Iron-related porosity in Al-Si-(Cu) foundry alloys

An experimental program has been undertaken to explore the effect of iron concentration on porosity levels in Al-Si alloy sand castings. The effect of iron concentrations above, below and equal to the critical iron content for alloys with either 5 or 9% Si and either 0, 1 or 3% Cu has been determined. Increasing iron concentrations were found to increase porosity in all alloys except the copper-containing Al-5% Si alloys which displayed a porosity minimum at the critical iron content. Porosity was observed to be higher in the Al-9% Si castings than the Al-5% Si castings. Differences in the primary phase volume fraction and morphology may explain this observation. The results of this experimental work do not support the existing published theories that have been proposed to explain the effect the iron on porosity. An alternative theory is therefore developed. (c) 2006 Elsevier B.V. All rights reserved.

An X-ray micro-fluorescence study to investigate the distribution of Al, Si, P and Ca ions in the surrounding soft tissue after implantation of a calcium phosphate-mullite ceramic composite in a rabbit animal model

Synthetic calcium phosphates, despite their bioactivity, are brittle. Calcium phosphate-mullite composites have been suggested as potential dental and bone replacement materials which exhibit increased toughness. Aluminium, present in mullite, has however been linked to bone demineralisation and neurotoxicity: it is therefore important to characterise the materials fully in order to understand their in vivo behaviour. The present work reports the compositional mapping of the interfacial region of a calcium phosphate-20 wt% mullite biocomposite/soft tissue interface, obtained from the samples implanted into the long bones of healthy rabbits according to standard protocols (ISO-10993) for up to 12 weeks. X-ray micro-fluorescence was used to map simultaneously the distribution of Al, P, Si and Ca across the ceramic-soft tissue interface. A well defined and sharp interface region was present between the ceramic and the surrounding soft tissue for each time period examined. The concentration of Al in the surrounding tissue was found to fall by two orders of magnitude, to the background level, within similar to 35 mu m of the implanted ceramic.