Magnesium alloys, especially precipitation hardened alloys, are used in casting. Sand, permanent mold and die casting methods are used, but plaster-of-Paris casting has not yet been perfected. Sand casting in green-sand molds requires a special technique, because the magnesium reacts with moisture in the sand, forming magnesium oxide and liberating hydrogen. The oxide forms blackened areas called burns on the surface of the casting, and the liberated hydrogen may cause porosity. Inhibitors such as sulfur, boric acid, ethyl glycol, or ammonium fluoride are mixed with the damp sand to prevent the reaction. All gravity-fed molds require an extra high column of molten metal to make the pressure great enough to force gas bubbles out of the casting and make the metal take the detail of the mold. The thickness of the casting wall should be at least 5/32 in. under most conditions. Extra-large fillets must be provided at all re-entrant corners, since stress concentration in magnesium castings are particularly dangerous. Permanent mold castings are made from the same alloys and have about the same physical properties as sand castings. Since the solidification shrinkage of magnesium is about the same as that of aluminium, aluminium molds can often be adapted to make magnesium-alloy castings (although it may be necessary to change the gating). Pressure cold-chamber castings are used for quantity production of small parts. The rapid solidification caused by contact of the fluid metal with the cold die produces a casting of dense structure with excellent physical properties. The finish and dimensional accuracy are very good, and machining is necessary only where extreme accuracy is required. Usually these castings are not heat treated.
Zimag could provide cast magnesium alloys of AM60B & AZ91D now.
AM60B: Most popular magnesium material with high strength & perfect casting performance, like: bicycle, motorcycle, automobile, computers, communication equipments, consumer products, sports appliances, hand tools and so on.
AZ91D: High elongation & good impact strength, like: steering wheel, engine cover.