Synergy of nano carbon black inoculation and high intensity ultrasonic processing in cast magnesium alloys

Commercial AZ series magnesium alloys containing three, six, and nine weight pct of aluminum (AZ31, AZ61 and AZ91) are investigated for their response to carbon black nano-particle inoculation and high intensity ultrasonic processing. Potency of inoculants is assessed under varying experimental conditions of untreated, carbon black treated and combined carbon black inoculation treatment followed by ultrasonic treatment conditions. Resulting grain refinement is studied and explained based on existing theories of nucleation and ultrasound induced phenomena in molten metals. It is observed that ultrasonic treatment helps to accelerate the wetting, de-agglomeration, and dispersion of inoculant particles, thereby resulting in refined microstructures. The hardness and tensile properties are evaluated and correlated with microstructural evolution during each of the processing approaches. The 0.2% proof stress, UTS, and total elongation to fracture values are superior for all the Mg alloys that were subjected to carbon black inoculation followed by ultrasonic treatment. This is ascribed to the grain refinement resulting from synergy of nano carbon black inoculation and high intensity ultrasonic processing.