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To obtain better comprehensive properties of cast Al-Cu-Mg alloys, the secondary aging (T6I6) process (including initial aging, interrupted aging and re-aging stages) was optimized by an orthogonal method. The microstructures of the optimized Al-Cu-Mg alloy were observed by means of scanning electron microscopy and transmission electron microscopy, and the properties were investigated by hardness measurements, tensile tests, exfoliation corrosion tests, and intergranular corrosion tests. Results show that the S phase and θ' phase simultaneously exist in the T6I6 treated alloy. Appropriately increasing the temperature of the interrupted aging in the T6I6 process can improve the mechanical properties and corrosion resistance of Al-Cu-Mg alloy. The optimal comprehensive properties (tensile strength of 443.6 MPa, hardness of 161.6 HV) of the alloy are obtained by initial aging at 180 °C for 2 h, interrupted aging at 90 °C for 30 min, and re-aging at 170 °C for 4 h. [ABSTRACT FROM AUTHOR]

The synergistic effects of 0-0.3 wt.% Sc addition and retrogression and re-aging (RRA) on microstructure and mechanical properties were evaluated in Al-8.0Zn-2Mg-2Cu-0.15Zr alloy. The minor Sc addition can effectively refine the grains of the tested alloy. When the Sc content increased from 0 to 0.2 wt.%, the grain size decreased from 200-250 to 30 μm. As the Sc content increased from 0.2 to 0.3 wt.%, the grain size was still 30 μm, almost without change. The grain refining is due to the formation of Al3(Sc, Zr), which has a better coherent relationship with the matrix than Al3Zr. The RRA treatment results in a slight decrease in the tensile strength (Rm) and significant improvement in the total elongation (A) of the tested alloy. The sample's Rm before and after the RRA decreased slightly from 517 to 510 MPa when the Sc is 0.3 wt.%; the A increased significantly from 6.0 to 12.0%. The tested alloy prepared by adding 0.1-0.3 wt.% Sc has a higher tensile strength and toughness than those alloys without Sc due to the formation of Al3(Sc, Zr). After the RRA treatment, both the formation of η (MgZn2) and the release of internal stress decrease the strength and increase the total elongation of the tested alloy relative to values before the RRA treatment. [ABSTRACT FROM AUTHOR]

The effects of different Si and Cr contents on the microstructure and mechanical properties of new type aluminum alloy with low silicon content were studied by means of hardness test, tensile test and metallographic preparation, SEM, EDS and DSC. The results showed that when the Si content increased gradually, the hardness and tensile strength increased first and then decreased. When the Si content was 3.5%, the hardness and tensile strength reached the maximum. The microstructure observation showed that when the Si content was 3.5%, the microstructure was the most fine and dense, and the secondary dendrite arm spacing (SDAS) of the alloy had the minimum value. When the content of Cr element increased gradually, the tensile strength and elongation showed a trend of increasing gradually, and the maximum value was obtained at 0.5%. When Si was 3.5% and Cr was 0.5%, the best mechanical properties were obtained. At this time, the microstructure of the alloy was fine, dense and uniform, and Mg2Si strengthening phase was precipitated during heat treatment. Cr element has the functions of solid solution, fine crystal and dispersion strengthening. Therefore, the tensile strength, yield strength and elongation of the new aluminum alloy were 350.7 MPa, 303.0 MPa and 8.56%, which has obvious advantages over the traditional cast Al-Si alloy. [ABSTRACT FROM AUTHOR]

In this paper, 7050-T6 high-strength aluminum alloy with 3-mm-thickness is taken as the research object, and it is welded by CMT Advanced 4000R NC welding system. The microstructure, mechanical properties, evolution of joint phase and fatigue properties are studied, and the tensile and fatigue fracture are observed and analyzed. It is found that the fusion zone is dominated by columnar crystal structure and typical epitaxial solidification; the structure of weld zone is mainly equiaxed crystal and dendrite. After 360 h of natural aging, the hardness distribution of the joint is not uniform, and the hardness of the weld zone is the smallest. The hardness of the overaging softening zone is 10 HV lower than that of the solid solution zone, and a softening zone with a width of about 5 mm appears in the joint. The HAZ softens obviously, and the fracture surface shows typical dimple fracture morphology. The results show that the conditional fatigue limits of the specimens are 166.4 and 109.3 MPa respectively under the condition of setting Nf = 107 fatigue cycle. The fatigue initiation area of the joint is mainly welding porosity, and the fatigue striation spacing of the extension area is different. In the process of crack propagation, the striation tends to bypass the second phase particles; The instantaneous fracture area consists of dimples of different sizes. The thermal simulation test of the weld is carried out through the moving Gaussian heat source model in ANSYS software. In addition to the plate-like Mg2Si phase observed in the weld, FeAl3 and (FeMn)Al6 impurity phases are also found, only a weak diffraction peak of MgZn2 phase is found in the solid solution zone. The microstructure evolution of HAZ is analyzed by HRTEM images. It is found that there are tiny GP zone precipitates in the solution zone. [ABSTRACT FROM AUTHOR]

