Comparative atmospheric corrosion of primary and cold rolled copper in Australia

Atmospheric corrosion tests, according to ASTM G50, have been carried out in Queensland, Australia, at three different sites representing three different environmental conditions. A range of materials including primary copper (electrosheet) and electrolytic tough pitch (traditional cold rolled) copper have been exposed. Data is available for five exposure periods over a three year time span. X-Ray Diffraction has been used to determine the composition of the corrosion products. Corrosion rates have been determined for each material at each of the exposure sites and are compared with corrosion rates obtained from other long term atmospheric corrosion test programs. Primary copper sheet (electrosheet) behaves like traditionally produced cold rolled copper (C11000) sheet but with an increased corrosion rate. This difference between the rolled copper samples and the primary copper samples is probably due to a combination of factors related to the difference in crystallographic texture of the underlying copper, the morphology and texture of the cuprite layer, the surface roughness of the sheets, and the differences in mass. These factors combine together to provide an increased oxidation rate and TOW for the electrosheet material and which is significantly higher at the more tropical sites. For a sulfate environment (Urban) the initial corrosion product is cuprite with posnjakite and brochantite also occurring at longer exposures. Posnjakite is either washed away or converted to brochantite during further exposure. The amount of brochantite increases with exposure time and forms the blue-green patina layer. For a chloride environment (Marine) the initial corrosion product is cuprite with atacamite also occurring at longer exposures.

Comments on edge-to-edge matching and the equivalence of the invariant line, Delta g and Moire fringe approaches to the crystallographic features of precipitates

Three apparently distinct and different approaches have been proposed to account for the crystallographic features of diffusion-controlled precipitation. These three models are based on (a) an invariant line in the habit plane, (b) the parallelism of a pair of Deltags that are perpendicular to the habit plane and (c) the parallelism of a pair of Moire fringes that are in turn parallel to the habit plane. The purpose of the present paper is to show that these approaches are in fact absolutely equivalent and that when certain conditions are satisfied they are essentially the same as the recent edge-to-edge matching model put forward by the authors. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The prediction and representation of phase equilibria and physicochemical properties in complex slag systems

The development of new experimental techniques for the determination of phase equilibria in complex slag systems, chemical thermodynamic, and viscosity models is reported. The new experimental data, and new thermodynamic and viscosity models, have been combined in a custom-designed computer software package to produce limiting operability diagrams for slag systems. These diagrams are used to describe phase equilibria and physicochemical properties in complex slag systems. The approach is illustrated with calculations on the system FeO-Fe2O3-CaO-SiO-Al2O3 at metallic iron saturation, slags produced in coal slagging gasifiers, and in the reprocessing of nonferrous smelting slags. This article was presented at the Mills Symposium Molten Metals, Slags and Glasses-Characterisation of Properties and Phenomena held in London in August 2000.

Phase-equilibrium data and liquidus for the system "MnO"-CaO-Al2O3-SiO2 at Al2O3/SiO2 of 0.55 and 0.65

Phase-equilibrium data and liquidus isotherms for the system MnO-CaO-(Al2O3 + SiO2) at silicomanganese alloy saturation have been determined in the temperature range of 1373 to 1723 K. The results are presented in the form of the pseudoternary sections MnO-CaO-(Al2O3 + SiO2) with Al2O3/SiO2 weight ratios of 0.55 and 0.65. The primary-phase fields have been identified in this range of conditions.

The effect of the CaO/SiO2 ratio on the phase equilibria in the ZnO-“Fe2O3”-(PbO + CaO + SiO2) system in air: CaO/SiO2 = 0.1, PbO/(CaO + SiO2) = 6.2, and CaO/SiO2 = 0.6, PbO/(CaO + SiO2) = 4.3

Experimental studies on phase equilibria in the multi-component system PbO-ZnO-CaO-SiO2-FeO-Fe2O3 in air have been conducted to characterize the phase relations of a complex slag system used in the oxidation smelting of lead and in typical lead blast furnace sinters. The liquidus in two pseudoternary sections ZnO-Fe2O3-(PbO + CaO + SiO2) with the CaO/SiO2 weight ratio of 0.1 and the PbO/(CaO + SiO2) weight ratio of 6.2, and with CaO/SiO2 weight ratio of 0.6 and the PbO/(CaO + SiO2) weight ratio of 4.3, have been constructed.

