Diffusion couple investigation of the Mg-Zn system

Abstract

Growing use and development of lightweight Mg alloys has been the catalyst for more fundamental research in Mg based material systems to be completed. Zinc is one of the most common alloying elements in Mg alloys. Phase layer growth and interdiffusion in the binary Mg-Zn system was investigated utilizing solid-to-solid diffusion couples. Anneals were carried out at 295°, 315° and 325°C for 384, 168 and 120 hours, respectively. The diffusion microstructures that developed were examined by optical and scanning electron microscopy (SEM). Concentration profiles were determined using X-ray energy dispersive spectroscopy (XEDS) and electron microprobe analysis (EPMA). The phases observed were the Mg solid solution, Mg₂Zn₁₁, MgZn₂ and Mg₂Zn₃ in all three couples as well as the high temperature, Mg₅₁Zn₂₀ phase in the 325°C couple. The MgZn₂ phase was observed to grow the thickest layer, followed by the Mg₂Zn₃ and the Mg₂Zn₁₁ phases. Parabolic growth constants were determined for each phase. Activation energies for the growth of the intermetallic phases were calculated as 105 kJ/mol for the Mg₂Zn₃ phase and 207 kJ/mol for the MgZn₂ phase.