V. B. Deev

Physical Modifying Effects and Their Influence on the Crystallization of Casting Alloys

Basic theoretical propositions on physical modifying effects (vibration, ultrasonic, electromagnetic agitation, and thermal-temporal processing) on the crystallization of casting alloys are generalized. Mathematical calculations and experimental investigations have revealed that the crystallization and structure formation of casting alloys could be largely determined by the treatment technology using the physical effects during melting and casting. The physical effects on a crystallizing melt cause its strong turbulization and agitation, thereby decreasing the temperature and concentration gradients in the melt, eliminating overheating the liquid phase with respect to the solidus temperature, and breaking off dendrites (which are good crystallization seeds for overall melt volume). The evaluation of the dendrite growth during crystallization showed that splitting the dendrite grains is opposed to their coarsening under physical effects. The physical effects result in bulk crystallization with equiaxed grains without the formation of the columnar structure. The physical modifying effects promote the improvement of the quality of acquired alloys and casts made of them under the conditions of their rational application.

Resource-saving and environment-saving production technologies of secondary aluminum alloys

The main directions of resource-saving and environment-saving fabrication technologies of secondary aluminum alloys in modern industrial conditions are considered. The types of feedstocks and applied smelting aggregates are analyzed, and promising ways to further improve this production process are shown. It is revealed that the traditional processing method of secondary aluminum feedstock, which is widely used in practice, is thermal treatment in a medium of molten chloride salts. Salt-free technologies of processing aluminum dross, which are based on the separation of metal and oxides by the mechanical effect on them under conditions of high temperatures in the medium of the furnace atmosphere or collector metal, are proposed. Their advantages over the widespread salt technology are considered: materials applied to treat the melt are substantially less expensive than alkali metal chlorides; dump slags are environmentally pure; and the process has high productivity since it is performed in one metallurgical aggregate, which excludes the necessity of cleaning the walls and bottom part in it. The examples of implementing the salt-free processing technologies of aluminum feedstock under consideration under conditions of several Russian metallurgical enterprises are shown.

Influence of treatment of melts by electromagnetic acoustic fields on the structure and properties of alloys of the Al–Si system

The influence of treating the melts by electromagnetic acoustic fields on the structure and properties of Al–12% Si and Al–20% Si binary alloys is investigated. In the course of experiments, the frequency of the electromagnetic field induced in the loop antenna varies as 500, 1000, and 2000 kHz. The melts are treated after their degassing and refining. It is established that this treatment method of the melts leads to a reduction of the total preparation time of alloy by 12% on average. The short-term treatment of the melts by electromagnetic acoustic fields promotes the refinement of the main phase components of alloys and an increase in their mechanical properties. When treating the Al–12% Si eutectic alloy with a frequency of 500 kHz, α-Al dendrites are refined from 30 to 22 μm and eutectic Si crystals are refined from 13 to 10 μm. When treating the Al–20%Si eutectic alloy with a frequency of 1000 kHz, eutectic Si crystals diminished from 8 to 5 μm and these of primary Si diminished from 90 to 62 μm. The ultimate tensile strength of the Al–12%Si eutectic alloy increases 13% under the mentioned treatment modes, while the relative elongation increases 17%; as for the Al–20% Si eutectic alloy, the same characteristics increases 9 and 65%, respectively. Based on these investigations, it is concluded that the selection of the treatment parameters of the melts of the Al–Si system by electromagnetic acoustic fields should be determined by the silicon content in the alloy. It is necessary to treat the melt by waves with a higher oscillation frequency with an increase in the silicon concentration. This treatment method makes it possible to form the modified fine-crystalline structure of alloy and, consequently, improves their mechanical properties. It can be successfully used when fabricating fine-crystalline foundry alloys and in the production of alloys of the Al–Si system. To determine the optimal treatment parameters depending on the structure of the initial charge and alloy nature, additional investigations are required.

EFFECT OF ANNEALING ON THE STRUCTURE AND HARDENING OF HEAT-RESISTANT CASTABLE ALUMINUM ALLOY AN2ZhMts

The structure and properties of castable alloy AN2ZhMts of the Al – Ni – Fe – Mn – Zr system based on an (Al) + Al9FeNi eutectic are studied after multistage annealing. The mode of annealing for maximum hardness is determined. The effect of the processes occurring during the annealing on the hardness and electric resistivity is estimated. The properties of alloy AN2ZhMts in annealed condition are compared to those of widely used heat treated copper-free silumins of types AK7ch and AK9ch.

Structure and chemical composition of the AK12MMgN piston alloy fabricated based on various charges

The main requirements for the quality of aluminum alloys of the piston group are considered. The quality of the primary and secondary AK12MMgN alloy fabricated in conditions of various Russian producers is analyzed using the data presented by enterprises interacting with RUSAL in questions of manufacturing this alloy. The main ways to optimize the chemical composition of the AK12MMgN alloy implemented in conditions of OAO RUSAL Novokuznetsk are considered and substantiated and it is shown that other piston alloys with the required level of operational properties can be fabricated based on the AK12MMgN alloy. It is revealed that the quality of the AK12MMgN alloy produced based on the secondary materials under definite manufacturing conditions is no worse that the quality of this alloy produced based on the primary materials. It is noted that, when manufacturing the secondary piston alloys, attention should be paid to their obligatory modification in the liquid state (for example, by phosphorus) in order to approach the microstructure and level of properties in the cast state to alloys produced based on primary aluminum. Recommendations for enterprises, which allow one to produce AK12MMgN alloy with the required structure and chemical composition, are presented.

