Microstructure and mechanical propertiesof spray-deposited Al-Si-Fe-Cu-Mg alloy containing Mn

Al-20Si-5Fe-3Cu-1Mg alloy was synthesized by the spray atomization and deposition technique. The microstructure and mechanical properties of the spray deposited hypereutectic Al-Si alloy were studied using optical microscopy, scanning electron microscopy, X-ray diffraction, TEM (Transmission Electron Microscope) and HREM (High-resolution Electron Microscope), DSC (Differential Scanning Calorimetry), microhardness measurement, and tensile tests. The effects of Mn on the microstructural evolution of the high-silicon aluminum alloy after extrusion and heat treatment have been examined. The results show that two kinds of phases, i. e. S (Al2CuMg) and σ(Al5Cu6,Mg2), precipitated from matrix and improved the tensile strength of the alloy efficiently at both the ambient and elevated temperatures (300℃). The tensile test results indicate that the spray-deposited Al-20Si-5Fe-3Cu-1Mg alloy has better strength than the powder metallurgy processed Al-20Si-3Cu-1Mg alloy at elevated temperature.     

Synthesis and spark plasma sintering of Al-Mg-Zr alloys

Although casting is commonly used to process aluminum alloys, powder metallurgy remains a promising technique to develop aluminum based materials for structural and functional applications. The possibility to synthesize Al-Mg-Zr alloys through mechanical alloying and spark plasma sintering techniques was explored. Al-10Mg-5Zr and Al-5Mg-1Zr alloyed powders were synthesized through wet ball milling the appropriate amount of elemental powders. The dried milled powders were spark plasma sintered through passing constant pulsed electric current with fixed pulse duration at a pressure of 35 MPa. The samples were vacuum sintered at 450, 500, 550, 600 and 620℃ for 10, 15 and 20 min. The Al-10Mg-5Zr alloy displays poor densification at lower sintering temperatures of 450, 500, 550 and 600℃. Its sinterability is improved at a temperature of 620℃ whereas sintering temperatures higher than 620℃ leads to partial melting of the alloy. It is possible to sinter the Al-5Mg-1Zr alloy at 450, 500 and 550℃. The increase of sintering temperature improves its densification and increases its hardness. The Al-5Mg-1Zr alloy displays better densification and hardness compared to Al-10Mg-5Zr alloys.     

High temperature oxidation behavior of high speed steel for hot rolls material

The oxidation characteristics of high speed steel (HSS) were studied at 500 to 800℃. The non-isothermal oxidation and isothermal oxidation (500, 575, 650, 725, 800℃) of HSS were investigated by thermo-gravimetric analysis (TGA). The microstructure, morphology and oxide scale thickness of the isothermal oxidation samples were analyzed by optical microscope (OM), electron probe micro analyzer (EPMA), X-ray diffraction spectrum (XRD) and scanning electron microscope (SEM). The results indicate that the oxidation rate of HSS is very slow at 500 to 650℃, increasing gradually at 650 to 750℃, and drastically at 750 to 800℃, because the phase transformation happens at about 750℃.     

A free-cutting and ductile CuAlMnZnTiB shape memory alloy

The mechanical properties and cutting performance of the designed Cu Al Mn Zn Ti B shape memory alloy were studied by tensile test and microstructure observation. Using X-ray diffractometry, differential scanning calorimetry(DSC) and semi-quantitative shape memory effect test, the microstructure and shape memory effect were analyzed. It is found that lots of βphase and few α phase are formed in the quenching of Cu-7.5Al-9.7Mn-3.4Zn-0.3Ti-0.14B(mass fraction, %) alloy, a great deal of martensite and few α phase are formed in the aging alloy, while the annealing alloy is composed of a great deal of α phase and few βphase. The tensile strength and elongation of the annealed alloy are 649 MPa and 17.1%, respectively. Some tiny and dispersion distributed second phase particles are generated in Ti and B precipitates, greatly improving the alloy machinability.     

Origin of the pre-peak in the structure factor of liquid Fe-4.30C-0.21Ce alloy

The liquid structure of Fe-4.30C and Fe-4.30C-0.21Ce alloys was studied by high temperature X-ray diffractometer. The results show that for Fe-C alloy the nearest neighbor distance of the eutectic alloy is 0.259-0.260 nm at the temperature range of 1200-1400℃, which increases to 0.269-0.271 nm with the addition of 0.21% (mass fraction) Ce in the Fe-C alloy at the same temperature range. There is a pre-peak at Q = 15.5 nm-1 on the original intensity curve and structure factor S(Q) of the liquid Fe-4.30C-0.21Ce alloy, which was caused by the Ce atoms in the C-Ce clusters. Combined with the shared face, the tetragonal structure can meet the requirement for the distance of Ce-Ce atoms. It also shows that the cluster size in the liquid Fe-4.30C-0.21Ce alloy increases with the decreasing temperature.     

