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The recovery (softening) in magnesium alloys with gadolinium (yttrium group REM) and in these alloys additionally alloyed with samarium (cerium group REM) is studied after age hardening and subsequent short-term annealing performed at a slightly higher temperature. The aging-induced hardening is found to decrease at a high annealing temperature, at which the recovery occurs. The recovery of the magnesium–gadolinium alloys decreases with increasing samarium content in them. Small samarium additives are shown to increase the strength properties and, simultaneously, to decrease the recovery of the Mg–Gd alloys during accidental short-term heating when the alloys are used as lightweight structural materials in practice.

The parameters of reversion after hardening aging of magnesium alloys containing two rare earth metals gadolinium (yttrium group) and samarium (cerium group) were determined at various ratios of their contents. The reversion was observed at short annealing at 250 and 300°С beginning with 5 min after preliminary aging at 200°С up to maximum hardening and consisted of significant softening of the alloys then. Measurements of the electrical resistance indicated that during softening the reverse dissolution of the rare earth metals in magnesium-based solid solution takes place with diminution of the quantity of hardening particles precipitated during aging beforehand. The reverse dissolution of the rare earth metals in solid magnesium increases with increase in the annealing temperature after aging from 250 to 300°С and with increase in the gadolinium to samarium ratio in the alloys.

The effect of various heat-treatment conditions on the mechanical properties of Mg–Y–Gd–Zr alloy additionally alloyed with samarium is studied. The alloy is designed in the Baikov Institute of Metallurgy and Materials Science, Russian Academy of Sciences (IMET RAS). Advantages of the new alloy as compared to the available IMV7-1 alloy (of the Mg–Y–Gd–Zr system) are demonstrated, and the optimum heat treatment conditions for the new alloy are determined.

Optical microscopy and hardness measurements are used to study the influence of (Sc + Zr) and (Sc + Hf) transition metal additions and severe plastic deformation by equal-channel angular pressing (ECAP) on the temperature of recrystallization in aluminum Al–Mg2Si alloys. Recovery is revealed to take place in the Al–Mg2Si alloys in the temperature range 200–600°C. Joint scandium and hafnium alloying of the ECAP-deformed alloys weakens softening during recrystallization due to the formation of a structure with grains smaller than those in the structure formed in the alloys free from transition metals.

The phenomenon of post-aging retrogression in magnesium alloys containing two rare-earth metals belonging to different groups, i.e., yttrium Y (the yttrium group) and samarium Sm (the cerium group), is investigated. It is shown that retrogression may occur in alloys with different proportions of yttrium and samarium aged at 200°C for maximum hardness and then annealed at somewhat higher temperatures (250 and 300°C). The process is possible due to decomposition of the supersaturated magnesium solid solution. The degree of the retrogression is shown to depend on the temperature and duration of the post-aging annealing and on the yttrium- to-samarium proportion in the alloys.

The joint effect of samarium and holmium on the properties of an IMV7-1 Mg–Y–Gd–Zr alloy in two different states, namely, homogenized and homogenized and subsequently aged at 200°C to the peak strength, has been studied at testing temperatures of 20 and 250°C. Samarium and holmium do not change the behavior of the Mg–Y–Gd–Zr alloys during aging; at the same time, the presence of ~4% Sm in the alloys accelerates the decomposition of the magnesium solid solution and increases their strength properties, and the presence of 2 to 5% Ho in the IMB7-1 alloys containing 4% Sm leads to a decrease in their strength properties.

The kinetics of decomposition of supersaturated magnesium solid solution and of the accompanying hardening of the latter at 200°C in cast alloy IMV7-1 of the Mg – Y – Gd – Zr system alloyed with two rare-earth metals, i.e., holmium and ytterbium, is studied. Holmium and ytterbium are introduced into IMV7-1 by substituting two other rare-earth metals, i.e., yttrium and gadolinium. It is shown that the presence of holmium and ytterbium instead of yttrium and gadolinium does not change the decomposition behavior of the supersaturated solid solution but decelerates this process and lowers the effect of age hardening.

Metallographic analysis, hardness and electrical resistivity measurements, and tensile tests are used to study the behavior of Al–Mg2Si alloys with (Sc + Zr) transition metal additions during aging performed after preliminary deformation under different conditions. It is shown that the decomposition of the supersaturated solid solution in the Al–Mg2Si alloys with (Sc + Zr) transition metals and without them occurs in the same manner. However, the strength properties of the alloys with transition metals are higher than those of the alloys free from the transition metals because of substantial refining of solid-solution grains and a high density of dispersoid (Sc1 –xZrx)Al3 aluminide particles. A peak hardness is observed for the alloys after quenching, equal channel angular pressing (ECAP), and aging. However, cold rolling after quenching before aging leads to an increase in the strength properties to a greater extent than ECAP performed under the same conditions.

