One new casting topic is semisolid casting technology. It requires solid–liquid coexistence in slurry containing fine and globular crystals surrounded by liquid metal. The authors have made such the slurry using an inclined cooling plate and continuously cast AZ91 and AZ31 magnesium alloys. The factors that influence the best slurry with fine and globular crystals are the casting temperature and the length and inclination angle of the cooling plate. This investigation describes the best casting and cooling plate conditions to make semisolid slurry of AS41B magnesium alloy. The best conditions are then applied to produce continuous casting billets of AS41B magnesium alloy using an inclined cooling plate and a horizontal continuous casting machine. A 60 mm diameter AS41B billet was successfully obtained, and globular crystals (average size 57 μm) appear in the microstructures.