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

在一般的轻量化趋势中，铝因其重量优势和出色的能量吸收能力而特别适合汽车和航空航天部门的产品以及一般的机械工程产品。然而，铝合金对成形工艺设计提出了很高的要求。铝合金对常用刀具材料的强烈粘结影响了零件的表面质量、工艺稳定性和目标公差。为避免购置和处置费用以及实现可持续生产而放弃润滑剂，会大大增加粘附性。因此，刀具寿命的缩短降低了重量优化铝件的生产率和吸引力。本研究项目旨在减少技术和工业相关铝合金干成形过程中刀具的粘着磨损。该项目的第一阶段用于确定和评价板材成形中的基本粘结机制。特别关注了板材和工具表面的化学成分。板材上的氧化层以及工具涂层中的元素的重要性变得明显。在耐磨性方面，纯铝的阳极氧化层效果较好，而5xxx和6xxx合金的耐磨性较差。因此，将对在富氧气氛中产生的自然氧化层进行测试。纯元素中的银尤其具有与铝合金的抗粘附性，但耐磨性不足。为了在第二阶段开发新的工具涂层，应该在不降低其抗粘附性的情况下将银嵌入更坚硬的层基质中。与银、硅掺杂、非晶态碳涂层(a-C：H：Si)类似，a-C：H：Si涂层具有良好的摩擦和结合性能，但耐磨性不足。作为提高a-C：H：Si涂层耐磨性的进一步途径，多层结构将被开发出来。为了对所开发的涂层系统进行鉴定，使用了基本的摩擦学试验台和拉拔试验。涂层系统的效率最终将通过基于应用的深冲试验来验证。除了化学成分之外，本项目还将讨论由此产生的温度和接触法向应力。在带材拉拔试验中，应确定可进行干成形的工艺窗口。该工艺窗口应该能够预测工业工艺中的磨损行为。

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.