Grain Refinement of AZ91 Magnesium Alloy with a Novel Aluminum-Graphite Inoculant

Magnesium is a lightweight metal with a high strength-to-weight ratio, making it an ideal material for improving fuel efficiency. However, its poor mechanical properties necessitate the need for researchers to find ways of improving them for this material to find wider acceptance in industry. This study examines the grain refinement capabilities of an aluminum-carbon (graphite) composite in cast AZ91E magnesium alloy. With increasing carbon addition, ultimate tensile strength (UTS) and ductility improved, while yield strength (YS) remained largely unchanged. The fracture mechanism also remained unchanged with increasing carbon addition, showing mixed-mode fracture in samples of highest and lowest ductility. The nucleation mechanism was determined to be duplex nucleation of Al₄C₃ and Al₈Mn₅. X-ray diffraction analysis confirmed that the Al-C inoculant contained Al4C3 after sintering; however, most Al₄C₃ was formed in-situ during the melting and casting process.