Anzeige der Artikel nach Schlagwörtern: chrome
Chromium is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. While chromium metal and Cr(III) ions are not considered toxic, hexavalent chromium, Cr(VI), is both toxic and carcinogenic. 85 % of the available chromium is used in metal alloys. The remainder is used in the chemical, refractory, and foundry industries. Chromium compounds are used in leather products, dyes, paints, cement, mortar and are anti-corrosives. Chromium salts (chromates) are allergic to some people. Chrome ulcers are often found in workers that have been exposed to strong chromate solutions in electroplating, tanning and chrome-producing manufacturers [1, 2]
Nowadays most aeronautical parts made of aluminium alloys are protected against corrosion by surface anodising and multilayer painting. The treatment is usually carried out with Cr(VI) based compounds. However Cr(VI) substances are affected by REACh regulation and the European Commission will set more and more restriction for their use from 2024 onwards. To date, there is not any Cr(VI)-free protecting treatment for Aluminium 7000 series alloys that match the results obtained with the Cr(VI) based coatings, so, it is necessary to develop an environmentally and Cr(VI)-free acceptable alternative process.
There is a growing demand for light metal alloys components in aerospace and automobile fields primarily to save fuel cost. Magnesium alloys promise a great potential for various applications as lightweight structural materials. This advantage stems from their low densities and high specific strength/weight ratio. Other advantages are good electrical and thermal conductivity, good impact strength, ability to dampen shockwaves, ease of forming at room temperature, weldability, buckling resistances, ductility and pressure tightness. Despite sounding like a designers' dream metal, magnesium has two grave drawbacks that limit their widespread applications: poor corrosion resistance and relatively frail surface mechanical properties. Owing to the exceptional engineering properties of magnesium alloys ample attempts have been made in the last few decades to develop suitable surface protection techniques. In this article the advances of chemical conversion coatings on the magnesium alloys are discussed.