Extrusion processing parameter–mechanical property correlations in rapidly solidified Al–6·7Fe–5·9Ce and Al–6·2Fe–5·9Ce–1·63Si (wt-%) alloy powders

Abstract

High temperature aluminium alloys containing iron and cerium additions have promising mechanical properties, particularly with regard to thermal 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 high volume fraction of strengthening dispersoids depending on the cooling rate. To retain the microstructural advantages of rapid solidification, 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 homogeneity of microstructure produced by higher processing temperature leads to improved ductility and toughness. The present investigation was undertaken to find suitable extrusion processing conditions for two rapidly 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 added 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 the Al12(Fe,V)3Si phase in the Al–Fe–V–Si system). Both the alloys were extruded in the temperature range 400–500°C at a constant extrusion ratio of approximately 10:1 and ram speed of 3 mm s−1. The room temperature mechanical properties of all the extrudates were measured 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 extrudates processed at 400 and 450°C. The results obtained for the low temperature (400°C) extrudate were found to be satisfactory when compared with US Air Force Materials Laboratory (AFML) goals for high temperature aluminium alloys. Attempts have been made to explain the properties on the basis of the microstructures of the extrudates, which were characterised using transmission and scanning electron microscopy and X-ray diffraction.MST/1615