Aluminum and its alloy relatives are marching ahead at full speed as an alternative construction material in a variety of areas of industrial application. They offer low material density, making them an especially appealing option for engineers working in the automotive sector, the aerospace industry, shipbuilding, and trains. Aluminum sheets with the required material thickness can be rolled into pipes before welding lengthways. This is particularly important in industrial applications involving tubular components or profiled parts. Until now, producing larger sections of materials has not been financially viable, because the only possible conventional method was to use multiplepass welding. Not only is this time-intensive, it is also expensive. One alternative has been to use electroslag welding or submerged arc processes. The Steinbeis Innovation Center for Intelligent Functional Materials, Welding and Joining Techniques, Implementation has been investigating this process and has successfully developed a new process along with a welding powder that are now capable of achieving the required performance when joining larger aluminum cross sections.
With submerged arc welding, the electric arc burns inside a gas cavern underneath a layer of welding powder. As the parts are welded, the powder melts and develops into a liquid called welding slag. This moves around on the weld metal, shapes it, and protects it from oxidation. This technique offers a variety of benefits compared to other electric arc welding processes. For example, the high electrical current needed when using thick wires (> 3mm) is excellent for the rate of deposition and this makes it possible to achieve large seal volumes economically. Thick aluminum parts can be used in a large number of areas such as toll frames (mounted over highways), shipbuilding components for high-speed vessels, aluminum car wheel rims, or components required for large engines. As a result, there was strong demand for an effective submerged welding process and a suitable welding powder to go with it. The experts decided they needed to move forward with aluminum submerged welding and develop it into an economically viable joining process that would enjoy widespread acceptance in industry.
Working in collaboration with an industrial consulting firm called Bavaria Schweistechnik GmbH, the experts at the Steinbeis Innovation Center for Intelligent Functional Materials, Welding and Joining Techniques, Implementation have now developed an innovative welding powder as well as a suitable submerged welding technique for use with thick sheets of aluminum. At the start of the project, the experts experimented with and optimized the chemical composition of the new welding powder. They focused on technical processes to improve the quality of the seal. The main job of welding powder is to remove aluminum oxide layers during the welding process and prevent pores or cavities from forming. It also helps avoid poor joins along the welding seam. To this end, the Steinbeis experts developed a variety of powder mixtures focusing on the chemical composition and the ratios of various ingredients. Following a series of welding tests, they successfully identified the influence of different ingredients within the powder and their impact on arc ignition and arc properties. They also examined seal formation and slagging. “One thing we noticed with the samples we welded using the different powder mixtures – which were mainly composed of oxides – was that the welding process was relatively stable and the seals were good,” explains Dr.-Ing. Khaled Alaluss, who is co-director of the Steinbeis Center in Dresden. The welding slag this produces keeps the welding process stable and it is easy to detach and remove. To improve the chemical composition of the powders, the two teams working on the project examined significant influences on the materials. Based on this they succeeded in using the new powder mixtures to produce aluminum welding joins of the required quality – with no pores and no problems with the joins. Finally, the welding experts developed a corresponding welding system to produce submerged arc welds on aluminum and aluminum alloys (AlMg4.5Mn). The quality of welding results depends on:
To conclude their project, the experts considered the specific conditions encountered in industrial welding and made an evaluation of the new submerged arc welding technology. They did this by producing aluminum demonstration parts, in this case with a high quality joined connection (linear join, v-shape join, twin v-shape join), which they then examined in detail for technical properties and performance.
The project was completed successfully and the experts at both Steinbeis and Bavaria Schweistechnik were satisfied that they had proved that the seals they had produced delivered the required component quality in terms of strength, porosity, the welding root, and hardness/structural texture. “So we showed that the properties this produced with the welded aluminum joins, both in mechanical and technological terms, depends entirely on the main process parameters,” says Prof. Dr.-Ing. Gunnar Burkner, summarizing the result of the project. The strength of the welded joint was 75% of the minimum value of the base material (AlMg4.5Mn), another confirmation of the quality of the seal.
Dr.-Ing. Khaled Alaluss and Prof. Dr.-Ing. Gunnar Bürkner head up the Dresden-based Steinbeis Innovation Center for Intelligent Functional Materials, Welding and Joining Techniques, Implementation, which primarily works in the fields of applied research and development, design, and the application of components and materials. Oleg Nuss is an assistant at the center and also a member of the project team that worked on the development of the welding process. Hubert Lettner is the managing director of Bavaria Schweißtechnik GmbH, a welding firm based in Unterschleissheim (north of Munich) that specializes in powders, wires, and ligaments.
Dr.-Ing. Khaled Alaluss, Prof. Dr.-Ing. Gunnar Burkner, Oleg Nuss
Steinbeis Innovation Center Intelligent Functional Materials, Welding and
Joining Techniques, Implementation (Dresden)