Corrosion Performance of Laser and Mash-Seam Welded Automotive Sheet Steels

The use of tailored-blanks is increasing in the automotive industry as manufacturers attempt to join dissimilar steel grades and thicknesses for parts consolidation and vehicle weight savings. Two methods, laser welding in a square-butt joint and resistance mash-seam welding of overlapped edges, have been used for select applications. Several automotive grade coated sheet steels were laser and mash-seam welded and evaluated for weld integrity, formability, and corrosion resistance. Salt spray and cyclic laboratory tests, and on-vehicle exposures were used for corrosion resistance evaluations. Regarding the corrosion performance of welded parts, it was observed that the weld area provided the weakest corrosion resistance on any given panel. The corrosion performance was, in part, a function of the width of the weld fusion zone. Additionally, the paint adhesion and the corrosion resistance of the welds were greatly influenced by surface oxidation and impurities within the fusion zone, variability of the joined coated substrate structure traversing the weld, and the extent of damaged coating in the heat affected zone as these items affected the subsequent phosphatability of the weld area.