Microstructures in rapidly solidified Mg–Mn

Abstract

A Mg–2 wt-%Mn alloy has been rapidly solidified by melt spinning to produce ribbons 200–300 μm thick, 3–10 mm wide, and up to 0·3 m long. The solidification microstructure has been analysed by optical microscopy, conventional and scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, and focused-probe microdiffraction. The rapid solidification resulted in Mg grain sizes between 10 and 20 μm. In regions extending from the substrate and partly through the thickness, the solidification structure was cellular with cell spacings between 1 and 2 μm. This structure exhibited an enriched Mn content between cells, an unusual segregation pattern for a peritectic system. The cell boundaries were decorated by rod-shaped particles, 10–20 nm long, of the metastable phase β-Mn. Outside the cellular region the solidification structure was similar to that of conventionally cast material. There were some coarse β-Mn particles of ~ 0·1 μm dia., probably as a result of precipitation from the melt.

MST/134