Papers by Keyword: Carbon Inoculation

Abstract: The Mg-3% Al melt was treated by carbon inoculation and Mn addition. The effects of Mn addition and addition sequence on the grain refinement were investigated. The effect of Mn on the grain refinement of Mg-3 %Al alloy by carbon inoculation was closely associated with the operating sequence of carbon inoculation and Mn addition.Mn has no obvious effect on the grain refinement under the condition that Mn pre-existed in the Mg-Al melt before carbon inoculation. However, Mn played an inhibiting role under the condition that the Mg-Al melt had been inoculated by carbon before Mn addition. The Al4C3 particles should act as potent nucleating substrates for Mg grains in the sample treated by carbon inoculation. However, the Al-C-Mn particles with Al4C3 coating film could be observed in the sample treated by Mn addition and then carbon inoculation. These particles with duplex phase structure should also act as potent nucleating substrates for Mg grains, resulting in grain refinement. The nucleating potency of most Al4C3 particles was possibly poisoned by the formation of Al-Mn-rich coating film or the Al-C-Mn intermetallic compound, resulting in grain coarsening in the samples treated by carbon inoculation before Mn addition.

Abstract: The Mg-3% Al melt was treated by carbon inoculation and Fe addition. The influence of Fe on the formation of nucleation was investigated. That Fe inhibited the grain refinement of the carbon-inoculated Mg-3%Al alloy or not was closely associated with the operating sequence of carbon inoculation and Fe addition. Under the condition of Fe addition firstly and then carbon inoculation, the Al₄C₃ particles and the particles with duplex phase structure of Al₄C₃ coated on Al-C-Fe or Al-Fe could be observed. Both kinds of particles should act as nucleating substrates for a-Mg grains, resulting in no obvious effect of Fe on refining efficiency of carbon inoculation. Under the contrary condition, the potency of Al₄C₃ nucleating substrates was poisoned by transforming Al₄C₃ into Al-C-Fe-rich intermetallic particles, resulting in grain-coarsening.

Abstract: A homogeneous microstructure of as-cast magnesium alloys is necessary to improve the formability during their subsequent thermomechanical processing. In Al-containing magnesium alloys, the grain refinement by carbon inoculation is considered to be the best approach until now. However, the mechanism of grain refinement is unclear. The present work investigates the coring microstructure in Mg-Al alloys inoculated with carbon using FIB, SEM and TEM techniques. In each grain one or more “hillocks” exist, enriched with carbon, manganese and aluminium. This is possibly related to the inhomogeneous nucleation of alpha-magnesium. The precipitates in these “hillocks” are always surrounded by the aluminium-rich zones. These characteristics of microstructure observed in Mg-Al alloys with carbon inoculation are compared with that observed in Al-free magnesium alloys inoculated by zirconium. The similarities between them are discussed. A novel mechanism is suggested to explain the grain refinement in Mg-Al alloys inoculated by carbon.