Modeling of recrystallization behaviour of AA6xxx aluminum alloy during extrusion process

An innovative approach was introduced for the development of a AA6063 recrystallization model.This method incorporated a regression-based technique for the determination of material constants and introduced novel equations for assessing the grain size evolution.Calibration and validation of this methodology involved a combination of experimentally acquired microstructural data from the extrusion of three different AA6063 profiles and results from the simulation using the Qform Extrusion UK finite element code.The outcomes proved the agreement between experimental findings and numerical prediction of the microstructural evolution.The trend of the grain size variation based on different process parameters was accurately simulated,both after dynamic and static recrystallization,with an error of less than 25% in almost the whole sampling computations.

60Si2Mn和5160H弹簧钢的脱碳行为

用显微组织法比较了６０Ｓｉ２Ｍｎ和５１６０Ｈ弹簧钢在不同加热条件下的脱碳行为．结果表明,两种弹簧钢的脱碳深度随提高加热温度和增加加热时间增大．Ｓｉ增加奥氏体中碳的活度使６０Ｓｉ２Ｍｎ钢表面脱碳较５１６０Ｈ严重．

钢铁件渗碳层深度的电磁无损检测

1．问题提出 某厂生产的拖拉机油泵齿轮所用材料为18CrMnTi，要求其渗碳层深度为1．1～1．5mm．所用设备为RJJ-90型滴入式气体渗碳炉，具体渗碳工艺如图1所示。为严格控制渗碳层深度，我们通过长期实践提出了如下控制措施。

几种常用的脱碳层深度测定方法

介绍了几种常用的脱碳层深度测定方法(包括显微组织法、硬度法、碳含量测定法等)的测试原理、适用范围及注意事项,并对各方法的优缺点进行了比较。结果表明:每种测试方法均有其局限性,具体测试方法的选择必须基于被测对象的属性及客户要求而定,众多方法中金相法和显微硬度法的应用最为广泛。

Microstructures and mechanical properties of 2024Al/Gr/SiC hybrid composites fabricated by vacuum hot pressing

The 2024Al/Gr/SiC hybrid composite plates with 5%-10% SiC particles （volume fraction） and 3%-6% flaky graphite （Gr） （volume fraction） were fabricated by vacuum hot pressing and hot extrusion processing. The effects of SiC and Gr on the microstructures and mechanical properties of the composites aged at 160, 175 and 190℃ were studied by optical microscopy, scanning electron microscopy （SEM）, and hardness and tensile tests. The results indicate that the SiC particles have a more obvious effect on accelerating the aging response as compared with the Gr. Both the tensile strength and elongation are reduced by the Gr and SiC particles added into the matrix, while the Gr has a more negative influence on the elongation than the SiC particles. The tensile strength （ab）, yield stress （as） and elongation （δ） of the 2024Al/3Gr/10SiC composite aged at 165℃ for 8 h are 387 MPa, 280.3 MPa and 5.7%, respectively. The hybrid composites are characterized by ductile fracture, which is associated with the ductile fracture of the matrix and the tearing of the interface between the matrix and the particles.

Expression of COX-2, PCNA, Ki-67 and p53 in gastrointestinal stromal tumors and its relationship with histopathological parameters

AIM: To investigate the expression of Cyclooxygenase-2 (COX-2), proliferating cell nuclear antigen (PCNA), Ki-67 and p53 in gastrointestinal stromal tumors (GISTs) and its relationship with histopathological parameters. METHODS: Twenty-five GISTs were examined by light microscopy and immunohistochemistry. c-kit, CD34, SMA, S-100 protein, COX-2, PCNA, Ki-67 and p53 were detected immunohistochemically and the relationship was evaluated among histopathologic parameters such as mitotic index (MI), tumor grade, tumor size, COX-2, PCNA, Ki-67 and p53. RESULTS: COX-2 protein expression was found in 19 of 25 (76%) of the tumors, and expression was noted in the cytoplasm of the tumor cells. p53 was significantly related to MI and tumor grade but no relationship was found between COX-2, proliferation markers and MI, tumor grade and tumor size. CONCLUSION: COX-2 is expressed in most GISTs and it may play an important role in the proliferation and progression of these tumors or a useful marker to identify GIST. Although immunohistochemical assessment of p53 can be used for distinguishing the risk groups of GISTs, tumor size and mitotic rate should be considered at the same time.

