A METHOD OF REDUCING THE FORMATION OF PRIMARY PLATLET-SHAPED BETA-PHASE IN IRON CONTAINING AlSi-ALLOYS, IN PARTICULAR IN Al-Si-Mn-Fe ALLOYS

摘要

Iron is a detrimental impurity in aluminium alloys since it causes hard and brittle iron-rich intermetallic phases to precipitate during solidification. The most detrimental phase in the microstructure is the beta-phase of the Al5FeSi-type because it is platelet-shaped. The present invention provides a method of producing iron-containing Al-alloys free from platelet-shaped beta-phase by controlling and regulating the precipitation path during solidification such that the precipitation of Fe containing intermetallic phases starts with the precipitation of the hexagonal phase of the Al8Fe2Si-type. The presence of the Al8Fe2Si-type phase result in that beta-phase will not develop the common platlet-morphology but nucleate on and cover the Al8Fe2Si-type phase which in turn has a less harmful morphology. Furthermore, the invention defines the use of thermal analysis as a means for controlling the morphology of the precipitates.