Vol 59, No 2 (2018)

Rolling and perpendicular to rolling surfaces of AlCu₆Si aluminum sheet have been anodized at 27 ± 1°C in 20 wt % sulfuric acid containing an additive of white sugar powder with and without permanent weak magnetic field. After one hour of anodizing, some hillocks-shaped micropores are developed and craters are formed in the oxide layers. The micropores obtained in rolling faces are often smaller than those obtained on other faces. Sulfuric anodizing at 21 V causes the formation of combined micropore-nanopore structures in rolling surface. It demonstrated that sugar additive increases the density of micropores in spherical shape in rolling surface and the increasing of sugar concentration changes the pores to hillocks form. In addition, the application of weak magnetic field induces homogeneous repartition of micropores.

The highly-alkaline red mud, which is the Bayer process residue generated from the alumina industry, is a severe environmental problem. In this study, a new calcification–carbonation process was proposed for red mud disposal. Red mud was processed by lime to convert the aqueous silicon phase into hydrogarnet, which was then decomposed by CO₂ to recover alumina. In the direct carbonation process, the NaOH-containing solution after calcification was directly carbonated without prior liquid–solid separation. The discrete and direct carbonation processes had alumina recovery rates of 34.9 and 35.5%, respectively, with 0.15 and 0.21 wt % Na₂O in the final red muds, respectively. The optimum NaOH concentration in the calcification liquor was 30 g/L. Under these conditions, alumina recovery was increased to 44.5% and the Na₂O concentration in the processed red mud was reduced to <1 wt %. The final red mud can be used as a construction material.

The statistical dependences of the mechanical properties of 218 forgings (15 dimension types) made of VT3-1 and VT6 alloys in 2000–2014 on the chemical composition (content of alloying elements and impurities and structural and strength aluminum and molybdenum equivalents), type, subtype, and structural parameters after annealing, quenching, and aging are investigated. It is established that the strength and plastic properties of single-type forgings vary rather widely. The part of the variation in the forging properties caused by fluctuations of the content of major components and impurities, as well as by the influence of the structural type and sizes of structural components, is evaluated. It is revealed based on correlation analysis that the variation in amounts of each alloying element and impurity has little or no effect on the forging properties. This is caused by small fluctuation intervals of their concentrations in the limits of the grade composition. However, their total content expressed through aluminum and molybdenum equivalents can vary in a rather wide range. It is statistically substantiated that the part of the variation in the tensile strength of forgings of VT3-1 and VT6 alloys caused by the influence of the chemical composition (recalculated to aluminum and molybdenum equivalents) may be ∼25–65%, while that caused by the influence of the structural type and subtype is about 20%. The part of the variation under the joint effect of these two factors (composition + structure) can reach ∼50–65%. This index for plasticity and impact toughness is smaller and lies in a range of 20–35%. Mathematical models for forecasting the mechanical properties of forgings depending on the structural parameters and aluminum and molybdenum equivalents are proposed.

Rheological properties of the EP742-ID alloy are investigated during high-temperature compression tests of cylindrical samples with various ratios of homological initial sizes of diameter and height (d₀/h₀). It is shown by the results of tests in ranges of temperature t = 1000–1150°C and initial deformation rates ε̇₀= 3 × 10^–2–3 × 10^–4 s^–1 that an increase in the compression flow tension manifests itself at all temperatures and deformation rates with an increase in ratio d₀/h₀ with the linear dependence on the magnitude of ε̇₀ and ratio d₀/h₀. The procedure of recalculating characteristics of the deformation resistance for the specified ratio of homological parameters is proposed. An increase in the compression flow tension is associated with an increase in the rigidity coefficient of the samples and their specific contact surfaces. The temperature dependence of the apparent activation energy of the plastic deformation (Q_def) of the alloy and its relation with the phase composition and running conditions of the dynamic recrystallization of the γ-solid solution are established. The magnitude of Q_def in temperature conditions of the development onset of the dynamic recrystallization of the γ-solid solution (1000–1050°C) is 959 kJ/mol for samples with d₀/h₀ = 0.75. The largest values of Q_def for the samples with d₀/h₀ = 0.75 equal to 1248 and 1790 kJ/mol are observed in a temperature region of the intense dissolution and coagulation of the grain-boundary γ′-phase (1050–1100°C). The value of Q_def for the samples with d₀/h₀ = 3.0 increases to 2277 kJ/mol in this temperature range. The apparent activation energy of the plastic deformation lowers to 869 kJ/mol in the temperature region of the γ-solid solution with grain-boundary primary and secondary carbides (1100–1150°C). The results of compression of alloy samples during single and repeated sequential loading with various durations of pauses between deformation actions are presented. It is shown that no metadynamic recrystallization occurs in the experimental conditions in the γ + γ′-region, while it runs slowly in the γ-region.

