Corrosion resistance of aged die cast magnesium alloy AZ91D

The corrosion behaviour of die cast magnesium alloy AZ91D aged at 160degreesC was investigated. The corrosion rate of the alloy decreases with ageing time in the initial stages and then increases again at ageing times greater than 45 h. The dependence of the corrosion rate on ageing time can be related to the changes in microstructure and local composition during ageing. Precipitation of the beta phase (Mg17Al12) occurs exclusively along the grain boundaries during ageing. The beta phase acts as a barrier, resulting in a decreasing corrosion rate in the initial stages of ageing. In the later stages, the decreasing aluminium content of alpha grains makes the alpha matrix more active, causing an increase in the corrosion rate. Electrochemical testing results also confirm the combined effects of the changes in alpha and beta phases on the corrosion resistance of the aged die cast AZ91D alloy. (C) 2003 Elsevier B.V. All rights reserved.

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.

Evaluation of the BEASY program using linear and piecewise linear approaches for the boundary conditions

The boundary element method (BEM) was used to study galvanic corrosion using linear and logarithmic boundary conditions. The linear boundary condition was implemented by using the linear approach and the piecewise linear approach. The logarithmic boundary condition was implemented by the piecewise linear approach. The calculated potential and current density distribution were compared with the prior analytical results. For the linear boundary condition, the BEASY program using the linear approach and the piecewise linear approach gave accurate predictions of the potential and the galvanic current density distributions for varied electrolyte conditions, various film thicknesses, various electrolyte conductivities and various area ratio of anode/cathode. The 50-point piecewise linear method could be used with both linear and logarithmic polarization curves.

Resistance development in community-acquired strains of methicillin-resistant Staphylococcus aureus: an in vitro study

This study compares in vitro antimicrobial resistance development between strains of Staphylococcus aureus including newly described community-acquired methicillin-resistant strains (CA-MRSA). High-level resistance developed in all strains of S. aureus after exposure to rifampicin and gentamicin and in some strains after fusidic acid exposure, independent of methicillin resistance phenotype. Resistance did not develop after exposure to clindamycin, cotrimoxazole, ciprofloxacin, linezolid, or vancomycin. These results have important implications for therapy of CA-MRSA infections. (C) 2004 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.

Eutectic grains in unmodified and strontium-modified hypoeutectic aluminum-silicon alloys

Additions of strontium to hypoeutectic aluminum-silicon alloys modify the morphology of the eutectic silicon phase from a coarse platelike structure to a fine fibrous structure. Thermal analysis, interrupted solidification, and microstructural examination of sand castings in this work revealed that, in addition to a change in silicon morphology, modification with strontium also causes an increase in the size of eutectic grains. The eutectic grain size increases because fewer grains nucleate, possibly due to poisoning of the phosphorus-based nucleants, that are active in the unmodified alloy. A simple growth model is developed to estimate the interface velocity during solidification of a eutectic grain. The model confirms, independent of microstructural observations, that the addition of 100 ppm strontium increases the eutectic grain size by at least an order of magnitude compared with the equivalent unmodified alloy. The model predicts that the growth velocity varies significantly during eutectic growth. At low strontium levels, these variations may be sufficient to cause transitions between flake and fibrous silicon morphologies depending on the casting conditions. The model can be used to rationally interpret the eutectic grain structure and silicon morphology of fully solidified aluminum-silicon castings and, when coupled with reliable thermal data, can be used to estimate the eutectic grain size.

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.

Web-based screening and brief intervention for hazardous drinking: a double-blind randomized controlled trial

Background Strong evidence exists for the efficacy of screening and brief intervention for reducing hazardous drinking. However, problems have been highlighted with respect to its implementation in health-care systems, not least of which is a reluctance of some doctors to discuss alcohol proactively with their patients. Aims To determine the efficacy of a novel web-based screening and brief intervention (e-SBI) to reduce hazardous drinking. Design A double-blind randomized controlled trial. Setting A university student health service. Participants A total of 16 7 students (17-26 years) were recruited in the reception area and completed a 3-minute web-based screen including the Alcohol Use Disorder Identifiation Test (AUDIT) questionnaire. Of these, 112 tested positive, and 104 (52 females) who consented to follow-up were included in the trial. Measurements Drinking frequency, typical occasion quantity, total volume, heavy episode frequency (females > 80 g ethanol, males > 120 g ethanol), number of personal problems, an academic problems score. Intervention Participants were randomized to 10-15 minutes of web-based assessment and personalized feedback on their drinking (intervention, n = 5 1) or to a leaflet-only control group (n = 5 3). Findings Mean baseline AUDIT scores for control and intervention groups were 16.6 (SD = 6.0) and 16.6 (SD = 5.7). At 6 weeks, participants receiving e-SBI reported significantly lower total consumption (geometric mean ratio = 0.74; 9 5 % confidence interval: 0.56-0.96), lower heavy episode frequency (0.63; 0.42-0.92) and fewer personal problems (0.70; 0.54-0.91). At 6 months personal problems remained lower (0.76; 0.60-0.97), although consumption did not differ significantly. At 6 months, academic problems were lower in the intervention group relative to controls (0.72; 0.51-1.02). Conclusions e-SBI reduced hazardous drinking among university students, to an extent similar to that found for practitioner-delivered brief interventions in the general population. e-SBI offers promise as a strategy to reduce alcohol-related harm in a way that is non-intrusive, appealing to the target group, and capable of being incorporated into primary care. Research is required to replicate the findings, to determine the duration of intervention effects, and to investigate the mechanisms by which the intervention operates.

