SOME SURFACE FACTORS THAT AFFECT THE SPOT-WELDING OF ALUMINUM

The resistance spot weldability ofAA5754 (Al. 3.0 Mg) has been rested with three characteristic surface conditions, etched, mill finish and pretreated/lubricated sheet combined with the presence of a structural adhesive (weld bonding). Each surface type is of potential interest f or high volume automotive vehicle production. The results were compare d with contact resistance measurements made to the German standard DVS 2929 which suggest that neither mill finish nor pretreated/lubricated surfaces with adhesive present, should be weldable. However, it was f ound that all three surface conditions were readily weldable, producin g more than 1000 welds when suitable equipment (Medium Frequency DC) a nd appropriate welding parameters were used. Etched surfaces gave the most consistent spot weld strengths but acceptable spot welds were als o obtained from the mill finish and pretreated/lubricated surface. Of the three surfaces tested, only the pretreated and lubricated surface is known to also of offer acceptable structural bond strength durabili ty in weld bonding applications.