Vliv přípravy lehkých konstrukčních slitin na jejich fázové transformace

• Main Author: Hylský, Josef
• Other Authors: Stulíková, Ivana
• Format: Dissertation
• Language: Czech
• Published: 2010
• Online Access: http://www.nusl.cz/ntk/nusl-286224

A difference in phase transformations in the Mg-Y-Nd-Sc-Mn alloy prepared by two different methods - squeeze casting and powder metallurgy - was studied by relative resistivity changes and hardness measurements. The measurements took place at 77K and at room temperature in the isochronal annealing procedure of 30 řC / 30 min in temperature range of 90 řC - 510 řC. Results achieved in the squeeze cast alloy are in agreement with results of parallel research of microstructure, which proved the existence of thin hexagonal plates up to 390 řC, which are parallel to matrix basal planes. Prismatic plates of the stable phase Mg5(NdxY1-x) developed during annealing melt into solid solution above 390 řC, while particles of the Mn2Sc phase pass even annealing at 510 řC and only coarsen. Previous heating at high temperatures, when solid solution is enriched by Y and Nd atoms, stress precipitation processes, which correspond to precipitation sequence of the Mg-Y-Nd system with two metastable phases and one Mg5(NdxY1-x) equilibrium phase. Only indistinctive resistivity and hardness changes caused by dissolution of thin basal hexagonal plates and by a development of temperature stable Mn2Sc particles are observed during annealing up to 420 řC of the material prepared by powder metallurgy. A dissolution of the equilibrium...