The majority of automotive body shop welding consists of resistance spot welding (RSW) steel sheet due to its inherently low cost and high speed. With the introduction of aluminum, it is desirable to continue using RSW as the joining process. However, the presence of insulating oxide layers on the aluminum alloy material surface presents significant problems in obtaining consistent spot welding processes. This problem has been solved by General Motors (GM) with the invention of its patented Multi-Ring Domed (MRD) electrode (Refs. 1,2). This key process is currently used by the company in automotive structures, such as for the 2014 Corvette Stingray see lead photos. The electrode design incorporates several protruding concentric rings on the weld face that act to deform the aluminum sheet surface on contact and break through oxides on the surface, which is essential to obtaining a stable aluminum spot welding process. Developing dressing blades that cut protruding rings into the electrode weld face has been a critical enabler for its introduction into GM plants. The conclusions are: 1. Wear mechanisms for GM's MRD electrode were elucidated for RSW aluminum sheet Alloys AA5754-O and AA6111-T4. Analyses consisted of visual examination, peak height measurements, and SEM examination. 2. Based on the findings in this study, MRD electrode wear appears to occur in several steps that begin with deformation of the small concentric rings against the aluminum sheet surface. Once rings are significantly flattened, reaction accelerates between the copper electrode and aluminum sheet rapidly forming an aluminum contamination layer. Finally, as the layer thickens, it cracks and spalls under the mechanical and thermal stresses experienced during spot welding. 3. For welding Alloy AA6111-T4, electrode wear occurred primarily by ring deformation followed with eventual pit formation. This was attributed to the higher hardness of AA6111-T4 relative to annealed AA5754-O. The AA6111-T4 sheet responded best to the high-hardness, high-conductivity electrode C15760, which would limit ring deformation without the generation of excessive heat at the electrode/sheet interface. 4. For welding Alloy AA5754-O, ring deformation was less pronounced, most likely due to the lower hardness of the sheet; however, pitting became the primary wear mechanism. This was attributed to higher electrode/sheet interface temperatures most likely caused by the Mg-containing oxides inherent on Alloys 5XXX, Al-Mg. No electrode material was preferred for welding AA5754-O aluminum.


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    Title :

    Improving aluminum resistance spot welding in automotive structures


    Contributors:

    Published in:

    Publication date :

    2013


    Size :

    9 Seiten, 8 Bilder, 5 Tabellen, 6 Quellen



    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English




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