Laser resolidification of a Zn-3.37 wt.% Cu peritectic alloy

Laser rapid solidification of a Zn-3.37 wt.% Cu alloy that span a peritectic reaction in its phase diagram, i.e. ξ+L→ηn, was performed at various scanning velocities between 12.7 and 23.3 mm s^-1. Solidification microstructures were characterized through both longitudinal and cross sections, showing three typical microstructures that were located in upper remelted zone, bottom remelted zone and partially-remelted zone of the laser pool, respectively. The observed microstructures containing plate-like cellular ηn with or without dendritic ε are consistent with our previous observations for the same alloy grown at velocities between 2.64 and 4.82 mm s^-1 using Bridgman solidification technique. The critical velocity of the transition from ε dendrite-free (fully cellular ηn) to ε dendrite-containing microstructure is evaluated on the basis of competitive growth, indicating an excellent agreement with our experimental results in Zn-rich Zn-Cu alloys processed by both Bridgman solidification and laser surface remelting techniques. The intercellular spacing (%) of n cells decreases from 8.0 to 1.5 um with increasing growth velocity from 1.0 to 19.1 mm s^-1 such that %V⁰.⁵⁹ is constant in parametric agreement with the predictions of Hunt-Lu model. Vickers microhardness measurements were carried out along cross section of the laser remelted zone, showing that the highest value of about 140 HV was obtained in comparison with that of the original substrate alloys of 90 HV.