Functionalising of a-C:H tool coatings and homogenization of the aluminum passive layer for the dry forming of aluminum

该项目旨在实现铝合金板材的干式成形，其基础是开发表面处理技术，以优化工具和金属板材的界面。在成形过程中，某些磨损机制导致刀具快速失效，阻碍了铝的干法成形的应用。这些机理可以用碳基刀具涂层的磨合行为来解释，并与铝板的自然钝化有关。非晶态氢化碳涂层(a-C：H)在与铝的干摩擦接触中表现出非常好的摩擦学性能。然而，磨合行为的特点是高粘着倾向和摩擦值。根据初步测试，磨合行为是一个单一的和暂时的阶段。在磨合阶段，a-C：H涂层将被功能化，从而降低附着力。作为该项目的一部分，将为a-C：H涂层的合成功能化开发表面处理。因此，通过对刀具表面进行等离子体抛光和对a-C：H涂层进行等离子体化学腐蚀，可以使涂层的粗糙度降低到几个纳米级，并消除a-C：H生长区。然后用闪光灯对a-C：H界面进行热石墨化处理。这些过程是高度特定于材料的。自然生成的氢氧化铝钝化层具有良好的摩擦学性能，将通过定向均匀调整板材表面的自然钝化层来合成。因此，现有的氧化层将被优选的伽马-AlOOH取代，以利用伽马-AlOOH在板材表面的减摩性能。合成的钝化层用合适的板材前处理取代了良好的水润滑。在形成过程中，氧化层将随着环境介质的变化而改变，以表现出摩擦和磨损优化的行为。随后可用于a-C：H工具涂层的功能化和铝钝化层的均质化的工艺将允许选择性地优化铝在成形过程中的结合机制。该项目建成后，这两种工艺的结合将能够实现铝合金的干法成形。

The project aims at the realization of dry sheet metal forming of aluminum alloys based on a development of surface treatments to optimize the boundary surfaces of tools and metal sheets. During forming processes, certain wear mechanisms cause a rapid tool failure and hinder the utilization of dry forming of aluminum. These mechanisms can be explained by the run-in behavior of carbon based tool coatings and are related to the native passivation of aluminum sheets. Both will be optimized in this project.Amorphous hydrogenated carbon coatings (a-C:H) show very good tribological properties in dry sliding contacts against aluminum. However, the run-in behavior is characterized by a high adhesion tendency and friction values. According to preliminary tests the run-in behavior is a singular and temporarily phase. During the run-in phase the a-C:H coating will be functionalized which leads to a lowered adhesion tendency. As part of this project, surface treatments will be developed for a synthetic functionalization of the a-C:H coating. Therefore, the roughness of the coating will be reduced to few nanometers and the a-C:H growth zone will be removed by plasma polishing of the tool surface and plasma chemical etching of the a-C:H coating. Afterwards the a-C:H boundary surface will be thermally graphitized by Flash Lamp Annealing. These processes are highly material specific. Hence, they will be separately optimized and subsequently combined to a surface treatment process.The natural generated aluminum hydroxide passive layer shows advantageous tribological properties and will be synthesized by a directed homogeneous adjustment of the native passivation layer on the sheet metal surface.Therefore, the existing oxide layer will be replaced by preferably gamma-AlOOH to utilize the anti-frictional properties of gamma-AlOOH within the sheet metal surface. The synthesized passivation layer substitutes the favorable water-lubrication by a well suited sheet metal pre-treatment. The oxide layer will be modified by changes in the environmental medium during formation in order to show friction- and wear-optimized behavior.The subsequently available processes for the functionalization of a-C:H tool coatings and homogenization of the aluminum passive layer will allow a selective optimization of the adhesion mechanisms of aluminum during forming operations. After completion of the project, a combination of both processes will enable the dry forming of aluminum alloys.