The aging-induced recovery of binary magnesium alloys with various rare-earth metals (Y, Nd, Sm, Gd, Tb, Dy, Ho), in which the decomposition of the supersaturated magnesium solid solution is accompanied by substantial hardening, is studied. It is found that annealing of the alloys at 250°C, which were preliminary aged at 200°C to a peak hardness, leads to their softening; in this case, the hardness continues to decrease as the annealing time increases. Electrical resistivity measurements show that, as a result of annealing at 250°C, recovery takes place and is accompanied by partial dissolution of the decomposition products in the magnesium solid solution; after that, its decomposition continues. The degree of recovery in the alloys with yttrium-group rare-earth metals (Y, Gd, Tb, and Ho) is found to be higher than that for the alloys with cerium-group rare-earth metals (Nd and Sm); within the lanthanide series, the degree of recovery increases with the atomic number of a rare-earth metal.

This article describes the strength properties and microstructure of Al–Mg–Si alloys positioned on a quasi-binary Al–Mg2Si cross section and doped with minor amounts of scandium with zirconium and scandium with hafnium; after quenching, these alloys were exposed to severe plastic deformation and cold rolling with subsequent aging. It was demonstrated that, in the alloys with 1.4% Mg2Si and doped with Sc + Zr and Sc + Hf after equal channel angular extrusion and subsequent cold rolling, the highest strength was that of the alloys doped with scandium with zirconium. The lowest strength was that of the alloys both doped and not doped with scandium, zirconium, and hafnium after equal channel angular extrusion. It has been established that cold rolling of quenched alloys and alloys after equal channel angular extrusion improves strength properties after aging at 170°C in comparison with those aged at the same temperature only after equal channel angular extrusion or only after cold rolling. Analysis of the microstructure has shown that strengthening of the alloys is attributed to slight distortion of the crystalline lattice of aluminum solid solution which is achieved by cold rolling of the alloys aged after equal channel angular extrusion.

The effect of additional alloying of an IMV-7 alloy of the Mg–Y–Gd–Zr system with other rare-earth metals, in particular, cerium and erbium, is studied. The hardness and the electrical resistivity of the alloys, which characterize the kinetics of supersaturated solid solution decomposition upon aging at 200°C, are presented. The hardness and the mechanical properties of the alloys at high temperatures (250, 300°C) are measured. The microstructure of the alloys after heat treatment is examined. Cerium in the content range under study is found to exert no effect on the properties of alloys, such as IMV7-1, whereas erbium is undesirable and can decrease their hardening upon aging.

The aging kinetics, the mechanical properties, and the structure of cast alloy IMV7-1 of the Mg – Y – Gd – Zr system alloyed additionally with dysprosium are studied. It is shown that yttrium and gadolinium may be replaced partially with dysprosium without changes in the aging kinetics and lowering the hardening and the level of the mechanical properties of alloy IMV7-1.

Kinetics and phase transformations are studied for the previously unconsidered decomposition of supersaturated solid solution in magnesium-based alloys Mg–Dy–Sm. The decomposition of solid solution slows when there is an increase in % Dy: % Sm ratio in the alloys. Mg–Sm and Mg–Dy alloys grow harder when Dy and Sm are added to them, respectively. Products of decomposition in ternary Mg–Dy–Sm alloys are the same as in binary alloys Mg–Dy and Mg–Sm but contain combinations of Dy and Sm.

The mechanical properties of as-cast Mg–Dy–Sm alloys additionally alloyed with zirconium to refine grains in the as-cast state have been studied. The dysprosium and samarium contents are close to their mutual solubility in a magnesium-based solid solution at a homogenization temperature of 515°C, and their total content is 4–12 wt %. The mechanical properties of the alloys have been determined in the states homogenized after casting and aged after homogenization. It is found that the strength properties of the alloys increase to σu ≈ 290 MPa and the plasticity decreases to lower values at a relative elongation δ ≈ 3% as the total content of the rare-earth metals in the alloy increases. The Mg–Dy–Sm–Zr alloys are significantly hardened upon aging, and the age hardening effect increases with the rare-earth metal content in them.

The microstructure, the aging kinetics, and the strength properties of Mg–Y–Gd–Zr cast alloys, in particular, a samarium-alloyed IMV7-1 alloy, at room and high (250, 300°C) temperatures after homogenization without and with subsequent aging are studied. Alloying with samarium accelerates the decomposition of the supersaturated magnesium solid solution and enhances the properties of the Mg–Y–Gd–Zr alloys.

