Mechanical Property Behaviour of Rheocast 319 Alloys with and without Iron Additions

Cast aluminum-silicon alloys have witnessed a notable increase in use in the automotive and transport industry. The ability of these alloys to be easily cast into complex shapes coupled with a favorable strength-to-weight ratio has given them an edge over cast irons. One particular area of casting which has received further and further attention is the area of semi-solid casting, where an alloy casting is prepared as slurry with flow properties that resemble both solid and liquid. In the present work, the effects of iron additions on the mechanical properties of a 319 semi-solid alloy were studied. This alloy was prepared using the SEED process, as developed by Rio Tinto Alcan in collaboration with the Aluminum Technology Centre of NRC Canada. The SEED (Swirled Enthalpy Equilibration Device) process is a novel rheocasting method which yields a semi-solid slurry from the mechanical stirring and cooling of the molten aluminum. This rheocasting process is characterized by very good mechanical properties owing to a globular microstructure. The SEED method has already proven successful in the case of 356/357 and 6061 alloys, for example, with fluid die filling, sound castings and good mechanical properties being reported. In addition, the production of large slugs of 6\mi diameter and more, capable of engine blocks, has been demonstrated and the possibility to dilute the standard high Fe and 9% Si die casting alloy A380 into a medium Fe, 6 to 7% Si alloy of the 319 type well suited to SEED has been successfully tested. The eventual aims of this study are to use recycled aluminum, containing iron traces, for future casting as well as to develop a fully industrial version of the SEED casting method.