Electrode wear in short-pulse resistance spot welding of aluminum AA 6016-T4
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RESEARCH PAPER
Electrode wear in short-pulse resistance spot welding of aluminum AA 6016-T4 Eric Schulz 1,2 & Ahmed Mahjoubi 1 & Matthias Wagner 1 & Holger Schubert 1 & Bharat Balasubramanian 2 & Luke N. Brewer 2 Received: 16 July 2020 / Accepted: 25 September 2020 # International Institute of Welding 2020
Abstract The influence of current pulse width on electrode wear during resistance spot welding of thin sheets (1 mm, 0.04 in) of aluminum alloy 6016-T4 was studied, and an increase in sheet surface roughness and electrode erosion was evident with increasing pulse time for the same weld nugget size. Aluminum alloy 6016-T4 is an especially critical material concerning electrode wear for resistance spot welding due to rapid onset of electrode sticking and erosion of the electrode surface. Typically, welding of this material therefore requires electrode redressing operations after approximately 20 to 30 welds to maintain constant weld size and sheet surface quality. It was demonstrated that a reduction of current pulse width is a means of reducing electrode wear without affecting joint properties. The electrode wear process involved a pickup of aluminum material from the sheets followed by alloying process, leading to formation of intermetallic phases and erosion of material from the surface of the electrodes with increasing number of welds made. A reduction of current pulse width positively affected electrode wear properties by reducing temperatures at the electrode and sheet surfaces, thereby delaying electrode wear and reducing its severity. Keywords Resistance spot welding . Aluminum welding . Automotive manufacturing technologies . Joining technologies . Electrode wear
1 Introduction Despite its application in high-volume automobile production for various alloys, the resistance spot welding (RSW) of aluminum has been limited by problems with rapid wear of the copper welding electrodes [1–4]. Aluminum alloys have high thermal conductivities, making it necessary to weld with high current levels. In addition, a naturally occurring oxide layer forms on the surface of the material, which is highly insulating and resistant to current flow. This leads to increased heating at the interfaces between electrodes and sheets during welding. Both of these factors promote a higher thermal load on the Recommended for publication by Commission III - Resistance Welding, Solid State Welding, and Allied Joining Process * Eric Schulz [email protected] 1
Mercedes-Benz AG, Sindelfingen, Germany
2
Center for Advanced Vehicle Technologies, The University of Alabama, Tuscaloosa, AL, USA
electrodes during welding and a more rapid degradation process [1]. In contrast to steel RSW, where redressing is typically required only after several hundred welds are made, aluminum RSW can result in much shorter electrode lives [5]. Furthermore, the wear mechanisms differ greatly. In steel RSW, the electrode face becomes enlarged as number of welds increases, known as the so-called “mushrooming effect”. As a result, the size of the contac
