Thermal development of microstructure and precipitation effects in Mg-10wt%Gd alloy

Thermal effects on the microstructure and precipitation in Mg-10wt%Gd alloy were studied in this work. The role of lattice defects was investigated using positron annihilation spectroscopy. Studies of defects by positron annihilation were combined with X-ray diffraction and microhardness measurements. Vacancies bound to Gd atoms were found in the homogenised sample quenched down to room temperature. Subsequently, clustering of Gd atoms takes place with increasing temperature. The Gd-rich clusters represent precursors for further precipitates of the beta" phase. The formation of fine beta" phase particles leads to a maximum in the hardness. Vacancy-like misfit defects are introduced by precipitation of beta' phase particles in the sample annealed to higher temperatures. A good correlation between the intensity of trapped positrons and the contribution by positrons annihilating Gd electrons was found.