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To capitalise on the strengthening potential of zirconium as a potent grain re® ner for magnesium alloys, the mechanisms of adding zirconium to magnesium and its subsequent grain re® ning action need to be understood. Using a Mg ± 33 . 3Zr master alloy (Zirmax supplied by Magnesium Elektron Ltd) as a zirconium alloying additive, the in¯uence of different alloying conditions on the dissolution of zirconium in magnesium was investigated. It was found that owing to the highly alloyable microstructure of Zirmax, the dissolution of zirconium was generally complete within a few minutes in the temperature range 730 to 780°C. Prolonging and/or intensifying stirring were found to have no conspicuous in¯uence on further enhancing the dissolution of zirconium. In all cases studied, the average grain size increased with increasing holding time at temperature while the total zirconium content decreased. The ® nest grain structure and highest total zirconium content corresponded to sampling immediately after stirring. Pick up of iron by molten magnesium from the mild steel crucibles used for melting and holding, was signi® cantly delayed or avoided in the temperature range 730 to 780°C by coating the crucibles with boron nitride. It is therefore feasible to conduct zirconium alloying at 730°C without the need of a considerable excess of Zirmax addition using a properly coated or lined steel crucible.MST/5360

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