Powder forging of a sintered Al-3.8Cu-1Mg-0.8Si-O.1Sn alloy

The forging characteristics of an Al-Cu-Mg-Si-Sn alloy are examined using it new testing strategy which incorporates a double truncated cone specimen and finite element modelling. This sample geometry produces controlled strain distributions within a single specimen and can readily identify the specific strain required to achieve a specific microstructural event by matching the metallographic data with the strain profiles calculated from finite element software, The friction conditions were determined using the conventional friction ring test, which was evaluated using finite element software. The rheological properties of the alloy, evaluated from compression testing of right cylinders, are similar to the properties of conventional aluminium forgings. A hoop strain develops at the outer diameter of the truncated cones and this leads to pore opening at the outer few millimetres. The porosity is effectively removed when the total strain equals the net compressive strain. The strain profiles that develop in the truncated cones are largely independent of the processing temperature and the strain rate although the strain required for pore closure increases as the forging temperature is reduced. This suggests that the microstructure and the strain rate sensitivity may also be important factors controlling pore behaviour. (C) 2002 Elsevier Science B.V. All rights reserved.

Electrochemical deposition of cupric ions for the determination of mass transfer rates to a stepped rotating cylinder electrode

The stepped rotating cylinder electrode (SRCE) geometry has been developed as a simple aid to the practical study of the flow-enhanced corrosion and applied electrochemistry problems commonly observed under conditions of disturbed, turbulent flow. The electrodeposition of cupric ions from an acid sulphate plating bath has been used to characterise differential rates of mass transfer to the SRCE. The variation in thickness of electrodeposited copperfilms has allowed the mapping of local rates of mass transfer over the active surface of this geometry. Both optical and scanning electron microscopy were used for the examination of metallographic sections to provide a high resolution evaluation of the distribution of mass transfer coefficient. Results are also discussed using the convective-diffusion model in combination with the existing direct numerical flow simulation (DNS) data for this geometry.

Grain size measurements in Mg-Al high pressure die castings using electron back-scattered diffraction (EBSD)

Optical metallographic techniques for grain-size measurement give unreliable results for high pressure diecast Mg-Al alloys and electron back-scattered diffraction mapping (EBSD) provides a good tool for improving the quality of these measurements. An application of EBSD mapping to this question is described, and data for some castings are presented. Ion-beam milling was needed to prepare suitable samples, and this technique is detailed. As is well-known for high pressure die castings, the grain size distribution comprises at least two populations. The mean grain size of the fine-grained population was similar in both AZ91 and AM60 and in two casting thicknesses (2 mm and 5 mm) and, contrary to previously published reports, it did not vary with depth below the surface.

Observations of the reduction of FeO from slag by graphite, coke and coal char

The reduction of FeO from iron-saturated FeO-CaO-Al2O3-SiO2 slags by graphite, coke and coal char at 1 673 K has been investigated using a sessile drop technique. Metallographic analysis of samples quenched from the reaction temperature, and in situ observations of the reaction interface, reveal significant differences in the slag/carbon contact, and in the morphologies of the product iron and its composition; these differences were found to depend on the carbon type used in the reduction. In particular it has been shown that, in the case of graphite and coke, liquid Fe-C droplets were rapidly formed at the slag/C interface. Reactions of the slag with coal chars, in contrast, result predominantly in the formation of solid iron. These observations indicate that the reaction pathways, and hence reaction kinetics, are dependent on carbon type.