Evolution of the Microstructure and Phase Composition of the Al–15 wt.% Fe Powder Alloy During Its Consolidation

Abstract

The evolution of the microstructure and phase composition of the Al–15 wt.% Fe powder alloy during pressing and sintering was studied. The structure of the starting powders, produced by melt atomization, was found to be multiphase and consisted of a solid-solution α-Al matrix and Al₆Fe and Al₁₃Fe₄ intermetallic compounds. The presence of the metastable Al₆Fe phase was attributed to the high cooling rates in the powder production by melt atomization. The sintering of green compacts prepared from the alloy powders involved negative shrinkage, which increased with higher sintering temperature, holding time, and compaction pressure for the starting samples. A potential cause of this phenomenon is the transformation of the metastable Al₆Fe phase into Al₁₃Fe₄, having a greater specific volume. Under solid-state sintering conditions at 500–600°C, the structure of the compacted samples remained fine-grained and included both the metastable Al₆Fe and stable Al₁₃Fe₄ phases. This promoted favorable conditions for achieving enhanced mechanical properties through the precipitation strengthening effect. In contrast, sintering at 800°C, accompanied by the formation of a liquid phase, led to recrystallization and formation of predominantly coarse Al₁₃Fe₄ crystals. This microstructural evolution diminished the strengthening effect provided by fine intermetallic phases. It was demonstrated that a sintering temperature of 600°C was optimal for retaining the metastable Al₆Fe phase in the alloy structure, allowing its transformation to be avoided and ensuring a controlled level of shrinkage during consolidation. The results may be useful for optimizing the technology for producing Al–Fe-based components with improved mechanical properties.