The authors have analyzed the necessity to improve the composition of existing critical structural materials for the purpose of developing metal matrix materials, which combine a highly plastic metal base and high-melting, high-strength, high-modulus fillers. Dispersed yttrium oxide (Y2O3) particles are preferred for iron matrix alloys, because of their stability at pyrometallurgical process temperatures and inertness to alloy components. The manufacturing of new materials by addition of dispersed particles into a liquid melt during casting using a centrifugal casting machine to obtain a hollow (pipe) billet is considered. The potential for improving the mechanical and operational properties of metal matrix materials in comparison with the monomaterial is demonstrated. This paper describes the thermodynamic modeling of high-temperature processes in the yttrium oxide–metal matrix (melt) system. The modeling has been carried out using the FactSage software package. A composition corresponding to 12Cr18Ni10Ti (12Kh18N10T) steel was used to model the matrix material. The calculations have been based on the ratio of 1 g of yttrium oxide additive per 100 g of matrix metal melt. It can be concluded based on the modeling results that the added dispersed yttrium oxide powder does not interact with alloy components, does not dissociate, and does not undergo allotropic transformations. The experiments on production of centrifugal castings using yttrium oxide as a strengthening phase with the aim of increasing radiation resistance have been proved to be expedient. The developmental focus of the most effective technology for creating metallic materials based on iron matrix dispersed-hardened with yttrium oxide has been established. [ABSTRACT FROM AUTHOR]

NiCrAlY coatings were fabricated by atmospheric plasma spraying. The influence of the heat treatment on the corrosion–wear behavior of the coatings in artificial seawater was investigated. The microstructure of the coatings became denser and more homogeneous after the heat treatment. After heat treatment at 1100 °C, the coating had the fewest pores and cracks and the oxide dispersive strengthening phase of Y2O3 was clearly increased to form a layer approximately 10 nm thick and uniformly distributed in the matrix. The heat treatment effectively improved the microhardness and corrosion–wear properties of the coatings. This coating had the highest microhardness of 371.1 HV, the lowest friction coefficient, and a wear rate of 0.24 and 1.01 × 10−6 mm3/Nm and the lowest corrosion rate after heat treatment at 1100 °C, giving it excellent corrosion–wear properties. [ABSTRACT FROM AUTHOR]

