Applied Mechanics and Materials Vols. 477-478

Abstract: The true stress-strain curves of AZ91 magnesium alloy as-homogenized were studied with compression tests on Gleeble 3500 thermal simulated test machine at 200°C—400°C and strain rate range of 10^-3S^-1 — 5S^-1. Critical recrystallization behavior of AZ91 magnesium alloy was investigated by using strain hardening rate. The relationship between critical stress of dynamic revrystallization and temperatures and strain rates is determined by the curves between strain hardening rate and flow stress. According to the irreversible principles of thermo dynamics, the critical stresses at different temperatures and strain rates are calculated by two derivative of θ—σ curves. The map of the critical stress-temperatures-strain rates is established.

Abstract: Converter Slag is a by-product during steelmaking. Reusing the slag as Portland cement material can be regarded as a way to reduce environmental pollution. However, the poor grindability caused by complex chemical composition of the slag makes it very difficult to be used in cement industry. To better understand its grindability, the mineral characteristic of converter slag was investigated in this paper. Experimetal slags of CaO-MgO-SiO₂-Fe₂O₃, CaO-MgO-SiO₂-Fe₂O₃-P₂O₅ and CaO-MgO-SiO₂- Fe₂O₃-P₂O₅-Al₂O₃ were synthetized according to physical and chemical properties of actual converter slag. The mineral structures of these slags were analyzed by SEM and EDS. The results show that actual and synthetic slags have mainly three mineral, where dicalcium silicate with little phosphorus presented dark gray, periclase presented black and the matrix phase of dicalcium ferrite. Moreover, phosphorus largely dissolves in the 2CaO∙SiO₂ in the form of 3CaO∙PO₄, and the other minerals don’t contain phosphorus. A Little aluminum has a little influence on the mineral formation of the slag.

Abstract: Al-12Si-3.2Cu-1Mg-2.4Ni-χTi (χ=0, 0.2) alloys were prepared by squeeze casting process, and then heat-treated. The mechanical properties were tested at 350°C, the microstructure and phases in them were investigated by optical microscope, SEM, EDS and XRD. It is found that the grain size has an obvious increment after 0.2 wt. % Ti additions to Al-12Si-3.2Cu-1Mg-2.4Ni, and the ultimate tensile strength at elevated-temperature increased accordingly. Intermetallic compounds, such as γ-Al₇Cu₄Ni, M-Mg₂Si, Q-Al₅Cu₂Mg₈Si₆ and δ-Al₃CuNi existing in alloys with and without Ti addition. Needle-like Ti containing phase with the elements of Al, Si and Ti created in Al-12Si-3.2Cu-1Mg-2.4Ni-0.2Ti alloy, and the eutectic Si is found to distribute by the side of Ti containing phase.

Abstract: The fatigue characteristic of 2124 aluminum alloy in T851 condition was investigated by means of scanning electron microscopy (SEM) and transmission electron microscope (TEM). And the result shows that, the fatigue life is closely related to the thickness of plates, this is because that different thickness of plates results in the variation of grain size, grain boundaries and substructures of alloy, which thus influence the fatigue behavior of 2124-T851 alloy. The number of grain boundaries along the propagation direction of cracks and the amount of substructures after heat treatment increase with the decline of thicknesses of 2124 alloy plates, while the grain size is reverse. However, no obvious size and dispersion changes for the precipitates. Comparatively, the fatigue resistance performance of 30mm thickness plate is better than the 40mm and 55mm thickness plates, which is due to the more profitable grain size, grain boundary and substructure.

Abstract: The high strength and low cost Ti-Fe based alloy was produced by double vacuum induction melting method followed by hot deformation. The microstructure has been investigated by Optical Microscopy, Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The microstructure of as-forged alloy is composed of α and β phase without the precipitation of TiFe intermetallic compound. The Ti-Fe-Al alloys show good comprehensive mechanical properties, demonstrating ultimate tensile strength of 1100MPa and elongation above10%. The results indicate the Fe is a good candidate for solution strengthening and simultaneously increasing ductility in titanium alloys. Effect of the Fe and Al elements on the microstructure and mechanical properties have been discussed.

Abstract: The texture feature and grain refinement effect of Al-5Ti-C alloy on pure aluminum were analyzed and its attenuation mechanism was discussed by using X-ray diffraction (XRD), scanning electron microscopy (SEM), optical microscopy (OM) and other experimental methods.The results show that: Al-5Ti-C alloy is composed of Al, TiAl₃ and TiC. Al-5Ti-C alloy has a good grain refining capacity for commercially pure aluminum. During the heat preservation process, due to precipitation of titanium compound in the aluminum melt, refinement effect of Al-Ti-C alloy is declined.

Abstract: The dynamic mechanical property and microstructure evolution of commercial pure titanium with initial lamellar dislocation boundary structures were studied at different strain rate compression. The experiments were conducted to the cylindrical specimens using Gleeble-3500 thermal mechanical simulation machine at room temperature. With increasing of the strain rate, strain rate strengthening effect was found in the material. New dislocation boundary structures along impact direction were generated which perpendicular to initial dislocation boundary. Then the S bands boundary structure was formed by interaction between new and initial dislocations. It can be supposed that initial dislocation boundary are sheared and kinked by new dislocation slipping.

Abstract: Using the first-principles calculations within the density functional theory (DFT), we have investigated the structure, magnetism and half-metallic stability of Co₂FeGa Heusler compound under pressure from 0 to 50GPa. The results revel that the lattice constant is gradually shrank and total magnetic moment in per unit slightly decreased with increasing pressure, respectively. Moreover, with the increase of the pressure, the Fermi level will move towards high-energy orientation. When the pressure reaches at 30GPa the most stable half-metallicity is observed which the Fermi level is located at the middle of the spin-minority gap.

Abstract: The microstructures and mechanical properties of the Cu-17Ni-3Al-X alloy hot-extruded at different extrusion ratios were investigated by tensile and hardness testing, optical microscope (OM) and scanning electronic microscope.The results show that the dynamic re-crystallization occurs when the extrusion ratio λ increases from 8 to 25. The grain size and the second phases of the extruded alloys are obviously finer than that of the as-cast alloy. The mechanical properties of the extruded alloys are improved remarkably. The alloy with the λ of 25 obtained the tensile strength of 1025MPa, Brinell Hardness of 312HB and elongation of 10.0% which is 35%, 14% and 355%, respectively, higher than that of the as-cast alloy.

Abstract: The texture feature and grain refinement effect of Al-5Ti-B alloy on pure aluminum were analyzed and by adjusting the cooling velocity and casting temperature of molten aluminum,the influence of Al-5Ti-B alloy on solidification microstructure of pure aluminum was studied by using X-ray diffraction (XRD), scanning electron microscopy (SEM), optical microscopy (OM) and other experimental methods. The results show that: Al-5Ti-B alloy is composed of Al, TiAl₃ and TiB₂. under the same solidified velocity,with the increase of the mass fraction of Al-5Ti-B alloy among the aluminum melt, solidification structure of pure aluminum equiaxed dendrite size small. But at the same additives of Al-5Ti-B alloy, the cooling rate and casting temperature have significant effects on the number and size of equiaxial crystal. Faster cooling rate and lower casting temperature of molten aluminum are favorable for the formation of thin equiaxial crystal of solidification microstructure.