International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

The reversion in magnesium binary alloys with rare-earth metals (Nd, Sm, Y, Gd, Tb, Dy, Ho) at a temperature of 300ºC has been studied. The phenomenon of the reverse dissolution of rare-earth metals in solid magnesium has been established to begin in all alloys under study already after short-term annealing at 300°C for 15 min. As the annealing time at 300°C further increases, the reverse dissolution of rare-earth metals in solid magnesium first continues and then the magnesium solid solution becomes again depleted of rareearth metals because of their precipitation. The degree of reversion has been found to generally increase with an increase in the atomic
number of the yttrium-group rare-earth metal in accordance with its position in the lanthanum row: Gd, Tb, Dy, and Ho. The degree of reversion in the alloys with cerium-group metals (Nd, Sm) with atomic numbers below those of Gd, Tb, Dy, and Ho is substantially smaller than that is in the alloys with yttrium-group metals.

Kinetics of ageing, structure and the strength characteristics of the Mg-Y-Gd-Zr system alloys of compositions near to that of the IMV7-1(~5%Y, ~5%Gd, ~0.5%Zr, remainder Mg) alloy were studied. It was established, that alloying of the Mg-Y-Gd-Zr alloys with Dy, Tb, Sm, Nd results in strengthening of them at room and elevated temperatures both in homogenized and in aged states. Meanwhile, after addition of samarium or neodymium the ageing time needed for substantial strengthening becomes shorter, after addition of terbium it did not change actually and after addition of dysprosium it became longer. Therefore, the strengthening ageing for the Mg-Y-Gd-Zr alloys after addition of Nd, Sm or Dy requires certain corrections.

In the present work, the magnesium alloy WE43 (Mg-Y-Nd-Zr) after high pressure torsion (HPT) was investigated. HPT was conducted at room temperature, 200 °C or 300 °C. As a result of HPT processing, a large number of twins with the twin size of 0.4 − 8.1 µm were formed. Furthermore, the HPT process led to the formation of a very fine grain structure with the average grain size of 30 – 100 nm. The deformation by HPT caused the formation of a displaced basal texture, which sharpens with an increase in the deformation temperature. The refinement of the microstructure brought about an improvement of the microhardness of the alloy over the as-received condition. The microhardness after HPT at the room temperature increased up to 1189 ± 33MPa compared with 774 ± 50 MPa in the initial state. A subsequent aging after HPT led to an additional strengthening to a level of 1411 ± 40 MPa. It was noted that thermal stability of strengthening caused by HPT did not depend on the deformation temperature and sustained up to 250 °C.

In the work effect of the rare-earth metals (REM) on structure of the decomposed Mg supersaturated solid solution after hot deformation was investigated. Investigation indicated Mg solid solution decomposition during hot deformation with precipitation of the RErich particles preferably on the Mg grain boundaries and boundaries between originated blocks. Precipitations on the grain and block boundaries prevent recovery, recrystallization, the grain growth, and increase plasticity of alloys.

The nonequilibrium phase transformation during decomposition of Mg supersaturated solid solutions, containing two rare-earth metals of the different subgroups (cerium and yttrium) are presented and generalized. These processes in the alloys of ternary systems differ from those in the alloys of the adjoining binary systems. They reveal also the similar features in kinetics and the nonequilibrium phase formed during solid solution decomposition