The effect of dysprosium added in the amounts such that it does not form an individual phase in equilibrium with solid magnesium on the decomposition of the supersaturated magnesium solid solution in Mg–Sm alloys is studied. The presence of dysprosium in Mg–Sm alloys is found to retard the decomposition of the supersaturated magnesium solid solution and to increase the hardening effect upon aging. When these alloys are aged, dysprosium is partly retained in the magnesium solid solution and partly enters into the compositions of the phases that form during the decomposition of the solid solution and are characteristic of Mg–Sm alloys.

Magnesium-base alloys attract a great attention as light structural materials, where economy of weight is of great importance. According to the last investigations, the highest strength properties of these alloys, can be obtained, when they contain some of the rare-earth metals. All of them belong to the yttrium group. Existence of the rare-earth metals in magnesium alloys enable to form in their structures small hard particles, which increase significantly strength of the alloys. The hard particles appear after the special heat treatments and should have the certain measurements and amounts. In this article the main results of some investigations are described, where the best conditions for the heat treatments of the magnesium alloys with high strength were established. The highest strength in the alloys was observed, when the hard particles were nano-scale in them with certain disposition in the structure.

Constitution of the Mg-rich part of the ternary phase diagram of Mg with two rare-earth metals, Mg-Dy-Sm was experimentally investigated for the first time using optical and scanning electron microscopy (SEM) with electron probe microanalysis (EPMA), x-ray diffraction and differential thermal analysis. In equilibrium with Mg solid solution only two solid phases were found, each of them being the riches by Mg compound in the respective binary systems, Mg24Dy5 and Mg41Sm5. Each of these compounds can also dissolve some other rare-earth metal. There is significant combine solubility of Dy and Sm in Mg solid solution, which decreases with lowering temperature. In the studied part of the Mg-Dy-Sm system one invariant four-phase equilibrium of L + (Mg24Dy5) ⇆ (Mg) + (Mg41Sm5) exists, which takes place at 535 °C. A number of isothermal partial sections and one temperature-composition section of the Mg-Dy-Sm phase diagram were constructed.

The phase compositions of solid Mg–Sm–Dy alloys corresponding to the magnesium-corner region of the phase diagram are studied by optical and scanning electron microscopy, electrical resistivity measurements, and electron microprobe analysis. The obtained results allowed us to determine the joint solubility of samarium and dysprosium in solid magnesium at 500, 400, and 300°C; it decreases with decreasing temperature. The magnesium solid solution is found to be in equilibrium only with the Mg41Sm5 and Mg24Dy5 compounds, which are in equilibrium with the magnesium solid solution in the binary Mg–Sm and Mg–Dy systems.

The joint effect of scandium and zirconium on the strength properties and the electrical resistivity of industrial Al–Mg2Si–based alloys has been studied. The additional alloying of Al–Mg2Si alloys with transition metals leads to substantial grain refinement of the aluminum solid-solution and, therefore, an increase in the strength properties of the industrial alloys.

Metallographic analysis and hardness measurements are used to study the recrystallization processes in aluminum Al–Mg2Si alloys with scandium and combined scandium and zirconium additions that occur during annealing of the cold-deformed alloys at 100–600°C. The temperature of the onset of recrystallization of the Al–Mg2Si alloys with scandium and combined zirconium and scandium additions is shown to be 50°C higher than that of the alloys free from scandium and zirconium. It was noted that the small grain sizes of the alloyed compositions lead to weaker disordering during recovery and recrystallization.

Multiaxial deformation (MAD) of an Mg-0.3% Ca alloy is performed when temperature decreases within the ranges 425–375 and 400–325°C. A decrease in the temperature at the end of MAD causes a decrease in the grain size from 7–8 to 0.5–2 μm and the spread of a sharp prismatic texture, which determine a high strength (σu = 194 MPa) and plasticity (δ = 39%). After MAD in the range 425–375°C, the Mg-0.3% Ca alloy is subjected to equal-channel angular pressing (ECAP) at temperatures of 275 and 325°C. ECAP causes a decrease in the grain size from 7–8 μm to 2 and 5 μm, respectively. The texture also changes from prismatic to tilted basal texture. This results in an increase in the strength to 170-160 MPa at plasticity δ = 25–30%. It is shown that MAD can be used as both final and preliminary processing before ECAP to form an ultrafine-grained structure in the Mg-0.3% Ca alloy.

