![]() Where the higher rates of corrosion encountered under severe industrial and marine conditions must be prevented, a protective finish coating will be required.Ĭorrosion Rates of Zinc and Zinc Alloys in Various Atmospheres Material The corrosion rates shown in the table below for industrial environments may well be significantly higher than that which can now be expected in practice. The reduction in SO 2 levels in the atmosphere in Europe over recent years has brought about a marked reduction in the rate of corrosion of zinc surfaces in urban and many industrial environments. The table below shows the range of rates of corrosion that are likely to be encountered with zinc die castings the rate of corrosion is unlikely to exceed 12 microns/yr and may be as low as one-tenth of this. When exposed out-of-doors unprotected zinc alloy diecastings soon lose their bright metallic appearance and acquire a compact and closely adherent coating of corrosion products, which reduces the rate of subsequent attack. ![]() It has been reviewed in a monograph Zinc: ‘ Its Corrosion Resistance – reference 11‘ to which reference should be made for more detailed information than is contained here. ![]() The literature on the corrosion resistance of zinc in all its forms is very large indeed. This form of corrosion, which can lead to rapid failure, can only occur when harmful impurities, particularly tin and lead, exceed the specified levels in most countries reputable zinc die casters belong to schemes which guarantee the maintenance of strict analytical control on the alloy so that impurities never reach such levels. Diecast zinc alloy like other forms of zinc generally corrodes at an even, slow rate castings that meet the requirements of EN 12844 (and similar specifications in other parts of the world) are not subject to intercrystalline corrosion. Table 1 compares the rates of corrosion of high purity zinc and of zinc diecastings in a number of different environments. In most circumstances the behaviour of die cast zinc alloys are similar to that of unalloyed zinc and if in any application zinc or galvanized steel is known to be satisfactory, zinc die castings will usually also behave well the exception is in severe marine environments (see below). Zinc has excellent resistance to corrosion in most natural environments and this has given rise to its extensive use for corrosion protection. Corrosion Properties Corrosion Resistance
0 Comments
Leave a Reply. |