Effect of Foundry Processing on the Corrosion Performance of High Purity Magnesium Sand Casting Alloys

Magnesium sand casting alloys are available to users who require excellent mechanical properties and high corrosion resistance with light weight. The corrosion behaviour of these alloys, in particular high purity alloys, depends on foundry processing during casting manufacture and subsequent treatments. Whilst high purity alloys such as Elektron WE43, WE54 and AZ91E will achieve corrosion rates similar to aluminium based alloys, processing factors can influence the corrosion resistance of the finished part. Molten metal handling prior to casting plays a major role in the level of undesirable species such as iron containing zirconium particles, cathodic metal impurities and flux when a fluxed technique is used. The effect of metal handling on the level of the aforementioned contaminants is discussed. The benefits of corrosion resistance achieved in “high purity” alloys can be negated by contamination of cast part surface through media blasting/brushing by unsuitable material. The effect of such contamination has been investigated and practical methods to minimise it are described.