Reliable alternatives to banned coatings
Now, new non-hexavalent chrome conversion coatings can be used very effectively with the IVD process
Acorn Surface Technology says effective environmentally acceptable surface treatments, such as IVD aluminium, can provide a reliable alternatives to cadmium and hexavalent chrome coatings.
Toxic and harmful metals such as cadmium and chromium have been very effective in protecting metal components from corrosion and wear, they have been used from the very early days of engineering, but today are increasingly banned from use. The search for acceptable replacements has been long and wide ranging, and many different solutions have been identified depending on the severity of the application.
Cadmium plating can be replaced by several different coatings but perhaps the most effective like-for-like coating is IVD aluminium. In this process pure aluminium is deposited in vacuum to give coatings 7.5 to 30 microns thick (similar to those used in cadmium plating). Since aluminium is chemically similar to cadmium and very close in the galvanic table it has similar protective properties. IVD gives similar salt spray corrosion resistance as cadmium but does not cause hydrogen embrittlement. IVD aluminium is also be used to prevent dissimilar metal or galvanic corrosion, such as when items made of stainless steel or titanium are used in contact with aluminium structures. In some areas IVD exceeds the properties of cadmium, for example it is stable up to 500 degrees C (cadmium is limited to 230 degrees C), it also exceeds cadmium in acid salt fog environments and can safely be used in contact with fuel - unlike cadmium.
One ecological negative about the IVD process has been the fact that the aluminium coating is usually passivated to enhance its properties using conventional chromate conversion coatings. These hexavalent chromates have been widely used in all manner of finishing applications from conversion coatings/passivate coatings, seal applications in anodizing, paint additives and many others. However, hexavalent chromates are toxic and their use is increasingly limited by legislation or banned altogether.
Now, new non-hexavalent chrome conversion coatings can be used very effectively with the IVD process. The IVD process can therefore be used to protect steels, high strength aluminium alloys and many other materials to the level previously achieved by cadmium plating - but with the added advantage of being totally environmentally acceptable.
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