Improvement of the resistance spot welding of Al-Mg-Si alloys by using cladding technology: An optical and mechanical characterization study

The recent body in white developments within lightweight structural automotive applications has experienced an increasing demand on the joining of aluminum (Al) alloys. However, new challenges come along with it. For example, the resistance spot welding (RSW) process is currently limited, regarding the suitable aluminum alloys for structural applications. Some alloys present poor mechanical performance, despite good electric and chemical properties (i.e. AW-1000, 3000 and 4000 series), while others, especially the heat treatable Al-Mg-Si alloys (6000 series), may present process robustness issues, narrow welding lobe and/or short electrode life, despite good mechanical properties. The cladding of different aluminum alloys is currently launched from some aluminum producing companies and possess the potential to improve the sheet weldability, whilst maintaining the structural performance. The approach is based on the combination of a high conductive, electric stable aluminum alloy as covering sheet, with a high strength alloy as core sheet. The objectives of this work are the evaluation of an improved weldability of an AW-6111 (core sheet) cladded with an AW-4040 (cover sheet), by establishing a proper welding lobe (estimated by means of the nominal and maximum welding current levels and weld spot diameters), an analysis of the electrode erosion behavior and a characterization of the formed microstructure. Comparisons with a pure AW-6111 aluminum sheet are done. The results have shown that the cladded sheets presented improved weldability characteristics and increased the electrode service life.