Band 36, Heft 1 -

In order to investigate the hot deformation behaviors of as-extruded 7075 aluminum alloy, the isothermal compressive tests were conducted at the temperatures of 573, 623, 673 and 723 K and the strain rates of 0.01, 0.1, 1 and 10 s −1 on a Gleeble 1500 thermo-mechanical simulator. The flow behaviors showing complex characteristics are sensitive to strain, strain rate and temperature. The effects of strain, temperature and strain rate on flow stress were analyzed and dynamic recrystallization (DRX)-type softening characteristics of the flow behaviors with single peak were identified. An artificial neural network (ANN) with back-propagation (BP) algorithm was developed to deal with the complex deformation behavior characteristics based on the experimental data. The performance of ANN model has been evaluated in terms of correlation coefficient ( R ) and average absolute relative error (AARE). A comparative study on Arrhenius-type constitutive equation and ANN model for as-extruded 7075 aluminum alloy was conducted. Finally, the ANN model was successfully applied to the development of processing map and implanted into finite element simulation. The results have sufficiently articulated that the well-trained ANN model with BP algorithm has excellent capability to deal with the complex flow behaviors of as-extruded 7075 aluminum alloy and has great application potentiality in hot deformation processes.

The MnO–SiO 2 slag in equilibrium with Mn–Si melts with a Si molar ratio between 0.1 and 0.3 at 1,700 K was a single liquid phase. However, it was liquid phase saturated with solid MnO or solid SiO 2 in the case of X Si less than 0.1 or greater than 0.3, respectively. Based on a subregular solution model, the calculated saturated solubility of oxygen in Mn–Si melts was 0.0236 mass % in pure manganese at 1,700 K and increased with the increasing silicon in the range of X Si from 0.1 to 0.3. However, the saturated solubility of oxygen decreases as the silicon exceeded 0.3, and the minimum solubility was 0.0041 mass % in pure silicon at 1,700 K. The results could be used to predict the compositions of endogenous oxide inclusions and evaluate the cleanliness of manganese ferroalloy.

Al 2 O 3 /YAG/ZrO 2 eutectic in situ composite has now been considered as the new generation of high-temperature structural material due to its excellent performance even close to its melting point. In this work, hypereutectic Al 2 O 3 /YAG/ZrO 2 in situ composite is manufactured by the horizontal laser zone melting technique. The relationship between the solidification microstructure and the solidification parameters is studied. The minimum lamellar spacing is as finer as 0.20 μm when the laser scanning rate is 800 μm/s. Compared with eutectic Al 2 O 3 /YAG/ZrO 2 , hypereutectic exhibits more regular and finer microstructure at the similar conditions. Meanwhile, it is found that the lamellar spacing remains almost as constant at a certain high solidification velocity. The maximum hardness and fracture toughness are 15.9 GPa and 4.2 MPa · m 1/2 , respectively.

The response of true stress to strain rate, temperature and strain is a complex three-dimensional (3D) issue, and the accurate description of such constitutive relationships significantly contributes to the optimum process design. To obtain the true stress–strain data of ultra-high-strength steel, BR1500HS, a series of isothermal hot tensile tests were conducted in a wide temperature range of 973–1,123 K and a strain rate range of 0.01–10 s −1 on a Gleeble 3800 testing machine. Then the constitutive relationships were modeled by an optimally constructed and well-trained backpropagation artificial neural network (BP-ANN). The evaluation of BP-ANN model revealed that it has admirable performance in characterizing and predicting the flow behaviors of BR1500HS. A comparison on improved Arrhenius-type constitutive equation and BP-ANN model shows that the latter has higher accuracy. Consequently, the developed BP-ANN model was used to predict abundant stress–strain data beyond the limited experimental conditions. Then a 3D continuous interaction space for temperature, strain rate, strain and stress was constructed based on these predicted data. The developed 3D continuous interaction space for hot working parameters contributes to fully revealing the intrinsic relationships of BR1500HS steel.

The present paper investigated the impact of cerium on the corrosion resistance of zinc coating in a 5 % NaCl solution. Electrochemistry was used to measure the electrochemical parameters to compare the corrosion resistance of the zinc coating with that of the cerium conversion coating on the galvanized layer. SEM/EDS and XRD were adopted to analyze the appearance and phases of corrosion products of the cerium conversion coating and to probe the impact of cerium on the corrosion behavior of zinc coating in the Cl – media. The results showed that the cerium conversion coating formed on the zinc coating increased the zinc’s corrosion resistance effectively, conversion coating with lower cerium content protected the substrate poorly, resulting in easy erosion of the zinc coating in the Cl – media. The corrosion products mainly consist of complexes, such as Zn(OH) x Cl y and Ce(OH) x Cl y .

The superplastic tensile behaviors of Ti-6Al-4V (TC4) titanium alloy were tested at temperature ranges from 850 ℃ to 950 ℃ and tensile velocities in the range of 0.3–6.0 mm/min. The microstructures of the specimen under various deformation parameters were evaluated by scanning electron microscope (SEM) and transmission electron micrograph (TEM). The results indicate that the maximum tensile force decreases with the increase of temperature and the decrease of tensile velocity. The optimum tensile elongation of 1120.5 % is attained at 900 ℃ and 0.6 mm/min. α and β phase grain sizes increase with the increase of temperature and the decrease of tensile velocity. β phase volume fraction plays an important role in superplasticity, and the best elongation is attained under the condition of ~7.0 µm α phase and ~4.0 µm β phase and β phase volume fraction is about 31 %. High deformation velocity leads to finer grains and results in larger tensile force.

