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The effect of Er and Zr microadditions on changes in the structure of aluminum alloy 7075 during homogenization is studied. Additions of Er and Zr cause grain refinement and reduce the size of coarse nonequilibrium grain-boundary eutectic. Eutectic dissolves completely during the homogenization process; long rods are transformed into spherical particles. Homogenization regime substantially affects secondary Al3(Er, Zr) phase precipitation. Two-stage homogenization (400°C, 12 h + 465°C, 12 h) leads to fine and uniformly distributed particles of Al3 (Er, Zr) with an average radius of 28.9 nm and volume fraction of 1.3 ×10–3.

The static recrystallization behavior of 7075 aluminum alloy containing Al3(Sc,Zr) phase prepared by casting and the relationship between recrystallization behavior and mechanical properties were studied. The addition of Sc and Zr made the Sc–Zr–7075 aluminum alloy remain the most of fibrous structure and high-density dislocations formed in the extrusion process, resulting in the recrystallization fraction of the alloy decreasing from 35% to 22%, and the corresponding fraction of substructure increasing from 59% to 67%. The Sc and Zr effectively inhibited the recrystallization behavior of 7075 aluminum alloy mainly, which was attributed to the fact that the existence of fine and coherent Al3(Sc,Zr) phase (r = 35 nm, f = 1.8×10−3) strongly pined the dislocations and grain boundaries, preventing the dislocations from rearranging into sub-grain boundaries and from developing into high angle grain boundaries, and further hindering the formation and growth of recrystallized core of the alloy.

A 7075 aluminum alloy is widely used in the fields of transportation and aerospace because of its high strength and low density. In this paper, the effect of homogenization annealing on the microstructure of 7075 aluminum alloy was studied. The microstructure and second phase evolution of 7075 aluminum alloy were analyzed by optical microscope (OM), X-ray diffractometer (XRD), scanning electron microscope (SEM), energy spectrometer (EDS) and differential scanning calorimeter (DSC). The results showed that the as-cast microstructure of 7075 aluminum alloy was equiaxial crystal, and non-equilibrium eutectic microstructure Mg(Zn, Cu, Al)2 produced along the grain boundary. In the subsequent first-order homogenization annealing, part of Mg(Zn,Cu,Al)2 was converted to Al2CuMg phase. However, the transformation was not fully complete. Mg(Zn,Cu,Al)2 was then completely converted to Al2CuMg phase in the second order homogenization annealing.

Magnesium alloys have been widely applied in many fields, because of their high strength-to-weight ratio. However, magnesium alloys have high chemical activity and are easily corroded. The poor corrosion resistance of magnesium alloys greatly limits its further application. In this paper, the zinc phosphate conversion coatings were prepared on the surface of AZ91D magnesium alloys. Nano-zinc oxide was the source of zinc and the zinc phosphate conversion coatings were prepared by the given process: 1.25 g/L NaNO3, 3 g/L C6H8O7 H2O, 2.5 g/L NaF, 5.5 g/L ZnO, 12.5 mL/L H3PO4, reaction temperature 50°C, reaction for 30 minutes. The full immersion uniform corrosion test was conducted for the fabricated coatings. The morphology and composition of corrosion in different corrosion stages were characterized by XRD, SEM and other microscopies. The results showed that: (1) the corrosion process of the conversion coatings could be divided into three stages: the dissolution of the conversion coatings, the corrosion of the matrix and the deposition of insoluble matter; (2) XRD analysis and other methods found that the pine-needle magnesium oxychloride compounds were formed in the process of immersion firstly, and it was dissolved into Mg(OH)2 over time; (3) With the extension of immersion time, Mg(OH)2 increased continuously and played a major role in corrosion prevention. The deposited Mg(OH)2 was divided into two layers. In the initial deposition stage, it was mainly evenly dispersed on the surface of the alloy to form a tightly arranged inner layer. Afterwards, the crystals of Mg(OH)2 agglomerated and formed a sphere, becoming the outer layers.

The influence of various retrogression and re-ageing (RRA) treatment processes on the hardness, electrical conductivity and corrosion behavior of graphene/7075 aluminum matrix composite were investigated. The results showed that the hardness decreased swiftly at the initial stage and short time to peak value as the retrogression temperature (170 °C, 180 °C, 190 °C, 200 °C) rises. In the RRA 180 °C/120 min process, the electrical conductivity and peak-aging Brinell hardness were 37.9%IACS, 192.8. This RRA treatment possessed excellent pitting corrosion resistance, and the corresponding pitting potential (Epit), the passivation potential (Epit-Ecorr), the pitting corrosion current density (Logicorr) were -0.756V, 0.558V, -1.836A/cm2, respectively. This enhance can attribute that the continuous η phase distributed along the grain boundary became intermittent and coarse in the retrogression stage.

