Investigation on grain refinement by carbon addiction on AZ91D magnesium alloy

Grain refinement is an important practice to improve the properties of magnesium alloys. Although many grain refining methods have been developed for the Mg–Al alloy system, the addition of carbon containing agents to the melt, the so-called carbon addition method, offers many practical advantages because of the lower operating temperature and less fading. In this work 0.1% of carbon was added to a melt AZ91D magnesium alloy and the alloy was casted in a cylindrical mould. The cylinder was divided in three parts, which were underwent to two different heat treatments: solubilisation, solubilisation and aging. The samples microstructure was characterized by optical and scanning electron microscopy; mechanical properties were determined by Brinell hardness test and tensile strain test. The phases formed during solidification and heat treatments were investigated by SEM equipped with EDS and WDS analyzers. The carbon addiction was effective to refine the grain size of the alloy but its effect on hardness was negligible, so as the susceptivity to heat treatments.