Microscopic characterization of semi-solid aluminium alloys

The microstructural evolution and element distribution of the Al-4Cu-Mg alloy during semi-solid compression were investigated,and the precipitate behavior and dislocation morphology were discussed.The experimental results show that the microstructure,the number of CuAl2(θ phase) precipitates,and the dislocation density of the Al-4Cu-Mg alloy depend apparently on the process parameters.More segregation of Cu at the grain boundary happens with an increase of deformation temperature and a decrease of strain ra...     

Microstructure and Properties of Fe-12Cr-2.5W-xSi-0.4Ti-0.3Y2O3 Alloys

Fe-12Cr-2.5W-x Si-0.4Ti-0.3Y₂O₃ alloys were fabricated by mechanical alloying and vacuum sintering. The effect of sintering temperature and Si content on the microstructure and properties of the alloy was investigated systematically. The experimental results show that the relative density and tensile strength of the alloy were increased with the elevating of sintering temperature and Si content within a certain range.The alloy with 1wt% Si sintered at 1 350 ℃ exhibited supe...     

Microstructure of the Hypoeutectic Al-Mg Alloy Solidified at 4 GPa High Pressure

High pressure solidification rules of Al-Mg alloy needs to be discussed further for its wide range of application. Mierostructures and phases of Al 25wt% Mg alloy solidified at 4 GPa were studied by optical microscope, X-ray diffractmeter, energy dispersive X-ray speetroscopy and transmission electron microscnpy （TEM）. The mierostructure evolution mechanism of Al-25Mg alloy under high pressure was analyzed. The result shows that the alloy consists of α-Al phase and AI3Mg2 phase under normal pressure. However, only Al12 Mg17 phase forms without AI3Mg2 phase at 4 GPa. In addition, Mg concentration in α-Al phase increases and that of the lattice constant also increases. The α-Al dendrite presents the broken arms under normal pressure, after high pressure solidification, the morphology of the dendrite tends to integrate and the size of the dendrite arms decreases.     

Comparative Study on Oxidation Behavior of Fe-5wt% Cr Alloy in Various Mixed Atmospheres at 900-1 000 ℃

The high-temperature oxidation behavior of Fe-5 wt% Cr alloys was investigated in both N_2+5 vol% H_2 O and N2+21 vol% O_2+5 vol% H_2 O atmospheres at 900-1000 ℃ for 120 min by the thermogravimetric analysis(TGA). The oxidation kinetics, phase composition and cross-sectional microstructure of the oxide scale were contrastively analyzed in both environments. Also, the phase composition of oxide scale was measured by X-ray diffraction(XRD). The cross-sectional microstructure and the interface elements distribution were studied by electron probe microanalysis(EPMA). The experimental results demonstrated that the growth rate and the mass gain of the oxide scale in the N_2+5 vol% H_2 O atmosphere were both significantly lower than the growth rate and the mass gain in the N_2+21 vol% O_2+5 vol% H_2 O atmosphere. The apparent layer structure of the oxide scale could be observed in an oxygen-enriched environment and did not appear in a pure water vapor without oxygen. In addition, the inner oxide layer growth mechanisms and the outward diffusion of the metal cations were introduced in the atmosphere of N_2+5 vol% H_2 O. Consequently, the effects of temperature and humid atmosphere on the Fe-Cr spinal scale evolution were also discussed.     

Fabrication and characterization of anodic oxide films on a Ti-10V-2Fe-3Al titanium alloy

Anodic oxide films of the titanium alloy Ti-10V-2Fe-3Al in ammonium tartrate electrolyte without hydrofluoric acid or fluoride were fabricated. The morphology,components,and microstructure of the films were characterized by scanning electron mi-croscopy(SEM) ,X-ray photoelectron spectroscopy(XPS) ,X-ray diffraction(XRD) ,and Raman spectroscopy. The results showed that the films were thick,uniform,and nontransparent. Such films exhibited sedimentary morphology,with a thickness of about 3 μm,and the pore diam...     

Effect of one-step aging on microstructure and properties of a novel Al-Zn-Mg-Cu-Zr alloy

The effect of one-step aging temper on the mechanical properties, electrical conductivity and the microstructure of a novel Al-7.5Zn-1.6Mg-1.4Cu-0.12Zr alloy has been investigated. The results indicated that with elevating the aging temperature from 100℃ to 160℃, the aging response rate was greatly accelerated, and the UTS at peak aging condition decreased, while the corresponding TYS increased. However, the electrical conductivity of the alloy became higher. After aging for 24 h at 120℃, the peak UTS and TYS values were achieved as 591 MPa and 541 MPa, respectively; but the alloy achieved a lower conductivity, 20.4 MS/m. When T6 temper was performed at 140℃ for 14 h, the UTS decreased only by 1% of the former, whereas the TYS and the electrical conductivity increased obviously, which were up to 559 MPa and 22.6 MS/m, respectively. The major strengthening precipitates of the peak-aged alloy were GP zones and η′ phase. The precipitates in both the matrix and the grain boundary became coarser with rising aging temperature. There were obvious PFZs along the grain boundary both in T6 conditions aged at 140℃ and 160℃.     

