Applications of Magnesium Alloys
Introduction to Magnesium alloy applications
Magnesium alloy developments have traditionally been driven by aerospace industry requirements for lightweight materials to operate under increasingly demanding conditions. Magnesium alloys have always been attractive to designers due to their low density, only two thirds that of aluminium. This has been a major factor in the widespread use of magnesium alloy castings and wrought products.
A further requirement in recent years has been for superior corrosion performance and dramatic improvements have been demonstrated for new magnesium alloys. Improvements in mechanical properties and corrosion resistance have led to greater interest in magnesium alloys for aerospace and speciality applications, and alloys are now being specified on programmes such as the McDonnell Douglas MD 500 helicopter.
Magnesium alloys in Aerospace
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.
Why is Magnesium used for the Manufacturing of Automotive Parts?
The permanent reduction in vehicle weight is one of the major means available to improve automotive fuel efficiency. High-strength steels, aluminum (Al), and polymers are already being used to reduce weight significantly, yet, further substantial weight reductions could be achieved by the more frequent use of magnesium (Mg) and its alloys. Magnesium alloys are currently used in relatively small quantities for auto parts, mostly limited to die castings, e.g., housings as outlined in more detail below.
For conventional passenger vehicles nearly 90% of their total life time energy consumption used from the time of production to the time of disuse or scraping is consumed by carrying their own weight and persons around. Hence, weight reduction is among the biggest key challenges for increasing automotive fuel efficiency.
Magnesium alloys in Automotive Engineering and Motor Racing
The use of magnesium alloys in automotive manufacturing shows promise, with most applied research efforts currently placed on the applicability to auto applications which carry relatively low mechanical loads.
In spite of an apparent cost penalty, partiularly magnesium castings are currently used in a number of automotive body, chassis and powertrain. More specific, the metal is predominantly used in die-cast parts including four-wheel-drive transfer cases, transmission cases, engine cradles, steering-wheel components, seats, and instrument panels. While magnesium is abundant and is about a quarter of the weight of steel and two-thirds the weight of aluminum, it can present processing problems.
In motor racing, RZ5 is generally used for gearbox casings although MSR/EQ21 alloys are also being used increasingly due to their superior ambient temperature properties or because of increased operating temperatures. RZ5 wheels have been shown to have significantly better performance than Mg-Al-Zn alloy wheels under arduous racing conditions. Due to the high operating temperature of racing engines, WE54 castings have been used for a variety of Formula 1 engine parts and are used for engine components for a limited edition road car. Forged WE54 pistons offer great future potential for motor racing and other applications will exist for other wrought products.
Magnesium alloys are also used in many other engineering applications where having light weight is a significant advantage. Magnesium-zirconium alloys tend to be used in relatively low volume applications where they are processed by sand or investment casting, or wrought products by extrusion or forging. Zirconium-free alloys, principally AZ91 but also other alloys, are used in automotive and various other high volume applications.