INTERMETALLIC PHASE FORMATION AND GROWTH IN THE MG-Y SYSTEM

摘要

Rare earths have been added to magnesium alloys in order to improve the creep resistance, corrosion resistance and strength. Solid-to-solid diffusion couples were assembled between Mg (99.9%) and Y (99.9%) to investigate the formation and growth of intermetallic phases and interdiffusion in the Mg-Y system. The diffusion anneals were performed at 450, 500 and 550°C for 360, 240 and 120 hours, respectively. The intermetallic layers that developed were the δ-Mg_2Y and ε-Mg_(24)Y_5 phases, however the MgY phase did not form. A substantial penetration of Y in Mg was observed, however along with Kirkendall porosity that indicates faster diffusion of Mg than Y in Mg solid solution. The activation energies for parabolic growth in ε-Mg_(24)Y_5 and δ-Mg_2Y were calculated to be 84 kJ/mol and 77 kJ/mol, respectively.