The influence of Saffil δ-alumina fibre reinforcement on gas entrapment and evolution in P/M Al-20Si-3Cu-1Mg- x Al2O3 composite

• Published in: Journal of materials science Vol. 28; no. 11; pp. 3103 - 3115
• Main Authors: Ter Haar, J. H., Duszczyk, J.
• Format: Journal Article
• Language: English
• Published: 01.06.1993
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/BF00354717

Compacts of an aluminium/alumina fibre composite, produced by a powder metallurgical (P/M) route, were the subject of a vacuum degassing study. The materials consisted of Al--20 wt.% Si--3 wt.% Cu--1 wt.% Mg pre-alloyed powder mixed with 0, 5 and 20 vol.% of Saffil delta -alumina fibres. The composition of gases liberated during heating at constant rate was monitored with a quadrupole mass spectrometer. Water and hydrogen were the main volatile products released. High water and H pressures were maintained longest by the composite with the highest volume fraction of fibres. The presence of fibres gave rise to delayed peak H production when compared to the matrix. Nitrogen adsorption analysis proved that the Saffil fibre RF Milled, possesses a large specific internal surface area and points towards the presence of very fine sized porosity. Thermogravimetric analyses confirmed a high water content of the fibres of at least 0.86 wt.%. Of this, condensed and adsorbed water constitute the largest fraction. Owing to the fineness of the porosity and consequently the low concentration gradients, time as well as temperature (for enhancement of diffusion) are equally important variables to be considered for effective degassing of these composites.