Dry forming of aluminum alloys: from fundamental material and surface characterization to new tribological systems

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Within the general lightweight trends aluminum is in particular qualified for products of the automotive and aerospace sector as well as for mechanical engineering in general due to its weight advantage and excellent energy absorption capacity. However Aluminum alloys have high demands on the design of forming technologies. The strong adhesion tendency of aluminum alloys to common tool materials affect the component surface quality, the process stability and the targeted tolerances. A waiver of lubricants to avoid acquisition and disposal costs as well as to realize a sustainable production increases the tendency to adhesion significantly. Thus, the shortened tool life lowers the productivity and the attractiveness of weight-optimized aluminum components.This research project aims at the reduction of the adhesive wear of tools during dry forming of technically and industrially relevant aluminum alloys. The first phase of the project served for the identification and evaluation of basic adhesion mechanisms in sheet metal forming. Special focus was on the chemical composition of the sheet and tool surfaces. The significance of the oxide layer on the sheets as well as the elements in the tool coating became apparent. In terms of wear, anodized layers turned out to be better on pure aluminum; on 5xxx and 6xxx alloys it had a detrimental effect. Therefore, the native oxide layers that have arisen in oxygen-enriched atmosphere will be tested.Silver was particularly characterized by anti-adhesive qualities in the pure element regarding against aluminum alloys, but had an insufficient abrasion resistance. To develop a new tool coating in Phase II, silver should be embedded in a harder layer matrix without reducing its anti-adhesive qualities. In analogy to silver, silicon-doped, amorphous carbon coatings (a-C:H:Si) have an excellent friction and adhesive behavior, but an insufficient abrasive resistance. As a further approach to increase the abrasive resistance of a-C:H:Si-coatings multi-layer structures will be developed. For the qualification of the developed coating systems a basic tribological test stand and a strip drawing test are used. The efficiency of the coating systems will be finally demonstrated by application-based oriented deep drawing tests.In addition to the chemical compositions the resulting temperatures and contact normal stresses will be addressed in this project. The process windows in which dry forming can take place should be identified in the strip drawing tests. This process window should enable forecasts of the wear behavior in industrial processes.