In this work, the preparation of graphene by chemical oxidation reduction method and a series of chemical reactions to get graphene oxide, with the preparation of graphene composites by simply chemical reduction method for the preparation of palladium/graphene composites. Through the chemical reduction method, the small size of Pd nanoparticles is acquired by controlling the content of reducing agent. The Pd nanoparticles on graphene surface is 10nm size and evenly distributed. Pd2+ adsorption on graphene surface and in situ were partially reduced to Pd to Pd2+ nanoparticles by the reducibility of graphene. In the process, the graphene was reduced to graphene and the final compound was thinner and more transparent than the pre-experiment oxide. The oxygen-containing functional groups on the surface of the graphene have influence to the nucleation and growth of metal nanoparticles and KI can control the morphology and size of nanoparticles. The particle size and dispersion uniformity have great influence on the catalytic performance of composites, the smaller particles have better catalytic performance. Keywords:palladium, graphene composites, nanoparticles

The effects of rare earth Y addition on microstructure and properties of pure copper were investigated. Mechanical test, electrical test, oxidation resistance test, metalloscope, scanning electronic microscope (SEM) and X-ray difffraction (XRD) were performed to study the properties, microstructure and constitution. The results showed that both the hardness and antioxidant properties obviously increased with the increase of Y, confirmed the successful refinement role of Y. A small amount of Y (less than 0.5 wt.%) could improve the electrical conductivity of pure copper. When the Y content reached 0.2 wt.%, pure coppers obtained optimum electrical conductivity which is 96.8% IACS. However, over-added Y (>0.5 wt.%) resulted in second phase of Cu7Y coarsening and non-homogeneous microstructures forming, which reduces the conductivity of copper. In addition, Y can effectively purify the organization of molten copper.

The effect of aging treatment on the aging hardening of 0% Yb and 0.4% Yb modified A356.2 alloy was investigated by hardness measurements and optical microscope. In this work, A356.2 was first subjected to 535°C for 5h and then subjected to 150°C, 180°C for 2h-12h hours. Results show that during aging process, there was a hardness peak along the increasing of aging temperature and time. With increasing aging progress, the morphology of Si phases became shorter and spherical. After optimum time, Si phases was coarse and the dendritic grain was broken. The peak-aged of unmodified alloys was 150°C for 10h and 180°C for 6h，and corresponding hardness values were 62.35HB and 77.10HB, respectively. With Yb addition, the hardness reached 87.58HB and 98.28HB on peak aging of 150°C/8h and 180°C/ 6h, respectively. The greatest degree of hardness was increased by 40.46% and 27.47%, combined with no Yb addition. XRD shows the interplanar crystal spacing of A356.2 with 0.4% Yb addition, which was larger than fresh A356.2 alloy. When adding 0.4%Yb under 180°C for 6h aging progress, the ultimate tensile strength was 284 MPa 12.7% increasing compared with former work.

Copper matrix composites (CMCs) are widely used in electrical equipment and electrical contact materials due to their excellent electrical properties. Al2O3 powders are widely used as a reinforcing agent to enhance mechanical properties of MMCs. The xAl2O3/Cu (x =0, 0.2, 0.5, 0.7, and 1.0wt. %) composites were prepared via vacuum arc melting method. The mechanical and electrical properties were obtained by measuring the hardness and conductivity. The morphology of copper and Al2O3/Cu composites was characterized by optical microscopy (OM) and scanning electron microscopy (SEM). With the addition of Al2O3 from 0.2 wt. % to 1.0 wt. %, the relative densities of composites decreased from 98.5% to 97.0%. The hardness of the composites increased with increase in the Al2O3 powders content. The hardness of 1.0Al2O3/Cu composites was 57.9 HB, which was higher than that of pure Cu by 18.6%.. With the addition of Al2O3, the IACS% of Al2O3/Cu composites decreased from 88.97 to 86.16.

7085 aluminum alloy has been widely used in aviation and aerospace because of high fracture toughness, high strength, slow quench sensitivity and low density. In the as-cast microstructure, it is not avoidable for massive un-dissolved secondary phases and dendritic segregation. The microstructure of as-cast high strength 7085 aluminum alloy after two-stage homogenization was studied by optical microscopy (OM), X-ray diffractometer (XRD), scanning election microscopy (SEM), energy dispersive spectrometer (EDS) and differential scanning calorimeter (DSC). It was found that the severe dendritic segregation exists in as-cast 7085 aluminum alloy and a small amount of Al7Cu2Fe exists in the as-cast 7085 alloy. The evolution of primary eutectic structure of 7085 alloy consists of three processes: the dissolution of non-equilibrium eutectic phase α (Al) + Mg (Zn)2, the transformation from Mg (Zn)2 to Al2CuMg and the dissolution of new phase Mg (Zn)2. A suitable two-stage homogenization scheme for as-cast 7085 aluminum alloy is 300°C/8 h + 465°C/24 h.