Investigation into the density of polystyrene foam models when implementing the resource-saving fabrication technology of thin-wall aluminum sheet

The influence of density of polystyrene foam models on the quality of thin-wall casts of the cap of the gas analyzer case made of AK7 alloy smelted based on wastes of home manufacture (the charge contained 50–55% secondary materials) is investigated in conditions of OOO Research-and-Production Enterprise “Vektor Mashinostroeniya” (Novokuznetsk). To foam polystyrene (produced by STYROCHEM, Montreal, Canada) and fabricate the models, a GK-100-3M autoclave is used. Varying temporal-and-time autoclave modes, we acquire different densities of the model ρ = 0.017, 0.019, 0.022, 0.024, and 0.026 g/cm3. Based on the experimental investigations, the values of this index (ρ = 0.022–0.024 g/cm3) at which the model possesses the required surface quality, rigidity, and burnability promoting the minimization of linear defects (mismatch with required geometric sizes, seal, misrun) when fabricating thin-wall casts with specified properties are determined and substantiated.

Boriding of titanium OT4 from powder saturating media

The possibility of application of boriding media based on boron carbide—which additionally contain chromium, titanium, and silicon—for the diffusion hardening of titanium alloys is considered. Boriding in amorphous boron is performed for comparison. The microstructure, elemental composition, and phase composition of diffusion coatings on the OT4 titanium alloy formed by saturation in powder media are investigated. Hardening boride layers are formed on the titanium alloy form saturating media based on amorphous boron and multicomponent mixtures based on boron carbide. In all cases, the phase composition of the coating corresponds to phases TiB, Ti2B5, and Fe2Ti. It is revealed that coatings from 30 to 150 μm thick are formed in conditions of the solid-phase saturation of titanium from powder mixtures due to the diffusion. Temperature-temporal conditions of formation of boride layers on OT4 titanium from powder saturating media are investigated and optimal modes for the formation of operable boride coatings are established. The optimal temperature range for processes of chemical-thermal boriding of titanium (900–1150°C) and saturation time (from 2.5 to 5 h) are determined. The maximal thickness of the operable boride coating on the OT4 titanium alloy is established, being from 180 μm in the case of saturation from Bamorph and up to 240 μm for the 50% B4C + 20% SiC + 25% CrB2 + 5% NaCl mixture at 950°C and saturation time of 4 h. Herewith, it should be noted that it was considered that the largest coating thickness is that retaining on the hardened sample surface.

Influence of melting conditions of aluminum alloys on the properties and quality of castings obtained by lost foam casting

The development of modern foundry production is characterized by a constant increase in requirements for the quality of fabricated casting and rational use of material resources, which determines the search for new technical and process solutions, making it possible to acquire the required properties of cast wares along with resource saving. Herewith, the question of revelation and investigation into the regularities of the influence of thermal-temporal parameters of smelting and pouring of aluminum alloys into the casting mold during the lost foam casting on tightness and mechanical and qualitative characteristics of thin-wall castings remain poorly known and complex for implementation, especially allowing for the performance of resourcesaving measures. In this publication, the influence of process parameters of smelting on the strength, tightness, and content of nonmetallic inclusions in castings of the gas-analyzer case made of AK7 alloy during the lost foam casting is considered. The data set acquired based on the experimental investigations has been subjected to statistical processing. The use of statistic models makes it possible to acquire the results of the influence of the holding time and content of secondary materials in the charge on strength and tightness of mentioned castings. The results of an investigation into the influence of holding the AK7 melt at the overheating temperature of 880–890°С on the content of nonmetallic inclusions in castings show that it can be regulated varying the holding time. This procedure decreases the melt microinhomogeneity and provides the acquisition of numerous castings with a minimal content of nonmetallic inclusions.

Influence of temperatures of melt overheating and pouring on the quality of aluminum alloy lost foam castings

Lost foam casting (LFC) is currently one of the most efficient and promising methods of fabricating high-quality thin-wall castings possessing specified dimensional accuracy, required surface roughness, and other properties. This technology is widely used in the production of aluminum alloy products. To minimize costs in the fabrication of wares and to fabricate high-quality castings, it is reasonable to use an increased amount of secondary materials in the charge, herewith paying attention to the melt overheating temperature and holding time. The results of studying the temperature modes of smelting pouring aluminum alloys in the LFC are presented. The most efficient modes in manufacturing conditions under consideration which provide the best quality characteristics of leak-tight castings by dimensional accuracy and surface roughness were as follows: the melt overheating temperature is 880–890°C and the melt pouring temperature into the casting mold is 820–830°C. The influence of various variants of temperature parameters of smelting and pouring the melt of the AK7 composition during the LFC on the content of nonmetallic inclusions in the cast state is investigated. It is revealed that the minimal γ-Al2O3 content in the final alloy is provided by a melt overheating temperature of up to 880–890 or 940–950°C and a melt pouring temperature into the casting mold of 820–830°C.

Optimization of the composition of silicon brass LTs16K4 with the purpose of increasing its castability when fabricating art castings

Silicon brass of LTs16K4 grade has found wide application in art castings due to its high process properties, beautiful gold-yellow color, and the possibility of deposing various decorative coatings. In this study, the possibility of increasing its fluidity by varying the chemical composition in terms of GOST (State Standard) 17711-93 is investigated. To measure fluidity, the method of vacuum suction is used. This method reveals the change in this characteristic upon adding from 0.1 wt % alloying element (Zn, Si, Al) and shows a high convergence of results. The experimental data are subjected to regression analysis. The quantitative evaluation of the degree of influence of zinc and silicon on the fluidity of silicon brass is found and an adequate mathematical model and the response surface of the fluidity function are constructed. The optimal overheating temperature providing the maximal alloy fluidity upon minimal zinc loss is determined. The results of this study can be used when fabricating art and industrial castings of silicon brass LTs16K4, as well as in other branches of metallurgy and foundry production.