Effect of iron on grain refinement of high-purity MG-Al alloys

The effect of iron on the grain refinement of high-purity Mg-3%Al and Mg-91%Al alloys has been investigated using anhydrous FeCl3 as an iron additive at 750degreesC in carbon-free aluminium titanite crucibles. It was shown that grain refinement was readily achievable for both alloys. Fe- and Al-rich intermetallic particles were observed in many magnesium grains. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Semisolid microstructural evolution of AlSi7Mg alloy during partial remelting

Different as-cast microstructures of an AlSi7Mg alloy were produced by controlling the solidification conditions. The as-cast grain size ranged from 1.4 mm to 160 mum and the morphology varied from dendritic to rosette-like to globular. The as-cast materials were then partially remelted and isothermally held at 580degreesC for microstructure evolution. The final microstructure depended on the initial as-cast microstructure and the isothermal holding time. After partial remelting and isothermal holding, coarse-grained dendritic structures were not able to evolve to a globular structure, while structures with medium sized dendritic grains evolved to a globular structure with a relatively large particle size after a long isothermal holding time. Fine-grained structures evolved to well-rounded globular grains within times ranging front 10 min to 5 min as the dendritic nature of the starting structure diminished. An empirical equation has been established to describe the relationship between the evolved microstructure and the as-cast microstructure. (C) 2003 Elsevier B.V. All rights reserved.

Grain coarsening of magnesium alloys by beryllium

A trace of beryllium can lead to dramatic grain coarsening in Mg-Al alloys at normal cooling rates. It is, however, unclear whether this effect applies to aluminium-free magnesium alloys or not. This work shows that a trace of beryllium also causes considerable grain coarsening in Mg-Zn, Mg-Ca, Mg-Ce and Mg-Nd alloys and hinders grain refinement of magnesium alloys by zirconium as well. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Discussions on grain refinement of magnesium alloys by carbon inoculation

Carbon inoculation has no effect on magnesium alloys that do not contain aluminium. The hypothesis proposed in a recent article [Scripta Materialia 49 (2003) 1129] that segregation of carbon plays a major role in the grain refinement of magnesium alloys by carbon inoculation is inconsistent with many of the observed facts. The Al4C3 or Al-C-O hypothesis, which is supported by experimental observations, is still the most reasonable mechanism proposed to date for the grain refinement of magnesium alloys by carbon inoculation. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Native grain refinement of magnesium alloys

High purity Mg-Al type alloys have a naturally fine grain size compared to commercial purity alloys with the same basic composition. This is referred to as native grain refinement. It is shown that native grain refinement occurs only in magnesium alloys containing aluminium. The mechanism is attributed to the Al4C3 particles existing in these alloys. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Age hardening of a sintered Al-Cu-Mg-Si-(Sn) alloy

The age hardening response of a sintered Al-3.8 wt% Cu-1.0 wt% Mg-0.70 wt% Si alloy with and without 0.1 wt% Sn was investigated. The sequence of precipitation was characterised using transmission electron microscopy. The ageing response of the sintered Al-Cu-Mg-Si-(Sn) alloy is similar to that of cognate wrought 2xxx series alloys. Peak hardness was associated with a fine, uniform dispersion of lath shaped precipitates, believed to be either the betaor Q phase, oriented along < 010 >. directions and theta' plates lying on {001}(alpha). planes. Natural ageing also resulted in comparable behaviour to that observed in wrought alloys. Porosity in the powder metallurgy alloys did not significantly affect the kinetics of precipitation during artificial ageing. Trace levels of tin, used to aid sintering, slightly reduced the hardening response of the alloy. However, this was compensated for by significant improvements in density and hardness. (c) 2005 Elsevier B.V. All rights reserved.