A356.2 aluminum alloy (Al–7Si–0.35Mg) has been widely used in automotive and aircraft industries. Previous studies found that the metamorphism effect of rare earth is better than other type of elements because of long modification time and good stability. The influence of Yb addition (0%, 0.2%, 0.4% and 0.6%) and T6 heat treatment on A356.2 alloy has been investigated in this work. The microstructures and mechanical properties of the specimen after T6 treatment were examined by optical microscope, scanning electronic microscope and tensile tests. Experimental results showed that Yb could reduce the size of α-Al and change the Si morphology from needle-like to fine spheroidal particles. With the increase of Yb content, the ultimate tensile strength increased gradually. When adding 0.4%Yb, the alloy achieved the highest ultimate tensile strength (252 MPa) and hardness (97.3HB), 10.12% and 37.66% higher than the alloy with no Yb addition. Tensile fracture analysis showed that the fracture mechanism for A356.2 aluminum alloy after T6 treatment is transgranular/intergranular mixed mode of fracture.

SiC/Gr/Al composites with the graphite particle size of 1, 6 and 20 μm were fabricated by squeeze casting technology and the effects of graphite particles on machinability were investigated. Results show that with increasing size of graphite particles, the tool wear has very little change, but the cutting force decrease noticeably. Compared to SiC/Al composite, the cutting forces increase steadily with increasing the cutting speed during machining SiC/Gr/Al composite, the tool life is prolonged 42 and 59%, respectively, at speed of 20 and 30 m min− 1 when machining SiC/Gr(6 μm)/Al composite. It is a result of the solid lubrication of graphite particle preventing for growth of adhesive wear.

The influence of homogenisation annealing process on microstrucure of 7085 Al alloy has been investigated by optical microscopy(OM), scanning electron microscopy combined with energy dispersive X-ray spectroscopy (EDX), X-ray diffraction(XRD), and differential scanning calorimetry (DSC). The results show a large amount of skeletal Mg(Zn, Al, Cu)2 phase and AlZnMgCu phase distributed as eutectic microstructure on crystal boundaries, and some impurity phase of triangle or square Al18Mg3Cr2 in the interior of grain in as-cast 7085Al alloys. In combination with DSC and OM observation, the temperature of homogenisation annealing is determined lower than 473°C. With increasing temperature of homogenising annealing, the woven crystal microstructure on the grain boundary and part lager block second phase in interior of grain decreases, and grain boundary turns to be discontinuous. 7085Al alloys are treated by homogenising annealing of 470°C/24 h, grain boundary turns to be discontinuous, uniform and fine ...

Metal matrix composites reinforced by graphene particles exhibit physical and mechanical property and are developed and qualified for use in aerospace structure, bioengineering, energy storage material and photoelectric device. In the present paper, graphene was fabricated by modify Hummers method, and then was surface modified by chemical plating copper. The graphene/Al composites were fabricated by powder metallurgic method. Morphology characterization of graphene and composites were detected by XRD and SEM,the fabrication parameters of composites were optimized by testing harness and density. The volume fraction of graphene particles was 3%, the density of composites was maximum of 96.5%. The hardness had a maximum of HB 42.6, and the hardness of graphene/Al composites increased by 33.5%.

TiO2 thin films with outstanding photocatalysis can potentially be used for photocatalysis device in the field of environmental protection. TiO2 thin film (99.99%) was fabricated successfully by power metallurgy. The effect of sputtering power on TiO2 thin films by radio frequency magnetron sputtering was investigated. The results show that the higher sputtering power is beneficial for the growth of Rutile structure with superior photocatalysis. With the increasing of sputtering power, the rate of methyl orange degradation increases under UV light irradiation. The degradation rate of TiO2 thin film under sputtering power 75W and 165W is 40% and 80% respectively. This is attributed to the increase of the rutile phase with many defects and dislocation network under higher sputtering power.

Cu3N thin films can potentially be used for development of optical storage devices and integrate circuit of semiconductor. In this study the Cu3N films were deposited on glass substrate successfully by reactive direct current magnetron sputtering at different N2/(N2+Ar) flow ratio. The results showed that the nitrogen partial pressure affected the preferring orientation of the thin films when the sputtering power and substrate temperature was fixed. With increasing N2/(N2+Ar) flow ratio from 10% to 90%, Cu3N(111) orientation with rich-copper changed to Cu3N(100) orientation with rich nitrogen, the transmittance of the thin films improved gradually, and the corresponding optical band gap (Eg) increased from 1.10 eV to 1.21eV. The resistivity of copper nitrogen films changed from 5.62Ω.cm to 3.00×103Ω.cm at the scope of 10%~90% of N2/(N2+Ar) flow ratio.

