PVD coatings on aluminium substrates

It is well known that aluminium is today the most widely used metallic material besides steel. The mechanical characteristics of aluminium offer an increasing application field, especially where lightweight constructions are required. The demands for improved characteristics such as higher strength and greater durability are achieved by the development of new aluminium alloys. Continuous efforts are made in research into new possibilities for making use of the advantages of aluminium in applications that were reserved up to now for harder and more wear-resistant materials. Because of their environmental benefits modern PVD processes represent a better alternative to a number of conventional coating processes to deposit wear-resistant films on aluminium surfaces. The aim of this paper is to describe the possibilities of TiN coating on an aluminium alloy, A1MgSil, by application of the arcPVD process without damage to the heat-sensitive substrate material. Different machining and cleaning processes were used for the preparation of the aluminium substrates. The relationship between substrate pretreatment and coating characteristics is demonstrated. The influence of different process parameters such as etching, bias voltage and coating time as well as the arrangement of the substrates in the vacuum chamber were investigated. Multilayer (Ti and TiN) and graded coatings were deposited on the aluminium alloy to achieve the best results in deposition rate, microhardness and critical scratch load. To characterize the abrasive wear behaviour of the coated aluminium substrates a special sandblasting test was used. These results are also described in this paper. Finally a suitable process technology is provided for the application of thin protective films on aluminium in order to increase wear resistance.