High-temperature Compressive Performance of Mg Alloy Foams Coated with Ni-P Layer

Mg/Ni hybrid foams were fabricated by the electroless method.The Ni-P (Nickel-Phosphorous) coatings were deposited on the surface of closed-cell Mg alloy foams.The composition,microstructure and phases of the Ni-P coatings were characterized by scanning electron microscopy (SEM),energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD),respectively.The compressive tests were performed on the Mg/Ni hybrid foams at 400 ℃ using the Mg alloy foams as a reference.The experimental results show that the yield strength,plateau stress and energy absorption capacity of the closed-cell Mg alloy foams at high temperature were improved by the Ni-P coating.And there are four main modes for the Mg/Ni hybrid foam failure at 400 ℃,i e,shearing in cell wall,bending in cell edge,shedding and cracking in Ni-P coating.     

Effect of homogenization treatment on microstructure and properties of Al-Mg-Mn-Sc-Zr alloy

The effect of homogenization on the hardness,tensile properties,electrical conductivity and microstructure of as-cast Al-6Mg-0.4Mn-0.25Sc-0.12Zr alloy was studied.The results show that during homogenization as-cast studied alloy has obviously hardening effect that is similar to aging hardening behavior in traditional Al alloys.The precipitates are mainly Al3(Sc,Zr)and Al6Mn.When homogenization temperature increases the hardness peak value is declined and the time corresponding to hardness peak value is shortened.The electrical conductivity of the alloy monotonously increases with increasing homogenization temperature and time.The decomposition of the supersaturated solid solution containing Sc and Zr which is formed during direct chilling casting and the precipitation of Al3(Sc,Zr)cause hardness increasing.The depletion of the matrix solid solubility decreases the ability of electron scattering in the alloy,resulting in the electrical conductivity increased.Tensile property result at hot rolling state shows that the optimal homogenization treatment processing is holding at 300-350 ℃ for 6-8 h.     

Effect of homogenization treatment on microstrucmre and properties of Al-Mg-Mn-Sc-Zr alloy

The effect of homogenization on the hardness, tensile properties, electrical conductivity and microstructure of as-cast Al-6Mg-0.4Mn-0.25Sc-0.12Zr alloy was studied. The results show that during homogenization as-cast studied alloy has obviously hardening effect that is similar to aging hardening behavior in traditional Al alloys. The precipitates are mainly Al3（Sc,Zr） and Al6Mn When homogenization temperature increases the hardness peak value is declined and the time corresponding to hardness peak value is shortened. The electrical conductivity of the alloy monotonously increases with increasing homogenization temperature and time. The decomposition of the supersaturated solid solution containing Sc and Zr which is formed during direct chilling casting and the precipitation of Al3（Sc, Zr） cause hardness increasing. The depletion of the matrix solid solubility decreases the ability of electron scattering in the alloy, resulting in the electrical conductivity increased. Tensile property result at hot rolling state shows that the optimal homogenization treatment processing is holding at 300-350℃ for 6-8 h.     

Ignition-proof mechanism of ZM5 magnesium alloy added with rare earth

The ignition-proof mechanism of ZM5 magnesium alloy added with 0.1% (mass fraction) rare earth (RE) was investigated. The oxide scales and substrates were characterized by scanning electronic microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and tensile test. And an oxidation model of ZM5 alloy with RE was established. The results show that the ignition temperature of ZM5 alloy is particularly elevated from 654 to 823 ℃, the microstructure is refined, and the tensile strength i...     

Fracture Behavior and Processing Deformation of C71500 Cupronickel Alloy during Hot Tensile Deformation

The hot tensile deformation properties and microstructure evolution of high purity C71500 cupronickel alloy at 1 023-1 273 K and 0.000 1-0.1 s~(-1) strain rates were studied by uniaxial hot tensile deformation method.Based on the experimental data,the flow behavior,microstructure and fracture characteristics of the alloy were analyzed after considering the influence of different deformation parameters.The relationship between microstructure and high temperature (T≥1 023 K) plasticity is discussed,and the fracture mechanism is revealed.The relationship between strain rate sensitivity coefficient and stress index and plastic deformation is discussed.The constitutive equation of the alloy is established by Johnson-Cook model.Based on the dynamic material model,the energy dissipation model is established,and Prasad’s instability criterion based on Ziegler’s expected rheological theory is used to predict the unstable region in the processing map.Processing map in hot tensile is analyzed to provide theoretical basis for different processing technology.     