Dynamic and steady-state rheology of Australian honeys at subzero temperatures

The rheology of 10 Australian honeys was investigated at temperatures -15C to 0C by a strain-controlled rheometer. The honeys exhibited Newtonian behavior irrespective of the temperature, and follow the Cox-Merz rule. G/G' and omega are quadratically related, and the crossover frequencies for liquid to solid transformation and relaxation times were obtained. The composition of the honeys correlates well (r(2) > 0.83) with the viscosity, and with 24 7 data sets (Australian and Greek honeys), the following equation was obtained: mu = 1.41 x 10(-17) exp [-1.20M + 0.01F - 0.0G + (18.6 X 10(3)/T)] The viscosity of the honeys showed a strong dependence on temperature, and four models were examined to describe this. The models gave good fits (r(2) > 0.95), but better fits were obtained for the WLF model using T-g of the honeys and mu(g) = 10(11) Pa.s. The WLF model with its universal values poorly predicted the viscosity, and the implications of the measured rheological behaviors of the honeys in their processing and handling are discussed.

Morphological features of interfacial intermetallics and interfacial reaction rate in Al-11Si-2.5Cu-(0.15/0.60)Fe cast alloy/die steel couples

Soldering reactions are commonly observed during high pressure die casting of aluminium alloys, and involve the formation and growth of interfacial intermetallics between the die and the cast alloy. It is generally believed that close to 1% Fe is necessary in the aluminium alloy to reduce soldering. However, the role of iron in the interfacial reaction has not been studied in detail. In this investigation, reaction couples were formed between H13 tool steel substrates and an Al-11Si-2.5Cu melt containing either 0.15 or 0.60% Fe. Examination revealed distinctly different intermetallic layer morphology. The overall growth and chemistry of the reaction layer and the reaction rate measured by the consumption of the substrate were compared for the two alloy melts. It was demonstrated that a higher iron content reduces the rate of interfacial reaction, consistent with an observed thicker compact ( solid) intermetallic layer. Hence, the difference in reaction rate can be explained by a significant reduction in the diffusion flux due to a thicker compact layer. Finally, the mechanism of the growth of a thicker compact layer in the higher iron melt is proposed, based on the phase relations and diffusion both within and near the interfacial reaction zone. (C) 2004 Kluwer Academic Publishers.

Impact of premorbid undernutrition on outcome in stroke patients

Background and Purpose - To assess the prevalence of premorbid undernutrition and its impact on outcomes 1 month after stroke. Methods - The study recruited from consecutive stroke admissions during a 10-month period. Premorbid nutritional status ( using the subjective global assessment [SGA]), premorbid functioning ( modified Rankin scale [MRS]), and stroke severity ( National Institutes of Health Stroke Scale [NIHSS] score) were assessed at admission. The associations between premorbid nutritional status, poor outcome ( defined as MRS greater than or equal to 3), and mortality were examined before and after adjustment for confounding variables, including age, gender, stroke risk factors, stroke severity, and admission serum albumin. Results - Thirty of 185 patients were assessed as having undernutrition at admission. Significant unadjusted associations were observed between undernutrition and poor outcome (odds ratio [OR], 3.4; 95% CI, 1.3 to 8.7; P = 0.01), and mortality (OR, 3.1, 95% CI, 1.3 to 7.7; P = 0.02) at 1 month. NIHSS, age, and premorbid MRS were also significantly associated with poor outcomes. After adjustment for these factors, the effect size of associations remained important but not significant ( poor outcome: OR, 2.4; 95% CI, 0.7 to 9.0, P = 0.18; mortality: OR, 3.2; 95% CI, 1.0 to 10.4, P = 0.05). Conclusions - Premorbid undernutrition, as assessed using the SGA, appears to be an independent predictor of poor stroke outcome. Stroke prevention strategies should target undernutrition in the population at risk for stroke to improve outcomes.

An analysis of the relationship between grain size, solute content, and the potency and number density of nucleant particles

To be able to determine the grain size obtained from the addition of a grain refining master alloy, the relationship between grain size (d), solute content (defined by the growth restriction factor Q), and the potency and number density of nucleant particles needs to be understood. A study was undertaken on aluminium alloys where additions of TiB2 and Ti were made to eight wrought aluminum alloys covering a range of alloying elements and compositions. It was found from analysis of the data that d = a/(3)root pct TiB2 + b/Q. From consideration of the experimental data and from further analysis of previously published data, it is shown that the coefficients a and b relate to characteristics of the nucleant particles added by a grain refiner. The term a is related to the maximum density of active TiB2 nucleant particles within the melt, while b is related to their potency. By using the analysis methodology presented in this article, the performance characteristics of different master alloys were defined and the effects of Zr and Si on the poisoning of grain refinement were illustrated.

Grain refinement efficiency and mechanism of aluminium carbide in Mg-Al alloys

Detailed microscopic examination using optical and electron microscopes suggests that Al4C3, often observed in the central regions of magnesium grains on polished sections, is a potent substrate for primary Mg. Calculations of the crystallographic relationships between magnesium and Al4C3 further support the experimental observations. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.