Microstructure of laser melted Zn-Al-based alloy

The microstructure of a laser treated eutectoid Zn-Al-based alloy (Zn-22% Al-2% Cu, in wt.%) has been investigated using X-ray diffraction (XRD), back-scattered scanning electron microscopy (BSEM) techniques. The alloy specimen was previously furnace cooled, then treated by continuous laser scanning. Various microstructures were observed in the laser treated alloy specimen. The molten zone is composed mainly of a fine dendritic structure of zinc-rich beta(s)'-phase. In the intermediate region between the molten zone and the bulk part of the specimen, a typical dendritic structure of cast eutectoid alloy is formed, i.e. an aluminum-rich alpha(s)'-phase as the core of the dendrites, surrounded by beta(s)'-phase. Zinc-rich -eta- and epsilon-phases form in the inter-dendritic region. These were distinct from the lamellar structure in the bulk part of the specimen. The effect of laser scan speed on the microstructure and phase transformation of various metastable phases in the alloy is also discussed. (C) 2003 Elsevier Science B.V. All rights reserved.