Titanium and its alloys are widely used in many fields, including aerospace and the chemical and biomedical industries. This is due to their mechanical properties, excellent corrosion resistance, and biocompatibility although they do have poor wear resistance. In this study, a duplex layer was successfully formed on the commercially pure titanium surface by duplex treatments (plasma nitriding and physical vapor deposition (PVD)). In the initial treatment, plasma nitriding was performed on the pure titanium samples and in the second treatment, the nitrided samples were coated with CrN by PVD. The friction and wear properties of the duplex-treated samples were investigated for tribological applications. Surface morphology and microstructure of the duplex-treated samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). In addition, the tribological properties were investigated using pin-on-disc tribometer. A compound layer composed of ε-Ti 2 N and δ-TiN phases and a diffusion layer formed under the compound layer were obtained on the surface of pure titanium after the nitriding treatments. CrN coated on the nitrided surface provided an increase in the surface hardness and in the wear resistance.

Particulate reinforcement composite ZrB 2p /6061Al was fabricated from Al-K 2 ZrF 6 -KBF 4 by a direct melt reaction. Laser surface melting was used to improve the surface strength of the in situ ZrB 2p /6061Al composite, which includes a series of laser-melted composites with different laser power and cooling conditions processed by a 2-kW yttrium aluminum garnet laser generator. The surface substructure of these laser-treated specimens was investigated by light optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffractometry and transmission electron microscopy. The penetration depth of the molten pool increases with increases in power density, and decreases with increases in the degree of undercooling. The Vickers hardness of the laser-melted composites reached 60–75.2 HV in liquid nitrogen and 56–64.0 HV in air, and increased by 50.4 % and 28 %. Grain refinement with decreased cellular spacing is important in strength performance. Because of a thermocapillary flow vortex and α-Al phase precipitation, nano-ZrB 2 particles were distributed along the cellular dendrite boundary as observed by scanning electron microscopy. This was considered to be a key factor responsible for the improved mechanical composite properties. When cooling under liquid nitrogen, the thermal mismatch stress between particles and the matrix generates a high dislocation density. The dislocation grows along the interface between the matrix and particles and provides the laser-melted composites with additional strength.

High iron bauxite ore is a typical unmanageable polyparagenetic resource and owns high comprehensive utilization value. Separation of iron from fine particles of high iron bauxite ore by the process of metallized reduction and magnetic dressing was researched systemically. The effect of magnetic field intensity, reduction temperature, reduction time, mole ratio of fixed carbon to reducible oxygen (FC/O) and ore particles size on separation indexes was researched. The results show that, with the conditions of reduction temperature of 1,400 °C, reduction time of 180 min, FC/O of 2.0, ore particle size of –2.0 mm and magnetic field intensity of 40 KA/m, about 89.24 % of the iron could be removed from high iron bauxite ore as metallic iron. Meanwhile, 86.09 % of the aluminum is stayed in non-magnetic fraction as alumina. However, the formation of hercynite (FeAl 2 O 4 ) limits the reduction rate of iron oxides to metallic iron. The lower reduction conditions and higher recovery ratio of iron could be achieved with adopting ore-coal composite agglomerates or adding catalyst.

The creep failure for a lattice truss sandwich panel structure has been predicted by finite element method (FEM). The creep damage is calculated by three kinds of stresses: as-brazed residual stress, operating thermal stress and mechanical load. The creep damage at tensile and compressive loads have been calculated and compared. The creep rate calculated by FEM, Gibson–Ashby and Hodge–Dunand models have been compared. The results show that the creep failure is located at the fillet at both tensile and creep loads. The damage rate at the fillet at tensile load is 50 times as much as that at compressive load. The lattice truss panel structure has a better creep resistance to compressive load than tensile load, because the creep and stress triaxiality at the fillet has been decreased at compressive load. The maximum creep strain at the fillet and the equivalent creep strain of the panel structure increase with the increase of applied load. Compared with Gibson–Ashby model and Hodge–Dunand models, the modified Gibson–Ashby model has a good prediction result compared with FEM. However, a more accurate model considering the size effect of the structure still needs to be developed.

This paper reports, for the first time, an analysis of the effect of high-current pulsed electron beam (HCPEB) on a hypoeutectic Al–10Si alloy. The Al–10Si alloy was treated by HCPEB in order to see the potential of this fairly recent technique in modifying its wear resistance. For the beam energy density of 3 J/cm 2 used in the present work, the melting mode was operative and led to the formation of a “wavy” surface and the absence of mass primary Si phase and eutectic microstructure. The surface nanocrystallization of primary and eutectic Si phases led to the increase in macro-hardness of the top surface layer, and the wear resistance was drastically improved with a factor of 4.

In this paper, the effects of temperature and atmosphere on the gasification reaction of ferro-coke were investigated in consideration of the actual blast furnace conditions. Besides, the microstructure of the cokes was observed by scanning electron microscope (SEM). It is found that the weight loss of ferro-coke during the gasification reaction is significantly enhanced in the case of increasing either the reaction temperature or the CO 2 concentration. Furthermore, compared with the normal type of metallurgical coke, ferro-coke exhibits a higher weight loss when they are gasified at the same temperature or under the same atmosphere. As to the microstructure, inside the reacted ferro-coke are a large amount of pores. Contrary to the normal coke, the proportions of the large-size pores and the through holes are greatly increased after gasification, giving rise to thinner pore walls and hence a degradation in coke strength after reaction (CSR).