Over the years, research on trivalent chromium passivation (TCP) has expanded into many fields of application, among them as a replacement for conversion coatings containing hexavalent chromium (Cr6), known as chromates. REACHcompliant TCP processes have been found to be adequate replacements for chromates, however, implementing them in the highly safety-minded aviation industry, for example, requires fundamental knowledge about the layer composition of these types of conversion coatings. This article outlines the formation of layers in trivalent chromium (Cr3) passivation over the copper-containing aluminum alloy EN-AW 2024.
For post treating anodising layers on aluminium, typically two different technologies are applied, the hot water sealing at 96-100 °C and the cold sealing using reactive salts to plug the pores of the anodic coating. Both applications show major disadvantages. Whereas the hot water sealing is extremely energy consuming due to the mandatory hot process temperature, the low temperature sealing processes typically apply nickel compounds being harmful to the environment. Nickel salts are toxic and carcinogenetic, having irreversible effects on the human body and health. Furthermore, nickel containing waste waters are difficult to treat, especially when also aluminium is present . New nickel-free technologies have been developed accordingly, enabling a low temperature application yielding in major energy savings. The deposition of antisoluble compounds in the pores of the anodizing layer leads to best stability and corrosion protection, exceeding the performance of hot water sealing. The new process solutions as being non-toxic are less risky to store and to handle, assisting the safety at work. Implementing a new photometrical method for analysing the ingredients, process stability and production quality can be improved . In some cases, the pH-resistance of the anodised surface can be enhanced, extending the application field of anodised aluminium. Moreover, the waste water treatment of the rinses is carried out at pH 9–10, hence, can be done mutually with aluminium containing effluents.
What should users take into account when planning a new cleaning system and choosing a suitable process? Many different parameters need to be considered. A variety of different aqueous cleaning processes is available and these processes can be adapted to meet individual requirements.了解更多
Trivalent chrome processes are the ideal alternative to hexavalent chrome plating and produce coatings of a similar colour. The specialist finishing company Oberflächentechnik Döbeln has been using trivalent chrome successfully for more than a year.了解更多