The Cu3N films were deposited successfully by reactive direct current magnetron sputtering, the films were comprehensively and systematically characterized by X-ray diffraction analyzer (XRD), UV-Visible spectrophotometer, four-probe resistance tester and other instruments. Results showed that under low deposition power (80W~100W), crystal orientation increased, which is attributed to higher energy under higher power. When sputtering power exceeded the value, excessive energy led to anti-sputtering hindering the process of further nucleation and growth of films. The transmittance of the films deposited under 100W reached the peak value of 78% on the scope of near-infrared light, and optical band gap (Eg) of 1.35ev. The resistivity of Cu3N films increased from 9.68×102Ω.cm to 2.12×103Ω.cm with increasing in sputtering power up to 100W.

The TiO2 reduced graphene oxide (TiO2/RGO) nanocomposites were synthetized by hydrothermal method. The microstructure and morphologies of them were characterized by XRD and SEM. The photocatalytic activity was investigated by the methyl orange photogradation under UV illumination. The results showed that GO sheets had wrinkles and folds, and anatase-structured TiO2 covered on graphene surface after hydrothermal reaction. Compared to the TiO2 nanoparticles, the TiO2/RGO nanocomposites display the higher photogradation efficiency. In 90 minutes, the gradation percentage of TiO2/RGO nanocomposites to methyl orange is 80%, higher than TiO2 nanoparticle (40%). This is attributed to the large surface area of TiO2/RGO nanocomposites and their improved separation efficiency of electron-hole pair.

ZnO doped Al2O3and ZrO2(ZAZO) thin films were deposited by the radio frequency magnetron sputtering on substrate temperature with 100°C, 150°C, 200°C, 250°C and 300°C. The surface morphology and electrical properties of the films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and four-probe tester. The results showed that the substrate temperature obviously influenced the grain size of ZAZO films. The ZnO thin film had the largest crystallization orientation for the (002) peak and the smallest FWHM value at substrate temperature of 250°C. As the temperature increasing, the resistance of films gradually decreased till reaching a minimum at 250°C and then rised. Due to the increasing of Al and Zr concentrations into ZnO lattice, the Al ions created an abundance number of free electrons in the ZnO lattice, and in turn, the electrical conductivity increased. In addition, the improvement of film in the crystalline state results in the film resistivity decreases.

In this research, graphite has been found to have excellent tribological properties as a lubricant additive. To reduce high friction and wear in cylinder liner piston ring friction pairs, modified flocculent graphite have been prepared via chemical technology. The morphology and microstructure of modified flocculent graphite were investigated via SEM, EDS, XRD and IR. In this study, varying concentrations (0.1, 0.5, and 0.9 wt.%) within modified flocculent graphite were dispersed at 350 SN lubricant for Gasoline Engine. Suspension stability of the lubricating oils with modified flocculent graphite and graphite as determined by ultraviolet-visible light (UV-VIS) spectrophotometry. The friction and wear characteristics of lubricants containing materials of modified flocculent graphite were evaluated under reciprocating test conditions to simulate contact. The morphology and microstructure of the friction pair tribofilms produced during frictional contact were investigated via SEM, EDS and a 3D surface profiler. The results show that scratching, pits, furrows and adhesive wear took place, respectively, on the worn surfaces of friction pairs. But, modified flocculent graphite showed excellent friction reducing and anti-wear performance and subsequently has great potential for the application of anti-wear.

Aluminum Borate Whisker/Aluminum Phosphates composites (ABW/AP) added Si3N4were prepared with pressure sintering technique. The influence of Si3N4on the mechanical properties and dielectric properties were investigated. After sintered at 1050°C for 1h, the results showed that the flexural strength of the composites with 5wt% Si3N4addition reach 167.29MPa,the dielectric constant (ε) and loss tangent (tanδ) of the composites are 2.99 and 0.0089 at 10GHz. The testing results was discussed.

The copper based electric contact materials with multicomponent substance were obtained by powder metallurgy. The hardness and density of the samples increase with adding proper amount of Y 2 O 3 . Adding 1.5 wt.% Y 2 O 3 the hardness of the sample reaches the maxim and the density of sample reaches the maximum by adding 2 wt.% Y 2 O 3 . In this paper, the effects of addition of Y 2 O 3 on the performance of copper based contact materials were studied by metallographic microscope, XRD, SEM in details. Moreover, the mechanism of the effects was discussed.