TWIN ROLL CASTING OF THIN AZ31 MAGNESIUM ALLOY STRIP WITH UNIFORM MICROSTRUCTURE AND CHEMISTRY

摘要

Magnesium alloys produced by the existing twin roll casting(TRC) technique have coarse and non-uniform microstructuresand severe centre-line segregation. Consequenty, TRC strip is casttypically no thinner than 5-9 mm, relying on costly subsequentdownstream processing to produce thin strip with an improvedmicrostructure. In the research described herein melt conditioningby intensive melt shearing was used prior to TRC to promoteheterogeneous nucleation and provide a refined and uniformmicrostructure without severe macrosegregation. Additionally, aTRC machine with small diameter rolls was used to cast AZ31strip of less than 2 mm in thickness suitable for direct componentmanufacturing such as stamping, without the necessity of hotrolling. The effects of process parameters, such as casting speedand melt superheat, on as-cast microstructure were studied.Experimental results show that the melt conditioning processprovided considerable reduction in as-cast grain size andelimination of centre-line segregation. The texture and mechanicalproperties of melt conditioned strips were much improved overconventional TRC strips, offering the potential for higher qualityfinal components.