T. V. Dobatkina

Solid-state phase equilibria in the Mg corner of the MgGdSm phase diagram

Abstract The solid-state phase equilibria in the Mg corner of the MgGdSm phase diagram were investigated by optical and scanning electron microscopy, X-ray diffraction and electrical resistivity measurements. The experiments showed that in the Mg corner of the system there are only three solid phases in equilibrium: the Mg solid solution and the two Mg-richest compounds of the adjoining binary systems. Each of the binary compounds take into solution significant quantities of the second rare-earth metal. Gd and Sm mutually reduce their solubility in the Mg solid solution. Isothermal sections of the phase diagram at 500 and 300°C are presented.

Phase equilibria in solid Mg-Rich Mg-Sm-Tb alloys

The structure of Mg-rich Mg-Sm-Tb alloys with samarium and terbium contents up to 30 at % each is studied by metallography, electron microprobe analysis, and electrical resistivity measurements. The magnesium-based solid solution is found to be in equilibrium only with the Mg41Sm5 and Mg24Tb5 phases belonging to the Mg-Sm and Mg-Tb binary systems composing the ternary system, respectively. The individual and total samarium and terbium solubilities in a magnesium-based solid solution at 500 and 300°C are determined. The terbium and samarium solubilities in the Mg41Sm5 and Mg24Tb5 phases, respectively, are also determined. Partial isothermal sections at 500 and 300°C of the Mg-Sm-Tb phase diagram in the Mg- rich region are constructed.

Effect of yttrium and chromium on the recrystallization of Al-Sc alloys

The effect of small chromium and yttrium additions (0.14–1.0 wt%) on the recrystallization of Al-Sc alloys having 0.1–0.4% Sc is studied with polarized light. The microstructure of cold-rolled samples annealed at 100–630°C for 1 h is examined. The chromium and yttrium additions are found to slightly affect the recrystallization temperature of the Al-Sc alloys: they increase or decrease it slightly depending on the scandium content.

Phase equilibria in Al-rich Al-Sc-Cr alloys

Phase equilibria in aluminum alloys containing up to 1.2 wt % Sc and 1.0 wt % Cr are studied by optical microscopy and differential thermal and electron microprobe analyses. Two vertical sections and the projection of liquidus surface have been constructed. The four-phase nonvariant equilibrium at a temperature of 656.5 ± 1°C is found to have a transition character. The Al-based solid solution is found to be in equilibrium only with the Al3Sc and Al7Cr binary phases.

Al-rich portion of the Al-Hf phase diagram

Electrical resistivity measurements, differential thermal analysis, optical microscopy, and the deposition of hafnium compound particles from a melt are used to study the Al-rich portion of the Al-Hf phase diagram. Prominence is given to the hafnium solubility in solid and liquid aluminum. The studies show a peritectic character of the invariant reaction during the solidification of alloys with sufficiently high hafnium contents and a slight difference between the peritectic and melting temperatures of pure aluminum. The hafnium solubility in solid and liquid aluminum is shown to increase with the temperature. The hafnium solubility in solid aluminum at the peritectic temperature (maximum solubility) is 1.00 wt % (0.153 at %); the hafnium solubility in liquid aluminum at this temperature is 0.43 wt % (0.065 at %).

Study of the phase equilibria and the decomposition of a supersaturated solid solution in magnesium alloys with aluminum, calcium, and manganese

Magnesium alloys Mg-Al-Ca-Mn having 1 wt % Al, up to 1.8 wt % Mn, and up to 1.6 wt % Ca are studied by optical microscopy, electron microprobe analysis, and electrical resistivity and microhardness measurements. The phase equilibria corresponding to the Al, Ca, and Mn concentration ranges under study were determined and sections of the isothermal tetrahedrons of the Mg-Al-Ca-Mn phase diagram in the Mn-rich region at 450 and 300°C have been constructed. As was found, manganese does not affect the decomposition kinetics of the magnesium supersaturated solid solution in ternary Mg-Al-Ca alloys but increases their hardness.

Effect of Cerium and Yttrium on Aging Processes in Alloys of the Al – Mg System

The effect of small additives of rare earth metals (REM) (cerium and yttrium in an amount of about 0.6 wt.% each) on the decomposition of supersaturated solid solution of magnesium in aluminum in Al – Mg alloys bearing up to 16.6% Mg is studied in the process of natural and artificial aging. It is shown that the addition of REM delays the decomposition of the aluminum solid solution.

Study of the decomposition of the magnesium-based solid solutions in Mg-Sm-Tb alloys

Kinetics and structural transformations upon the decomposition of a magnesium-based supersaturated solid solution in Mg-Sm-Tb alloys have been studied at various relations between the concentrations of terbium and samarium. It has been established that with increasing terbium content in the alloys the strengthening upon the decomposition of the supersaturated magnesium-based solid solution increases. The decomposition of the supersaturated magnesium-based solid solution in the Mg-Sm-Tb alloys with a percentage ratio (wt %) Tb: Sm of about 2.5 exhibits signs characteristic of the decomposition of the supersaturated solid solution in binary Mg-Tb alloys. With allowance for the equilibrium Mg-Sm-Tb phase diagram, this gives grounds to suppose that samarium is mainly dissolved in the products of the decomposition of the magnesium solid solution that are characteristic of Mg-Tb alloys.

Behavior of the high-strength magnesium alloy IMV7-1 of a Mg-Y-Gd-Zr system in annealing

The changes in the structure and properties of the high-strength magnesium alloy IMV7-1 of a Mg-Y-Gd-Zr system are studied after heating at various temperatures. The alloy is hot-worked before annealing to obtain wrought semifinished products. The high stability of a hot-worked structure in annealing is established. It indicates the possibility of using the alloy as a light structural material at elevated (up to 300°C) temperatures. As the annealing temperature increases to 400°C and the holding time is one or two hours, there is only a slight decrease in the hardness, characterizing the strength properties of the alloy. With a further increase in the annealing temperature, a sharp fall in the hardness is observed. Investigation of the structure shows recrystallization in the alloy after annealing at temperatures up to 400°C. After annealing at higher temperatures of 450 and 500°C, the abrupt fall in the hardness is accompanied by complete disappearance of the elongated deformed grains which exist in the hot-worked state and by a significant grain growth. After recrystallization, the alloy retains the ability to be significantly strengthened upon aging, resulting in decomposition of the magnesium-based supersaturated solid solution.

Section of the isothermal tetrahedron of the Al-Cu-Mg-Zr phase diagram at 490°C

The phase equilibria in the Al-Cu-Mg-Zr system at 490°C have been studied for Al-rich alloys with 0.3% Zr and from 0 to 10% Cu or Mg. The (Al) solid solution is found to be in equilibrium with only binary θ(CuAl2) and ZrAl3 and ternary S (CuMgAl2) phases of the ternary Al-Cu-Mg system. The section of the isothermal tetrahedron of the Al-Cu-Mg-Zr phase diagram at 490°C, which corresponds to 0.3% Zr and up to 10% Cu or Mg, is constructed.