Microstructure evolution of laser surface remelted Zn-2.7 wt.%Cu hyperperitectic alloy

Laser surface remelting experiments on Zn-2.7 wt.%Cu hyperperitectic alloy were performed by using a 5kW CW CO₂ laser at beam scanning velocities ranging between 6 and 1,207 mm/s. With the increase of the growth rate, the microstructures of Zn-2.7 wt.% Cu alloy changed from planar interface to lamellar structures, cellular structures, and finally to high velocity absolute stability (HVAS) planar interface at a growth rate of 349 mm/s. The critical growth rate for the transformation from lamellar structure to cells was about 96 mm/s. Quantitative measurement was preformed to reveal the relationship between the average lamellar spacing and the corresponding growth rate, and the results are in excellent agreement with the prediction of the TMK eutectic model.