Advanced Materials Research Vols. 476-478

Abstract: The influence of Y on the microstructure and damping capacity of AZ91D based alloys was investigated by optical microscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and dynamic mechanical analysis. The results show that, with increasing Y content, the grain size of α-Mg matrix decreases tremendously and the distribution of β-Mg17Al12 phase is transformed from discontinuous network to fine particles. Meanwhile, a needle-shaped Al4MgY phase mainly distributing at the grain boundaries is identified. The damping capacity of the studied alloys shows sustained enhancement with increasing temperature. As to the strain dependent damping capacity, with the increase of Y content, the damping value of AZ91D alloy decreases gradually before Y content reaches to 0.5wt.%, and fluctuates when Y addition is between 0.5wt.%~0.9wt.%. G-L dislocation model was employed to explain the effects of parameters on damping capacity of magnesium alloy.

Abstract: Duplex ageing treatment was performed on AZ80 magnesium alloy deformed at room temperature. This study focus on the ageing treatment process on the deformed alloys, and the table of L16(45) of orthogonal design was adopted in the experiment. The influence of ageing treatment process on the hardness and microstructure were analyzed and discussed. The experimental results show that the hardness increased with increase of deformation ratio, which is up to the peak value at 30%. The order of effects on hardness is the time of second-stage ageing treatment, the temperature of second-stage ageing treatment, the time of first-stage ageing treatment, the temperature of first-stage ageing treatment in turn. The optimal heat treatment process were obtained, which were consisted of solution treated at 420°C for 10h, deformation with 30% ratio, first-stage aged at 140°C for 12h, followed by second-stage aged at 180°C for 16h. The sample of AZ80 magnesium alloy treated under the optimal process has homogeneous and fine grains and comprehensive property.

Abstract: The two Cu₆₀Ni₂₀Cr₂₀ alloys with the different grain size were prepared by conventional casting (CA) and mechanical alloying (MA) through hot pressing. Effect of the grain size on electrochemical corrosion behavior of the two Cu60Ni20Cr20 alloys was also studied in solutions containing chloride ions. Results show that the free corrosion potentials of the two alloys move toward to negative values, corrosion current densities increase and therefore corrosion rates become faster with the increment of chloride ion concentrations. CACu₆₀Ni₂₀Cr₂₀ alloy and MACu₆₀Ni₂₀Cr₂₀ alloy have passive phenomena in 0.05mol/L Na2SO4 neutral solution, but passive phenomena become weak or disappear when the chloride ions are added. Corrosion rates of the nanocrystalline MACu₆₀Ni₂₀Cr₂₀ alloy become slower than those of the coarse grained CACu₆₀Ni₂₀Cr₂₀ alloy in solutions containing the same chloride ion concentrations because MACu₆₀Ni₂₀Cr₂₀ alloy is able to produce large concentrations of grain boundaries and passive elements is able to diffuse quickly to form the protective film.

Abstract: The water droplets in the microemulsion system of xylene/water/Span-80 can act as a micro-reactor which solubilize Zr(NO₃)₄, Y(NO₃)₃, and dimethyloxalate. The homogeneous precipitation reactions will take place in the restricted spaces determined by the droplets size. The micro-reactors help us obtain spherical nanometer ZrO₂(Y₂O₃) reunion powders successfully. The spherical nanometer ZrO₂(Y₂O₃) reunion powders and the precursor powders were characterized by means of TG-DTA, XRD, SEM and laser particle analyzer. It was investigated that the effect of Span-80 concentration on morphology and crystal phase composition of reunion powders. The result shows that as the volume ratio V_xylene:VSpan_-80:V_water= 40:1.0:8, the well spherical and excellent dispersion reunion powders with size of 4-16um were prepared after the precursor powders were sintered at 600°C for 2h. The Span-80 concentration has no effect on the crystal phase composition of reunion powders, however, has significant effect on the morphology of reunion powders.

Abstract: AZ91 alloy powder was prepared by two-roller quenching equipment. The powders were consolidated and extruded into bar. The microstructures of the powders and bars were observed by optical microscope (OM), XRD, HRTEM and SEM. The results suggested that the grain size of the powder were equiaxed with the sizes of about 1~5μm. The as-extruded alloy bars retain equiaxed grains with a large number of precipitated phases, β-Al12Mg17 and AlMg2Zn. The alloy exhibited excellent mechanical properties, the ultimate and yield tensile strength were 383.2MPa and 275.1MPa respectively. The shape of the precipitated phase was approximately globular with the size of about 50~200nm.

Abstract: The matrix of AZ91D Magnesium alloy can be covered with a coat of protective film through anodic oxidation treatment, it’s able to make certain that the optimal surface combination properties are generated especially on corrosion resistance. This thesis is devoted to the research on forming process of anodic oxide film of AZ91D magnesium alloy; the experiment shows the formation of anodic oxide film at constant pressure is accompanied by precipitation of gases and fluctuation of current, XRD indicates that anodic oxide film is composed of MgO、γ-Al2O3 and a small amount of Si.

Abstract: In this paper, an as-extruded Mg-10Gd-2Y-0.5Zr alloy was compressed at 3265 s^-1 and -20 °C using a split Hopkinson pressure bar (SHPB) machine. Details about the initial texture and the lattice parameters of the as-extruded alloy were obtained by pole figures combined by orientation distribution function (ODF) and X-ray diffraction (XRD) Rietveld refinement method, respectively. It can be obtained that the maximum average orientation factor being 0.297 can be obtained at 45^o angled to the extruded direction that is the force axis, resulting in the fracture of the impact compressed sample along a plane orientated at an angle of ~45^o to the compression axis. Analysis of the fracture reveals that the fracture forms near the periphery of one face of the specimen and then penetrates into the bulk material subsequently meet near the other face. Even though the local shear deformation exists in the compressed sample, the fracture of the as-extruded Mg-10Gd-2Y-0.5Zr alloy compressed at 3265 s^-1 and -20 °C is not caused by forming the adiabatic shear band (ASB).

Abstract: The effect of aging condition on elevated temperature tensile strength and microstructure of an Al-Cu-Mg-Ag alloy was investigated. The tensile strength of 165°C/14h samples was greater at room temperature and 200°C, while the 165°C/2h samples got superior tensile properties at 250°C and 300°C. The microstructure contained mainly of Ω plates in both conditions, and as the increasing of exposure temperature, the coarsening of Ω precipitates occurred by the solution of small particles and the growth of large particles, resulting in an increase in the average particle size, and the decrease in the number of precipitates.

Abstract: AZ80 magnesium alloys were deformed at different temperature (270°C, 300°Cand 330°C)with different deformation ratio from 10% to 50%. The influence of varying the deformation temperature and ratio on the microstructure and hardness of AZ80 magnesium alloy was studied. The experimental results show that the hardness increased with the increasing of deformation and the hardness is up to the peak value with 40% deformation at 300°C. The microstructure was homogeneous and the grain was refined after hot deformation.The roles of both deformation strengthening and dispersition strengthening were to im prove the mechanical property of AZ80 magnesium alloy.