An investigation of dilute Al-Hf and Al-Hf-Si alloys

To meet the demand for extruded aluminium alloys tolerant of temperatures up to 600 degreesC, highly stable microstructures with the ability to maintain strength at such temperatures are required. Such alloys are presently not available commercially, however, by adding elements that form a homogeneous and dense distribution of thermally stable dispersoids, this may be achieved. A relatively untried element in this respect is hafnium (Hf), which may lead to a significant increase in the recrystallisation resistance/structural stability. By subjecting the alloy to a carefully chosen homogenisation treatment, fully coherent Al3Hf-dispersoids may form. In the current investigation a binary Al-Hf alloy and a ternary Al-Hf-Si alloy have been investigated. It has been found that Si enhances the Al3Hf-precipitation in these alloys. However, the results indicate that the Si-content should be kept below 0.15 wt.% in order to avoid the formation of AlHfSi-phases. (C) 2004 Elsevier B.V. All rights reserved.