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，由于铝的重量优势和出色的能量吸收能力，它特别适合汽车和航空航天部门以及机械工程的产品。然而，铝合金对成形工艺的设计要求很高。铝合金对常用刀具材料的强附着力影响了零件的表面质量、工艺稳定性和目标公差。为了避免购买和处理成本以及实现可持续生产而放弃润滑油，这大大增加了粘附的趋势。因此，缩短的刀具寿命降低了生产率和重量优化铝部件的吸引力。本研究项目旨在减少技术上和工业上相关的铝合金干成型过程中工具的粘着磨损。该项目的第一阶段用于识别和评价金属板成形中的基本粘附机制。特别关注的是板材和工具表面的化学成分。氧化层在板材上的重要性以及在工具涂层中的元素变得明显。在磨损方面，阳极氧化层在纯铝上表现得更好；对5xxx和6xxx合金有不利影响。因此，将对富氧大气中产生的天然氧化层进行测试。在纯元素中，银对铝合金具有抗粘接的特性，但耐磨性不足。为了在第二阶段开发一种新的刀具涂层，银应该嵌入更硬的层基质中，而不降低其抗粘接性能。与银类似，掺杂硅的非晶碳涂层（a-C:H:Si）具有优异的摩擦和粘合性能，但耐磨性不足。作为进一步提高a- c:H: si涂层耐磨性的途径，多层结构将得到发展。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带材拉伸试验。涂层系统的效率最终将通过基于应用的定向拉深试验来证明。除了化学成分外，所产生的温度和接触正应力也将在这个项目中得到解决。应在带材拉伸试验中确定可进行干成形的工艺窗口。这个过程窗口应该能够预测工业过程中的磨损行为。

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.