It is established that intercrystallite corrosion of cutting-ceramic inserts arises when the chromium content in the peripheral zone of the grains is depleted by the deposition of chromium carbides at the grain boundaries, in the presence of stress due to the fast cooling of the inserts from high temperatures. This is especially apparent when 12Kh18N10Т, 40Kh13, 14Kh17N2, and other steels that are hard to machine are worked by a tool equipped with inserts of VOK-60M modified cutting ceramic. Research shows that the intercrystallite corrosion of cutting-ceramic inserts may be attributed to the stress arising in the surface layers of the grains as a result of carbide or nitride deposition. Heating cutting-ceramic inserts at 650–800°С lowers this stress and restores their resistance to intercrystallite corrosion. Research also shows that chromomanganese cutting-ceramic inserts are less susceptible to intercrystallite corrosion than are chromium–manganese–nickel inserts, while chromium–manganese–nickel cutting-ceramic inserts are less susceptible than are chromonickel inserts. The benefits of chromium–manganese–nickel cutting-ceramic inserts are especially pronounced with relatively brief machining of 12Kh18N10Т, 40Kh13, 14Kh17N2, and other such steels, in rigorous conditions, with a temperature of 600–650°С in the workpiece–tool contact zone. A new theory of the intercrystallite corrosion of VOK-60M modified cutting ceramic is based on the role of the kinetic factor at the relatively low tempering temperatures associated with the deposition of metastable carbide, although this does not lead to maximum change in free energy of the system but only to a relative change. In the cutting ceramic, this carbide may be chromium carbide (Cr, Тi)23C6, which is greatly enriched with titanium. With increase in tempering temperature, the deposited carbide tends toward the stable composition Cr23С6. Prolonged holding at the tempering temperature also tends to favor thermodynamic equilibrium. In other word, the chromium carbide is gradually enriched to reach the stable composition Cr23С6. This process is more rapid at higher temperatures. Obviously, the variation in composition of the carbide deposited at the grain boundaries in VOK-60M cutting ceramic with change in temperature and holding time will affect the kinetics of electrochemical solution of the system consisting of the carbide in contact with a solid solution. Research shows that vacuum sintering and annealing markedly improve the thermal stability. For the cutting ceramic, this is explained not only by the removal of fusible impurities but also by the larger quantity of aluminum and other alloying elements that remain in the strengthening phase, rather than being bound in oxides. Sintering in vacuum ensures greater plasticity of cutting ceramic based on nickel and cobalt in cutting 12Kh18N10Т and 14Kh17N2 steel at high speeds, with high temperatures in the machining zone. In addition, on sintering in vacuum furnaces, the content of small nonmetallic inclusions in the basic structure is 5–7 times less than in regular cutting ceramic. That significantly improves the deformability of the ceramic inserts. [ABSTRACT FROM AUTHOR]

Currently, critical components and assemblies made of traditional materials do not always meet the increased requirements of designers and service conditions. One solution to this problem is the development and application of dispersion-strengthened metal matrix composites. According to the informational–analytical review, a new fabrication technology of aluminum-based dispersion-strengthened composite material is presented. The peculiarities of this technology are described and sample macro- and microstructures, as well as mechanical characteristics of as-cast samples, are presented. The synthesis of strengthening particles immediately in the melt makes it possible to fabricate composites in one stage and provide thermodynamic stability, dense contact, and good adhesion between the matrix and strengthening phase. The particle sizes of the solid phase are in a range from 3 μm to 2 mm. The structural-and-phase state of the produced material is studied using optical metallography and X-ray diffraction analysis (a DRON-2 diffractometer). The microstructure is studied using a Keyence VHX-1000 microscope. The sample hardness is determined using a TKS-1M device, microhardness is determined using PMT-3 and HMV Shimadzu devices, ultimate strength is determined using ZD 10/90 and UME-10TM universal tensile testers, and impact strength is determined using an MK-30a pendulum impact tester. It is found that the variation in size and content of the strengthening phase makes it possible to vary mechanical properties of cast metal in a wide range. The application of the proposed technology will substantially decrease temporal and economical costs. A decrease in the fabrication cost of the dispersion-strengthened composite material is expected according to the results of the evaluative calculation. [ABSTRACT FROM AUTHOR]

Abstract—The intermetallic Ti3Al based alloys with the strengthening boride phases were obtained by the powder metallurgy methods; their composition, structure, and properties were studied. The optimum conditions for thermal treatment allowing obtaining the composite materials of the specified composition with the inclusions of the MAX phase were determined. [ABSTRACT FROM AUTHOR]

Features of the effect of alloying elements on linear thermal expansion coefficient of wrought heat-resistant alloys based on the Ni–Fe system are studied. Short-term and long-term strength at 600°C is simulated and parameters are used successfully as equivalent alloy chemical composition, calculated by a system of unpolarized ionic radii equations. A new deformable weldable alloy based on Ni–Fe–Co is developed with working temperature up to 650°C, with $ \upsigma_u^{20 } $ = 1400 MPa, $ \upsigma_u^{600 } $ = 1200 MPa, and $ \upsigma_{100}^{600 } $ = 950 MPa, with low linear thermal expansion coefficient (α = 11.8 · 10 –6 K –1 in the temperature range 20–600°C). The alloy is structurally stable, efficient in forming and welding, and with respect to set of properties it is better than standard alloys of similar designation. New alloy structure, phase composition, and properties are described. [ABSTRACT FROM AUTHOR]

The quality and durability of metallic materials is of considerable importance in many branches of industry, in particular, in metallurgy, engineering, and construction. This article gives the results of studying the effect of strengthening solid particles on structural heterogeneity, hardness, chemical composition and wear resistance of billets, prepared by centrifugal casting. [ABSTRACT FROM AUTHOR]