mixed joints. With zinc-based brazing materials, it was possible to achieve the same strengths as those of the base materials particularly in the sheet thickness range up to 1 mm. The ZnAl15 brazing material exhibited better processing properties and joint strengths than ZnAl4. Due to its reversing wire movement, the CMT process favoured the transfer of the droplets in the case of the zinc-based brazing materials with only low thermal loadability. For the sufficient wetting, it was necessary to deposit a higher wire quantity than with aluminium-based brazing materials. The best joint strengths were achieved in the case of zinc-based brazing materials with a zero gap. Small gap dimensions proved to be favourable with aluminium-based brazing materials. The zinc coat constituted the prerequisite for good wetting of the steel sheet. It was possible to achieve approximately identical results on coatings customary in automobile construction. However, in order to avoid any possible wetting defects, preference should be given to thicker zinc coats. The use of aluminium-based brazing materials resulted in continuous intermetallic layers (Fe2Al5 and FeAl5) with maximum thicknesses between 2 and 5 micrometer. In the case of zinc-based brazing materials, an extremely distinct growth of intermetallic phases with local thicknesses up to 35 micrometer occurred in regions of the highest energy input. Recommendations are given in order to achieve optimum joint properties.
Joining of steel-aluminium mixed joints with energy-reduced GMA processes and filler materials on an aluminium and zinc basis
Welding and Cutting ; 7 , 1 ; 30-38
2008
9 Seiten, 22 Bilder, 1 Tabelle, 18 Quellen
Aufsatz (Zeitschrift)
Englisch
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