A LIGHT-WEIGHT SOLUTION - INVESTMENT CASTING MAGNESIUM
17 May 2006 - Castings Technology International

The use of magnesium alloys has seen rapid growth over the last 10-15 years for high-pressure die cast automotive applications, and its properties are still being utilised to good effect in the sand cast form for aerospace and special applications.

The main reason for this success is the light weight of magnesium, two-thirds the density of aluminium. Furthermore, alloy developments have led to magnesium alloys with excellent corrosion resistance and, for some alloys, the elevated temperature performance is superior to many aluminium alloys.

In contrast, investment/precision cast magnesium is comparatively limited. The reason for this lies primarily with the potential reaction of magnesium with the ceramic mould material.

However, a research and development programme of work carried out at Castings Technology International has improved the knowledge of shell mould technology required for magnesium and has shown that by careful control of process parameters and use of effective purging techniques it is possible to produce excellent quality castings. Cti have demonstrated that by applying the knowledge now available, complex castings can be consistently produced to meet aerospace quality standards.

Suitable alloy selection for investment casting has proved to be important and two alloys are favoured, namely AZ91 and Elektron 21. AZ91 is suitable for simple shapes where properties are not a main concern. Elektron 21 is favoured when improved and consistent properties are required from room temperature up to around 200°C.

In conclusion, magnesium alloys can now be produced by the ceramic investment casting route and it is strongly recommended that design engineers communicate with Cti's casting engineers at the earliest stages of design.

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