Mechanical property behaviour of rheocast 319 alloys with and without iron additions

摘要

Cast aluminum alloys have witnessed a notable increase in use in the automotive and transport industry by virtue of their mechanical properties. The ability of these alloys to be easily cast into complex shapes coupled with a favourable strength-to-weight ratio has given them an edge over cast irons. Cast 319 alloys, for example, are heavily used in the fabrication of engine blocks. The addition of copper in these alloys aids in maintaining high mechanical properties in service, at temperatures of more than 200\ub0C. 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 a slurry with flow properties that resemble both solid and liquid. In the present work, the effects of iron additions and heat treatment to the mechanical properties of a 319 semi-solid alloy were studied. This alloy was prepared using the SEED process, developed by Rio Tinto Alcan (RTA) in collaboration with the Aluminium Technology Centre (ATC) 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. The rheocasting process is characterized by very good mechanical properties owing to a globular microstructure, which was confirmed via optical and scanning electron microscopy. Typical values of peak stress and elongation recorded in this work were ~350 MPa and ~5%, respectively. 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\u2019\u2019 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.