Differential thermal and metallographic analyses are used to study the alloys lying on the sections of the phase diagram opposite to the Al corner and passing across the binary alloy compositions Al-2.5% Sc-Al-7% Si and Al-5% Sc-Al-14% Si. These results are used to plot two vertical sections and part of the liquids surface of the Al-Sc-Si phase diagram from the Al corner to 5% Sc and 14% Si. The character and temperatures of invariant equilibria in aluminum-rich alloys of the Al-Sc-Si system are determined.

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.

The effect of severe plastic deformation and subsequent aging on the structure and properties of cast and hardened magnesium alloys containing samarium and yttrium is studied. Severe plastic deformation leads to additional hardening both before and after aging. Hardening is achieved by the formation of nanocrystalline structure in quenched alloys or submicrocrystalline structure in cast alloys. Severe plastic deformation results in the rapid decomposition of a supersaturated magnesium solid solution and additional hardening due to the formation of nano-sized particles of hardening phases.

Metallography and electrical resistivity and hardness measurements are used to study the aging and recrystallization of Al-rich Al-Sc-Cr-Zr alloys with 0.1–0.4% Sc, 1.0% Cr, and 0.2% Zr. During aging at 350°C, the hardness of the alloys is found to increase substantially even after 0.5-h aging as compared to that of the deformed state. Variations of the hardness and electrical resistivity of all alloys exhibit similar behavior; however, the higher the scandium content in the alloys, the higher the strengthening effect reached after aging for 2–4 h. Combined small scandium, chromium, and zirconium additions to aluminum are shown to increase its recrystallization temperature; therewith, the effect of scandium on the increase in the temperatures of the onset and finish of recrystallization is more substantial.

The phase composition and recrystallization of Al-based alloys with small amounts (up to 4 wt %) of transition metals, such as Sc, Mn, and Zr, are studied by metallography and electrical resistivity and hardness measurements. No new phases, besides phases in equilibrium with an Al-based solid solution in the associated ternary systems, are found for the portion of the quaternary Al-Sc-Mn-Zr system under study. It is also found that the manganese and zirconium solubilities in the Al-based solid solution decrease in the presence of scandium and that zirconium additions in Al-Sc-Mn alloys increase their recrystallization temperature.

The effect of annealing at 100-400°C on strengthening of ageing alloys of the Mg-Sm system subjected to rapid plastic deformation by torsion under pressure is studied. With the annealing temperature elevated to 200-250°C strengthening, caused by rapid plastic deformation, is retained, but it decreases with a further increase in temperature.

Mg - Al - Ca alloys positioned in the Mg - Al 2 Ca quasi-binary section are studied. It is shown that alloys of this system bearing the Al 2 Ca compound as a hardening phase can be used for developing structural alloys with elevated strength at 170°C and that the strength characteristics of the Mg - Al - Ca alloys can be improved by adding manganese.

The joint effect of manganese and chromium additions (0.25–0.8 wt %) on the recrystallization of Al-(0.1–0.4 wt %) Sc alloys is studied. The recrystallization is studied using changes in the microstructure of the alloys annealed in the temperature range 100–630°C. Depending on the scandium content in the alloys, combined alloying of them with manganese and chromium is found to lead to a slight increase or decrease in the recrystallization temperature of the Al-Sc alloys.

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.

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.

The effect of severe plastic deformation by high-pressure torsion on the structure and properties of aged magnesium alloys containing 2.8–5.5 wt % Sm (the maximum solubility of samarium in solid magnesium is 5.8 wt %) are studied. The severe plastic deformation leads to substantial strengthening caused by the formation of a submicrocrystalline structure along with strengthening caused by the decomposition of a supersaturated magnesium-based solid solution.

The decomposition at 250 °C of the Mg supersaturated solid solution in the ternary Mg–Nd–Y system and in binary Mg–Nd and Mg–Y alloys was studied. The kinetics of precipitation in ternary Mg–Nd–Y alloys differs from the kinetics of precipitation in binary Mg–Nd and Mg–Y alloys. Precipitates with the same crystal structure form in a shorter ageing time in ternary Mg–Nd–Y alloys than in binary Mg–Y alloys. The change of volume and the kinetics of solid solution decomposition in the ternary Mg–Nd–Y alloys as compared with the binary ones suggest that there is a certain solubility of Y in the Nd-rich precipitates and of Nd in the Y-rich precipitates.

The structure and properties of a magnesium alloy of theMg – Y – Gd – Zr system are studied. The kinetics of decomposition of the magnesium-base supersaturated solid solution is studied at 175, 200, 225, and 250°C and the mechanical properties of the alloy are determined at room and elevated (to 350°C) temperatures. A hot-pressed plate after aging for maximum hardening of the alloy exhibits high strength parameters both at room and elevated (to 300°C) temperatures.