Papers by Author: Liang Zuo

Abstract: The deformation behavior of DC cast Al-2Si and Al-15Si alloys have been studied by means of compression test at temperature range of 300-500°C and strain rate range of 0.01-5 s-1. The results show that the flow stress of the Al-Si alloys increases with decreasing compression temperature and increasing strain rate. The flow curves determined from the compression tests exhibit that the deformation of the materials is controlled by two competing mechanisms: strain hardening and flow softening. Higher silicon content in the alloys also leads to higher flow stress during deformation and tend to show more significant flow softening. Particle damage during the deformation may have an influence on the flow curves of the alloys.

Abstract: The 4.2wt.%Si non-oriented electrical steel thin sheets with the thickness of 0.30mm were produced by the conventional procedure including hot rolling, cold rolling and annealing. The recrystallization texture was analyzed with emphasis on the effect of normalizing annealing. The results show that the  fiber with peak at {111} is weaker and η fiber is stronger in the sheets with normalizing annealing than those without normalizing annealing, either under the cold rolled reduction of 77% or 86%. Effects of normalizing annealing on the recrystallization texture can be explained in terms of the characteristic of the shear bands formed during cold rolling process.

Abstract: A nanostructured surface layer was produced on an 20CrMo steel plate by means of ultrasonic shot peening (USSP) treatment. Plasma nitriding of the treated and un-treated sample were investigated by using structure analysis (X-ray diffraction, optical microscopy, and transmission electron microscopy ) as well as hardness measurements. It was found that a nanostructured surface layer sample developed a compound layer twice as thick as that in a coarse-grained sample under the same plasma nitriding conditions (530 oC for 6 h). In addition, the USSP nitrided sample exhibited higher hardness and thicker hardened surface layer in comparison with coarse-grained nitrided sample.

Abstract: The deformability and the microstructures of Al-12.2Si-0.6Mg alloy during hot-rolling were investigated by means of rolling the specimens of wedge bars with length of 180mm and width of 30mm, which had front thickness of 5mm and back thickness of 44mm.The wedge bars were cut from the ingots of the Al-12.2Si-0.6Mg alloy by the semi-continuously direct chill (DC in short) casting. The specimens of wedge bars were hot-rolled following holding between 410°Cand 480°C for different time. The results show that the size, morphology, distribution characters of eutectic Si particles in the Al-12.2Si-0.6Mg alloy can be remarkably modified by semi-continuously DC casting, which consists of coarse ribbon-like Si-particles with less than 5μm in length and 1μm in width and quite a lot eutectic phases of less than 0.4μm in size and space. The results also show that the ingots of the Al-12.2Si-0.6Mg alloy by the semi-continuously DC casting can possess excellent deformability during hot-rolling if the extent of heating is provided over 440°C for 60min and 410°C for 120min, and they cannot emerge cracked edges with the compression ratio of 85% by single-pass rolling. Their hot-plasticity depends on the size and space between eutectic phases in the ingots. Hot-rolling deformation makes ribbon-like Si phases in them crack and spheroidize, and then results in the sizes of coarse Si particles tending to be consistent.

Abstract: The effect of cold deformation on the yield strength and precipitate behavior of Al-1.3Mg-1.2Si-0.5Cu-0.7Mn alloy sheet subjected to T4P temper for automotive body panels before and after paint-bake treatment were investigated by tensile test and differential scanning calorimetry (DSC) analysis. The results show that the T4P alloy sheet has significant work-hardening response (WHR), and the yield strength increment exceeds 190MPa as the tensile deformation strain approaches 15%. The unstrained T4P alloy sheet has obvious paint-baking response (PBR), and the yield strength increment is up to 80MPa, while the PBR of the cold stretched T4P alloy sheets decrease with increasing level of tensile deformation, and the minimal PBR is only 17.8MPa. The prior tensile deformation accelerates the precipitation of β″ and β′ phase from the T4P alloy matrix during paint-bake cycle but weakens the age-hardening response (AHR) and PBR of T4P alloy sheet. Moreover, it is evident that the T4P alloy sheet simulation paint-bake treated at 170°C for 30min can not fully exert the aging potential of the alloy sheet.

Abstract: The effects of the magnetic field intensity on microstructure and crystallographic orientation of proeutectoid ferrite in Fe-0.36C alloy have been investigated. Results show that the amount of the Widmänstatten ferrite decreases with the increase of the magnetic field intensity. The transformed proeutectoid ferrite tends to elongate and align along the field direction due to the magnetic dipolar interaction. This tendency is more pronounced when the field intensity increases. Moreover, the enhancement of the <001> fiber component along the traverse field direction by magnetic field is obvious when the field intensity is stronger.

Abstract: In the present work, we summarized two calculation methods to determine some specific crystallographic elements based on electron diffraction orientation measurements by SEM/EBSD or TEM. The first one is to determine the twin type and twinning elements of crystal twins based on the minimum shear criterion, using the experimentally determined twinning plane for Type I twin and compound twin or twinning direction for Type II twin as initial input. The method is valid for any crystal structure. The second one is one to determine the plane indices of the faceted interfaces where the orientation relationships (ORs) between the adjacent crystals are reproducible. The method requires one prepared sample surface instead of two perpendicular surfaces. These methods are expected to facilitate the related microstructural characterizations.

Abstract: Specimens cut from a cold-rolled IF steel sheet of 1 mm thickness were respectively annealed at 750°C for 20min under a range of DC electric fields (1kV/cm~4kV/cm). The Effect of electric field strength on recrystallization texture of IF steel sheet was studied by mean of X-ray diffraction ODF analysis. It was found that γ-fiber textures were notably enhanced as electric field strength increased. The strength of γ-fiber textures got their peak values as the applied electric field reached to 4kV/cm. The possible reason for such phenomena was discussed in the viewpoint of interaction between the applied electric field and the orientation-dependent stored-energy in deformed metals which is known as the driving force for recrystallization during annealing.

Abstract: Effects of magnetic field intensity on carbon diffusion in pure iron in the single-phase austenite region were investigated. Specimens of high purity iron (99.99%) were buried in an air-proof melting pot filled up with cementation agent, and respectively subjected to isothermal annealing at 930° for 25 min with a heating rate of 5°C /min, and then cooled in the furnace. A magnetic field with different intensity was applied during the whole heating, isothermal holding and cooling processes. The results showed that the magnetic field annealing obviously hinders the carbon diffusion in the direction perpendicular to the magnetic field direction and this effect increased with the enhancement of magnetic filed intensity.

Abstract: The effect of Co addition on the properties of Ni_8-xMn₄Ga₄Co_x (x=0, 0.5, 1, 1.5 and 2) ferromagnetic shape memory alloys are systematically investigated by means of the first–principles calculations within the framework of density functional theory (DFT) using the Vienna ab initio software package (VASP). The formation energy results indicate that the added Co preferentially occupies the Ni sites in Ni₂MnGa alloy. With the increase of the Co content, the optimized lattice parameters of the parent phase decreases regularly, whereas the lattice parameter a of the martensite increases and c decreases, thus leading to a decrease of the c/a ratio. The effects of Co addition on phase stability of the paramagnetic and ferromagnetic austenite are displayed. The difference in the magnetic properties in the investigated series can be explained from the electronic density of states analysis. The aim of this paper is to provide theoretical guidance for the development of new promising ferromagnetic shape memory alloys with optimized properties.