Recrystallisation of magnesium alloys containing rare-earth elements

The static recrystallisation behaviour of two magnesium alloys after hot rolling have been examined. The alloys chosen for study were the conventional alloy AZ31, and an alloy containing the rare earth element Gadolinium. The recrystallisation kinetics were lower for the rareearth alloy at low annealing temperatures, but at high annealing temperatures the kinetics were higher for the rare-earth alloy. It is suggested that this change in the comparative recrystallisation kinetics is a result of the improved mobility of the rare-earth solute at higher temperatures. This affects the recrystallisation kinetics through solute partitioning to the grain boundaries. The effect of this segregation on the recrystallisation texture is also discussed.

Influence of surface mechanical attrition treatment attrition media on the surface contamination and corrosion of magnesium

Surface mechanical attrition treatment (SMAT) is a mechanical peening process used to generate ultrafine grain surfaces on a metal. SMAT was carried out on pure magnesium using different attrition media (zirconia [ZiO2], alumina [Al2O3], and steel balls) to observe the effect on microstructure, surface residual stress, surface composition, and corrosion. Surface contamination from SMAT was characterized using glow discharge optical emission spectroscopy (GDOES). The SMAT process produced a refined grain structure on the surface of Mg but resulted in a region of elemental contamination extending ~10 μm into the substrate, regardless of the media used. Consequently, SMAT-treated surfaces showed an increased corrosion rate compared to untreated Mg, primarily through increased cathodic kinetics. This study highlights the issue of contamination resulting from the SMAT process, which is a penalty that accompanies the significant grain refinement of the surface produced by SMAT. This must be considered if attempting to exploit grain refinement for improving corrosion resistance.

Zirconium, calcium, and strontium contents in magnesium based biodegradable alloys modulate the efficiency of implant-induced osseointegration

Development of new biodegradable implants and devices is necessary to meet the increasing needs of regenerative orthopedic procedures. An important consideration while formulating new implant materials is that they should physicochemically and biologically mimic bone-like properties. In earlier studies, we have developed and characterized magnesium based biodegradable alloys, in particular magnesium-zirconium (Mg-Zr) alloys. Here we have reported the biological properties of four Mg-Zr alloys containing different quantities of strontium or calcium. The alloys were implanted in small cavities made in femur bones of New Zealand White rabbits, and the quantitative and qualitative assessments of newly induced bone tissue were carried out. A total of 30 experimental animals, three for each implant type, were studied, and bone induction was assessed by histological, immunohistochemical and radiological methods; cavities in the femurs with no implants and observed for the same period of time were kept as controls. Our results showed that Mg-Zr alloys containing appropriate quantities of strontium were more efficient in inducing good quality mineralized bone than other alloys. Our results have been discussed in the context of physicochemical and biological properties of the alloys, and they could be very useful in determining the nature of future generations of biodegradable orthopedic implants.

Addition of magnesium chloride to enhance mono-dispersity of a coiled-coil recombinant mouse macrophage protein

X-ray crystallography for the determination of three-dimensional structures of protein macromolecules represents an important tool in function assignment of uncharacterized proteins. However, crystallisation is often difficult to achieve. A protein sample fully characterized in terms of dispersity may increase the likelihood of successful crystallisation by improving the predictability of the crystallisation process. To maximize the probability of crystallisation of a novel mouse macrophage protein (rMMP), target molecule was characterized and refined to improve monodispersity. Addition of MgCl2 at low concentrations resolves the rMMP into a monodisperse solution, and finally successful crystallization of rMMP was achieved. The effect of MgCl2 was studied using gel filtration chromatography and dynamic light scattering.

A physically based phenomenological model for deformation twinning in magnesium alloy

A partial differential equation is developed that captures the evolution of key characteristics of tensile twinning in magnesium base alloys. The objective is to provide a framework for ascertaining the effects of hardening – due to grain refinement, precipitation and dislocation substructure – on twin volume fraction, thickness and length. The model is developed with the help of observations made on alloy AZ31. It is shown that it is necessary to consider the nucleation of twins at locations where neighbouring twins impinge on the grain boundary. The model provides a reasonable approximation for the role of grain size on twinning. It predicts a period of low apparent work hardening following yielding and shows that this should be more extensive for finer grain sizes, in agreement with experiment. Finally, some predictions are made on the effect of changing the resistance to twinning.

A comparison of maternal calcium and magnesium levels in pre-eclamptic and normotensive pregnancies: an observational case–control study

Objective : Supplementing pregnant women at high risk of developing pre-eclampsia with calcium may reduce the incidence of the disease. This study examines differences in serum and hair concentrations of calcium and magnesium between women with pre-eclamptic and normotensive pregnancies.Design : Observational case–control study.Setting : Two teaching hospitals in Cape Town, South Africa.PopulationWomen with pre-eclamptic (N = 96) or normotensive (N = 96) pregnancies, who delivered a single, live infant.MethodsDemographic and current pregnancy details were retrieved from clinical notes. Each participant completed a dietary questionnaire. Venous blood samples were taken from each participant to assess serum calcium and magnesium concentrations. Hair samples were obtained from all participants and calcium and magnesium levels were measured by inductively coupled plasma optical emission spectrometry (ICPOES).Main outcome measureHair and serum calcium and magnesium concentrations were compared between women with pre-eclamptic and normotensive pregnancies.ResultsDiet and socio-economic status in the two groups were similar. There was no significant difference in the hair calcium level between women with pre-eclamptic [1241 parts per million (ppm); range, 331–4654 ppm] and normotensive (1146 ppm; range, 480–4136 ppm) pregnancies (P = 0.5). Hair calcium levels in both groups were not affected by HIV infection.ConclusionWoman with pre-eclampsia showed no difference in chronic calcium status relative to normotensive women. This finding does not support the current belief that the mechanism by which calcium supplementation reduces the risk of developing pre-eclampsia is by correcting a nutritional deficiency.