Mechanical and Microstructural Characteristics of Superplastic Al-4.42Mg Aluminum Alloy

Abstract： The superplastic response of commercial 5083 alloy （Al-4. 42Mg） under uniaxial tension at strain rates ranging from 5 × 10-5 to 10-2s -1 in the temperature interval 400 -550℃ was systematically studied in this paper. The tension test was conducted on samples of rolling direction. The maximum elongation-to-failure of 486% was found at 500 % and strain rate of 10-4s-1. To identify the main characteristics of superplastic deformation and to determine the mechanism of superplastic deformation of the alloy, the microstructure and fracture of the alloy were analyzed as a function of strain, strain rate and temperature using optical microscopy （OM） and scanning electron microscopy （SEM）, the apparent strain rate sensitivity exponent ma and the apparent activation energy Qa were also studied. Based on the fracture analysis and the calculated data of m and Qa, it is suggested that the dominant deformation mechanism in the present alloy is grain boundary sliding （GBS） during the best deformation condition.     

STUDY ON MAXIMUM HYDROGEN CAPACITY FOR Zr-Ni AMORPHOUS ALLOY

To design the amorphous hydrogen storage alloy efficiently, the maximum hydrogen capacities for Zr-Ni amorphous alloy were calculated. Based on the Rhomb Unit Structure Model (RUSM) for amorphous alloy and the experimental result that hydrogen atoms exist in 3Zr1Ni and 4Zr tetrahedron interstices in Zr-Ni amorphous alloy, the numbers of 3Zr-1Ni and 4Zr tetrahedron interstices in a RUSM were calculated which correspond to the hydrogen capacity. The two extremum Zr distribution states were calculated, such as highly heterogeneous Zr distribution and homogeneous Zr distribution. The calculated curves of hydrogen capacity with different Zr contents at two states indicate that the hydrogen capacity increases with increasing Zr content and reaches its raximum when Zr is 75%. The theoretical maximum hydrogen capacity for Zr-Ni amorphous alloy is 2.0 (H/M). Meanwhile, the hydrogen capacity of heterogeneous Zr distribution alloy is higher than that of homogenous one at the same Zr content. The exrperimental resu     

Effect of Sc and Er additions on superplastic ductilities in Al-Mg-Mn-Zr alloy

The superplasticity of Al-6Mg-0.4Mn-0.25Sc-0.12Zr and Al-6Mg-0.4Mn-0.25Er-0.12Zr(mass fraction,%)alloys sheet was investigated,and the effect of Sc and Er was discussed.The results show that the superplastic ductilities of Al-Mg-Mn-Sc-Zr alloy was higher than that of Al-Mg-Mn-Er-Zr alloy at a wide temperature range of 400-540°C and high strain rate range of1.67×10-4-1.67×10-1 s-1.A maximum elongation 673%is obtained at 520°C and 1.67×10-3 s-1 in the Sc-containing alloy;while the Er-containing alloy only gets a maximum elongation 253%at 520°C and 1.67×10-3 s-1.Moreover,the average stress exponent of Sc-containing alloy is about 2.84,which is smaller than that of Er-containing alloy(3.64).Besides,the activation energies of the Sc-containing and Er-containing alloy are 84.8 k J/mol and 87.2 k J/mol,respectively.It is indicated that grain boundary sliding is the dominant mechanism during tensile deformation.According to microstructure examination,the better superplasticity of Sc-containing alloy may be attributed to the presence of Al3_(Sc,Zr)dispersoids,which can inhibit recrystallization and grain growth effectively.     

Surface analysis of chemical stripping titanium alloy oxide films

The chemical stripping method of titanium alloy oxide films was studied. An environment friendly solution hydrogen peroxide and sodium hydroxide without hydrofluoric acid or fluoride were used to strip the oxide films. The morphologies of the surface and cross-section of the oxide films before and after the films stripping were characterized by using scanning electron microscopy (SEM). The microstructure and chemical compositions of the oxide films before and after the films stripping were investigated by using Raman spectroscopy (Raman) and X-ray photoelectron spectroscopy (XPS). It was shown that the thickness of the oxide film was in the range of 5-6 μm. The oxide films were stripped for 2 to 8 min in the solution. Moreover, the effect of the stripping time on the efficiency of the film stripping was investigated, and the optimum stripping time was between 6-8 min. When the stripping solution completely dissolved the whole film, the α/β microstructure of the titanium alloy Ti-10V-2Fe-3Al was partly revealed. The stripping mechanism was discussed in terms of the dissolution of film delamination. The hydrogen peroxide had a significant effect on the dissolution of the titanium alloy anodic oxide film. The feasibility of the dissolution reaction also was evaluated.