For many years, RZ5 alloy has been the preferred material for helicopter transmission casings due to the combination of low density and good mechanical properties. More recently, however, the requirement for longer intervals between overhauls and hence improved corrosion properties has caused manufacturers to reconsider material choice.
In the past, RZ5 was generally used for gearbox casings but many new programmes will use WE43 instead including the main rotor gearbox castings. For this application, an aluminium transmission would have been used but for the exceptional corrosion resistance of WE43. The Eurocopter EC 120 and NH90 helicopters have also flown with WE43 transmission casings and WE43 is specified for the Sikorsky S92. Further applications for WE43 will go ahead in the future both on new programmes and also to replace RZ5 on older helicopters.
RZ5, ZRE1, MSR and EQ21 alloys are widely used for aircraft engine and gearbox casings. This will continue although it is likely that WE43 will be used increasingly for its corrosion and high temperature properties. Very large magnesium castings can be made, such as intermediate compressor casings for turbine engines. These include the Rolls Royce Tay casing in MSR, which weighs 130kg and the BMW Rolls Royce BR710 casing in RZ5. Other aerospace applications include auxiliary gearboxes (F16, Eurofighter 2000, Tornado) in MSR or RZ5, generator housings (A320 Airbus, Tornado and Concorde in MSR or EQ21) and canopies, generally in RZ5.
Magnesium alloy forgings are also used in aerospace applications including critical gearbox parts for the Westland Sea King helicopter and aircraft wheels, both in ZW3. Forged magnesium parts are also used in aero engine applications. In the future, magnesium forgings are most likely to be used in higher temperature applications