Influence of lubricants on electrode life in resistance spot welding of aluminum alloys

Rapid electrode tip degradation and inconsistent joint strength are two major problems associated with resistance spot welding of aluminum alloys. A new approach of lubricating the contact between electrode and aluminum sheet to influence and perhaps extend the electrode life was examined. Different metal-working lubricants were placed between the electrode and aluminum sheet to produce different surface conditions. Keeping all weld conditions constant, electrode life experiments were conducted for both lubricated and unlubricated conditions. Joint shear strength values were periodically measured as hundreds of welds were made until either explosion/sticking occurred or a drop in the shear strength indicated the end of the effective electrode tip life. For the same welding conditions and failure criteria, one "good" lubricant was found to extend the electrode life to almost double that of the unlubricated surface (as received). A second set of experiments was performed to examine the action of the good lubricant. These experiments involved a variety of smaller studies including scanning electron microscopy, x-ray diffraction, hardness measurements, and electrical resistance measurements. The results of this second set of experiments suggested that the good lubricant thinned the surface oxide layer, thus reducing the heat generation at the electrode-worksheet interface. This lower heat generation reduced alloying and pitting rate, thus increasing electrode tip life. Future work on improving the good lubricant was contemplated.