Improvement of mechanical and corrosion behaviour in die casting magnesium alloys with the addition of grain refiners.

This paper shows a work carried out to obtain better properties in magnesium alloys used on high pressure die casting process (predominantly AM60B and AZ91D). This study starts with the selection of grain refiner materials to be employed for these alloys. Simple elements such as Mn, Ti, C, Si⋯ and compound elements as ZnO, TiB₂ were selected as promising grain refiners. Tensile strength and elongation were chosen as main mechanical properties to be tested employing a design of experiments and laboratory tests. The determination of the fading effect of the grain refiner on the magnesium melt bath is also discussed. This work shows also the results obtained after the addition of selected grain refiners on corrosion resistance, by a new corrosion evaluating method based on affected surface area instead of weight loosing. Finally the best refiner elements for the analysed alloys are assessed, determining their concentration and dissolving time to obtain the best mechanical and corrosion properties. Tensile strength increases up to 6% for AZ91D alloy and up to 12% for AM60B alloy, elongation is also increased and corrosion resistance is even improved in both alloys.