EFFECT OF VACUUM DEGASSING ON MECHANICAL-PROPERTIES OF 2 RAPIDLY SOLIDIFIED AL-FE ALLOYS FOR ELEVATED-TEMPERATURE APPLICATIONS

The use of powder metallurgy in the aluminium industry offers many adv antages, e.g., improved homogeneity, refined microstructures, novel al loy compositions, etc. However the presence of an aluminium oxide surf ace layer on the powder particles is the cause of some concern. This a luminium oxide is prone to hydration. The mechanical properties of pow er metallurgical aluminium alloys can be improved by uniformly distrib uting the aluminium oxide throughout the matrix. This successful distr ibution depends on the efficient removal of water from the hydrated ox ide. Vacuum degassing has been used to achieve this objective. The pre sent paper reports on the search for a suitable degassing temperature for two high temperature Al-Fe-Ce alloys consolidated by hot extrusion . Mass spectrometric analysis was carried out to determine the species evolved during degassing. The outgassed species were water, nitrogen, and oxygen. This analysis revealed no hydrogen evolution even at temp eratures as high as 430-degrees-C. Both room and elevated temperature mechanical properties of the degassed samples were evaluated and compa red with those of the non-degassed material extruded under identical c onditions. There is some marginal improvement in the ductility of the samples degassed at 330-degrees-C. The fracture toughness decreases wi th increase in degassing temperature. An attempt has been made to expl ain the observed mechanical properties in terms of the oxide distribut ion which is a direct consequence of the efficiency of degassing.