On the microstructure of rapidly solidified Al-15 wt pct mn ribbons: effect of annealing in the temperature range 300° to 600 °C

Abstract

A study has been made of the relationship between the microstructures formed in rapidly solidified Al-15 wt pct Mn ribbons and the precipitation processes following annealing in the regime 300° to 600 °C from 15 minutes to 100 hours. The as-melt spun ribbons exhibit the icosahedral structure (in an Al-matrix), which is found to be stable up to ∼320 °C as deduced from electrical resistivity measurements. X-ray and TEM analyses reveal that decomposition of this phase is detectable after annealing at 400 °C/1 h, giving rise to Al6Mn. At 450 °C, four phases, viz., the G, Al6Mn, G’, and G″ intermetallic phases, are observed (in addition to Al), which result from the direct decomposition of the icosahedral phase. At higher temperatures, only the Al6Mn phase + Al is observed. The effect of increase in annealing time is simply to coarsen the Al6Mn particles. Our X-ray and electron diffraction data favor the model proposed by Shechtman and Blech for the icosahedral structure. The investigations were carried out using density and electrical resistivity measurements, differential thermal analysis, as well as X-ray diffraction and optical and transmission electron microscopy.