T.J. Chen

Semisolid Microstructure of AZ91D Magnesium Alloy Refined by MgCO3

AbstractThe microstructural evolution of an AZ91D alloy refined using 1% MgCO3 is investigated during partial remelting at 580C (1076F). Simultaneously, the effect of the initial as-cast microstructure on the semisolid microstructure and the microstructure uniformity of semisolid rods are discussed. The results indicate that the microstructural evolution includes four stages: the initial coarseningstructure separationspheroidizationfinal coarsening The finer the as-cast microstructure, the smaller and more spheroidal the primary particles are in the semisolid microstructure. For alloys with a grain size of 50–100μm, the resulting primary particle size is slightly larger than the initial grain size. But for the alloys having larger size grains (>150μm), the result is just the opposite. The main reason which leads to this difference is the different evolution mechanisms determined by the as-cast microstructure. To obtain a semisolid ingot with uniform microstructure, an ingot with uniform as-cast microstructure must be used.