Patent ID: 7028749

Claim:
A process for the production of magnesium alloy strip, by twin roll casting, wherein the process includes the steps of: (a) passing molten alloy from a source of supply to a feeding device; (b) feeding molten alloy from the feeding device through a nozzle to a chamber formed between an elongate outlet of the nozzle and a pair of substantially parallel rolls which are spaced one above the other to define a bite therebetween; (c) rotating said rolls in opposite directions whereby alloy is drawn from the chamber through the bite simultaneously with the feeding of step (b); and (d) flowing coolant fluid through each roll during the rotating step (c) to provide internal cooling of the rolls and thereby cooling alloy received in the chamber by heat energy extraction by the cooled rolls whereby substantially complete solidification of the magnesium alloy is achieved in the chamber prior to alloy passing through the bite defined between rolls and issuing therefrom as hot rolled alloy strip; and wherein the process further includes: maintaining alloy held at the source at a temperature sufficient to maintain alloy in the feed device at a superheated temperature above its liquidus temperature for the alloy; maintaining a depth of molten alloy in the feed device at a sufficient, controlled, substantially constant height of molten alloy above a centreline of the bite in a plane containing the axes of the rolls; and maintaining heat energy extraction by the cooled rolls in step (c) at a level sufficient to maintain alloy strip issuing from the bite at a surface temperature below about 400° C.; whereby the hot rolled alloy strip is substantially free of cracks and has good surface quality.