On hot deformation of aluminium-silicon powder metallurgy alloys

The growing field of aluminium powder metallurgy (PM) brings promise to an economical and environmental demand for the production of high strength, light weight aluminium engine components. In an effort to further enhance the mechanical properties of these alloys, the effects of hot upset forging sintered compacts were studied. This article details findings on the hot compression response of these alloys, modelling of this flow behaviour, and its effects on final density and microstructure. Two aluminium-silicon based PM alloys were used for comparison. One alloy was a hypereutectic blend known as Alumix-231 (Al-15Si-2.5Cu-0.5Mg) and the second was an experimental hypoeutectic system (Al-6Si-4.5Cu-0.5Mg). Using a Gleeble 1500D thermomechanical simulator, sintered cylinders of the alloys were upset forged at various temperatures and strain rates, and the resulting stress-strain trends were studied. The constitutive equations of hot deformation were used to model peak flow stresses for each alloy when forged between 360 and 480 degrees C, using strain rates of 0.005-5.0 s(-1). Both alloys benefited from hot deformation within the ranges studied. The experimental alloy achieved an average density of 99.6% (+/- 0.2%) while the commercial alloy achieved 98.3% (+/- 0.6%) of its theoretical density. It was found that the experimentally obtained peak flow stresses for each material studied could be very closely approximated using the semi-empirical Zener-Hollomon models.