Microstructure evolution of a Zn-4wt.% Cu hyperperitectic alloy under laser surface remelting

Laser surface remelting experiments on Zn-4.0wt.%Cu hyperperitectic alloy have been performed on a 5kW CW CO₂ laser with the scanning velocities between 6 and 1207mm/s. Microstructures in both longitudinal and transverse section of the molten pools have been analyzed by optical microscope and SEM technique, and the average composition in the molten pools has been measured by Electron Probe Microanalysis(EPMA). With the increasing of growth rate, the microstructures of Zn-4.0 wt.%Cu alloy change from planar interface to lamellar structures and then cellular structures, and finally to absolute stability planar interface at a growth rate of 562mm/s, which shows reasonable agreement with that predicted by M-S theory.