EXTRUSION PROCESSING PARAMETER MECHANICAL PROPERTY CORRELATIONS IN RAPIDLY SOLIDIFIED AL-6.7FE-5.9CE AND AL-6.2FE-5.9CE-1.63SI (WT-PERCENT)ALLOY POWDERS

High temperature aluminium alloys containing iron and cerium additions have promising mechanical properties, particularly with regard to the rmal stability. Development of these alloys has been possible because of advances in rapid solidification technology. The advantage of rapid solidification is that it produces extended solid solubility or a hig h volume fraction of strengthening dispersoids depending on the coolin g rate. To retain the microstructural advantages of rapid solidificati on, it has generally been thought necessary to process these alloys at the lowest possible temperature. The present work indicates that for optimum strength levels this is correct but that the greater homogenei ty of microstructure produced by higher processing temperature leads t o improved ductility and toughness. The present investigation was unde rtaken to find suitable extrusion processing conditions for two rapidl y solidified high temperature aluminium alloys having the compositions Al-6-7Fe-5-9Ce and Al-6.2Fe-5.9Ce-1.63Si (all wt-%). Silicon was adde d to Al-Fe-Ce in an attempt to form the Al12(Fe,Ce)3Si phase, which if formed might improve the thermal stability of the alloy (similar to t he Al12 (Fe,V)3Si phase in the Al-Fe-V-Si system). Both the alloys wer e extruded in the temperature range 400-500-degrees-C at a constant ex trusion ratio of approximately 10:1 and ram speed of 3 mm s-1. The roo m temperature mechanical properties of all the extrudates were measure d for both alloys and the values obtained were compared with those for other high temperature aluminium alloys such as Al-5Cr-2.2Zr and Al-8 .3Fe-4.8Zr. High temperature tensile properties were measured for extr udates processed at 400 and 450-degrees-C. The results obtained for th e low temperature (400-degrees-C) extrudate were found to be satisfact ory when compared with US Air Force Materials Laboratory (AFML) goals for high temperature aluminium alloys. Attempts have been made to expl ain the properties on the basis of the microstructures of the extrudat es, which were characterised using transmission and scanning electron microscopy and X-ray diffraction.