The possibilities and efficiency of applying the thermohydrogen processing (THP) of the high-modulus Ti–8.7Al–1.5Zr–2.0Mo titanium alloy with an aluminum content exceeding the solubility limit in α-titanium are considered. Experimental data on the influence of hydrogen on the alloy phase composition and structure are acquired. Regularities of phase transformations in the hydrogen-containing alloy under various thermal impacts are analyzed. The phase diagram of the alloy–hydrogen system in the hydrogen concentration range from the initial one to 1.0 wt % and the temperature range from 20 to 1100°C is constructed. It is shown that a single-phased β-structure is fixed with the concentration of introduced hydrogen of 0.6 wt % and higher by means of quenching from the β-region. Hydrogen saturation up to 0.8–1.0% leads to the implementation of the β → δ shear hydride transformation during quenching from temperatures below 750°C, and to the partial eutectoid transformation of the β-phase under slow cooling. It is established that hydrogen extends the stability region of the β-phase, lowering the temperature of the β/(α + β) transition by 210°C (at 1.0% H), and increases the stability temperature of the α₂-phase by 50°C. The process flowsheets and THP modes forming two structural types—submicrocrystalline and bimodal—are developed and approved for alloy samples. The formation mechanisms of these structures during THP are analyzed and the mechanical properties of the alloy are determined. It is established that THP leads to an increase in strength and hardness when compared with the initial state. The THP forming the microcrystalline structure causes a decrease in plasticity characteristics at the maximal hardness.

Al–Cu–Mn (Zr) aluminum alloys possess high strength and manufacturability without operations of thermal treatment (TT). In order to investigate the fabrication possibility of the aluminum boron-containing alloy in the form of sheet rolling with an increased strength without TT, Al–2% Cu–1.5% Mn–2% B and Al–2% Cu–1.5% Mn–0.4% Zr–2% B alloys are prepared. To exclude the precipitation of refractory boride particles, smelting is performed in a RELTEK induction furnace providing intense melt stirring. The smelting temperature is 950–1000°C. Pouring is performed into graphite molds 40 × 120 × 200 mm in size. It is established using computational methods (Thermo-Calc) that manganese forms complex borides with aluminum and zirconium at the smelting temperature; herewith, a sufficient amount of manganese remains in liquid, while zirconium is almost absent. The formation of AlB₂Mn₂ complex boride is proven; however, the amount of manganese remaining in the solid solution is sufficient to form the particles of the Al₂₀Cu₂Mn₃ phase in amounts of up to 7 wt %. Boron stimulates the isolation of Al₃Zr primary crystals in the alloy with zirconium; in connection with this, an amount of zirconium insufficient for hardening remains in the aluminum solid solution. The possibility of fabricating thin-sheet rolling with a thickness smaller than 0.3 mm with homogeneously distributed accumulations of the boride phase with a particle size smaller than 10 μm is shown. A high strength level (up to 543 MPa) is attained without using quenching and aging due to the precipitation of dispersoids of the Al₂₀Cu₂Mn₃ phase during hot deformation (t = 450°C).

Al 6061_100–x–x wt % B₄C (x = 0, 5, 10, 20, 30 and 40) composites, prepared by mechanical alloying and compacted at room temperature, have been used for the present investigation. The effects of B₄C content and milling time on the powder morphology, powder particle size, and other powder characteristics such as the apparent density, tap density, flow rate, cohesiveness, and hausner ratio are systematically investigated. The steady state of milling process is determined by observing the correlation between apparent densities and milling time explained by the morphological evolution of the powder particles during the milling process. The Hausner ratio (HR), estimated to evaluate friction between the particles, decreases with an increase in milling duration and B₄C content due to the changes in morphology and hardness of the powders. The compressibility behavior of post-compacts as a function of compaction pressure and the B₄C content was analyzed by using several linear and non-linear powder compaction equations. The linear Panelli and Ambrozio Filho, and non-linear Van Der Zwan and Siskens equations give the highest regression coefficients. The results are explained in terms of the plastic deformation capacity and plastic deformation coefficient of the powders, which are influenced by the hardness and the morphology of the powder. After compaction, the supersolidus liquid phase sintering was performed at various temperatures (585, 610 and 630°C) under high purity nitrogen atmosphere. The results revealed that the sinterability was degraded by increasing the reinforcement content, particularly above 10 wt % B₄C. Neutron radiography measurements conducted on the rolled composite sheet have revealed the uniform distribution of B₄C particles in the composite.