Properties of Magnesium Plaster Castings

The demand for magnesium prototypes is growing very rapidly with the increasing number of new applications for magnesium die castings. Plaster mold casting is becoming more used amongst all other prototyping methods because it can produce castings with thin walls, smooth surface finish and close dimensional tolerances. However plaster mold casting of magnesium alloys has only been used until now by a few foundries because of the risks of violent reaction if the process is not carefully controlled. For this reason, very little quantitative information about properties of plaster cast magnesium alloys is available in the literature.

In this study, mechanical, corrosion resistance and microstructural properties of alloy AZ91E are reported as a first phase of the work being conducted at the Institute. As cast (F), solution annealed (T4) and solution annealed and aged (T6) properties of 12,5 mm (1/2 inch) diameter test bars were studied. The influence of chilling, grain refining and combination of both was investigated. Comparative data on corrosion resistance of plaster cast and sand cast plates are also reported.

The experimental results show that:

• Chilling and grain refining significantly improve the mechanical properties of plaster cast AZ91E alloy.
• Solution annealing and ageing heat treatment further increases the mechanical properties of plaster cast AZ91E.
• The corrosion rate measured in preliminary tests for plaster cast AZ91E is lower than that of sand cast AZ91E.