Corrosion Resistant Magnesium Alloys

Cast magnesium alloys have been used extensively in heli copter transmission housings for many years. Older alloys, such as AZ91C, have been gradually replaced by ZE41A over the last 20 years. AII these long established alloys, however, are susceptible to corrosion attack particularly in marine and other aggressive environments. As a result, throughout the aerospace indvstry, there has been a gradual decline in the use of magnesium alloys in recent years. This paper presents data on two recently developed alloys both of which have an intrinsic corrosion resistance similar to that of aluminium base casting alloys. AZ91E, a high purity version of the old AZ91C alloy, is suitable for prolonged use at temperatures up to 240°F. WE43 is a high strength alloy with long term stability up to 480°F. To supplement their intrinsic corrosion resistance, outstanding surface protection schemes have been developed and are described. On-going development work on RST magnesium alloys is outlined showing that magnesium based alloy materials with even greater corrosion resistance may be available in future years.