Strips of magnesium alloy AZ31-B were cast on a simulator of a horizontal single belt caster incorporating a moving mold system. Mixtures of CO2 and sulfur hexafluoride (SF6) gases were used as protective atmosphere during melting and casting. The castability of the AZ31-B strips was investigated for a smooth, low carbon steel substrate, and six copper substrates with various textures and roughnesses. Graphite powder was used to coat the substrates. The correlation between strip thickness and heat flux was investigated. It was found that the heat flux from the forming strip to the copper substrate was higher than that to the steel substrate, while coated substrates registered lower heat fluxes than uncoated substrates. The highest heat flux from the strip was recorded for casting on macrotextured copper substrates with 0.15？mm grooves. As the thickness of the strip decreased, the net heat flux decreased. As the heat flux increased, the grain sizes of the strips were reduced, and the SDAS decreased. The mechanical properties were improved when the heat flux increased. The black layers which formed on the strips’ surfaces were analyzed and identified as nanoscale MgO particles. Nano-Scale particles act as light traps and appeared black. 1. Introduction Magnesium is the lightest structural metal in common use [1]. Similarly, supplies of magnesium ores are virtually inexhaustible. Magnesium alloys normally have very good castability and machinability, as well as excellent specific strength and stiffness [2]. However magnesium alloys have some difficulty during rolling due to hexagonal close packed (hcp) lattice structure [3]. Meanwhile, a fine grain structure increases strength and ductility by promoting the operation of nonbasal slip systems and limiting twinning in magnesium alloys [4]. Strip casting of magnesium has become important in recent years. For reducing the cost of thin sheets of magnesium alloys, strip casting technologies such as horizontal single belt casting (HSBC), twin roll casting (TRC), and twin belt casting (TBC) have been developed [3]. With a strip casting process, magnesium alloy strips can typically be produced in thicknesses of 1–10？mm [1]. Direct strip casting, or HSBC, as a near-net-shape casting process, has potential use in the processing of aluminum, copper, zinc, and lead alloys, directly into sheet products. Generally, most metals and alloys are amenable to direct casting into plates, strips, or ribbons. However, a metallurgical understanding of these materials is needed to determine their suitability for casting into
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