Shape controlling and property optimization of TA32 titanium alloy thin-walled part prepared by hot forming

The hot flow behaviors,microstructure evolution and fractographs were studied to optimize the hot forming process of the TA32 titanium alloy thin-walled part.A set of microstructure-based constitutive equations were developed based on the experimental data,which described the relationships among the hot flow stresses and the evolution of phase volume fraction,dislocation density,grain size and damage.The constitutive model was imported into ABAQUS 6.14 to simulate the hot forming process for a typical thin-walled part.The effective strain,dislocation density and damage distribution as well as forming defects of formed parts under different process parameters were predicted.A qualified part without wrinkling and fracture defects was produced at a loading speed of 5 mm/s at 800℃ by the modified blank shape,where the maximum damage value was only 18.3%.The accuracy of constitutive model and finite element(FE)simulation was verified by the microhardness tests,which indicates that the FE model based on physical internal-state variables can well optimize the hot forming process of TA32 titanium alloy complex parts.

Microstructure and photocatalytic activity of Ni-doped ZnS nanorods prepared by hydrothermal method

Pure ZnS and Ni^2+-doped ZnS nanorods (Zn1-xNixS, x=0, 0.01, 0.03, 0.05 and 0.07, mole fraction,%) were synthesized by hydrothermal method. The effects of Ni2+ doping on the phase-structure, morphology, elemental composition and optical properties of the samples were investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray energy dispersive spectrometry (EDS) and ultraviolet–visible spectroscopy (UV-Vis), respectively. The photocatalytic activity of Zn1-xNixS nanorods was evaluated by the photodegradation of organic dyes Rhodamine B (RhB) in aqueous solution under UV light irradiation. The results show that all samples exhibit wurtzite structure with good crystallization. The morphologies are one-dimensional nanorods with good dispersion, and the distortion of the lattice constant occurs. The band gap of Zn1-xNixS samples is smaller than that of pure ZnS, thus red shift occurs. Ni^2+-doped ZnS nanocrystals can enhance photocatalytic activities for the photodegradation of RhB. Especially, Zn0.97Ni0.03S sample exhibits better photocatalytic performance and photocatalytic stability for the decomposition of RhB.

Parametric optimization of friction stir welding parameters of marine grade aluminium alloy using response surface methodology

Friction stir welding between AA5052-H32aluminium plates is performed by central composite design technique of response surface methodology.It is found that the welding parameters such as tool pin profile,tool rotational speed,welding speed,and tool tilt angle play a major role in deciding the joint characteristics.The joints fabricated using tapered square pin profile tool with a tool rotational speed of600r/min,welding speed of65mm/min,and tool tilt angle of1.5°result in an unexpected weld efficiency of93.51%.Mathematical models are developed to map the correlation between the parameters and responses(ultimate tensile strength and elongation)and these models are optimized to maximize the ultimate tensile strength of the friction stir welded joint.Response plots generated from the mathematical models are used to interpret the interaction effects of the welding parameters on the response variables.Adequacy of the developed models is validated using analysis of variance(ANOVA)technique.Results from the confirmatory experiments plotted in scatter diagram show a good agreement with predicted models.Different grain structures in various zones of the weld are examined by observing the micro and macro structures of the weld.

Preparation and properties of Ni-coated WC powder and highly impact resistant and corrosion resistant WC-Ni cemented carbides

WC powders were uniformly coated by Ni nanoparticles through a combined chemical co-precipitation and subsequent high temperature hydrogen reduction strategy(abbreviated as CM-WCN),and then were consolidated by vacuum sintering at 1450°C for 1 h to obtain WC−Ni cemented carbides.The microstructure and properties of the as-consolidated CM-WCN were investigated.The average grain size of WC in the consolidated CM-WCN was calculated to be in the range of 3.0−3.8μm and only few pores were observed.A relative density of 99.6%,hardness of HRA 86.5 and bending strength of 1860 MPa were obtained for the CM-WCN−10wt.%Ni,and the highest impact toughness of 6.17 J/cm^(2 )was obtained for the CM-WCN−12wt.%Ni,surpassing those of the hand mixed WC−Ni(HM-WCN)cemented carbides examined in this study and the other similar materials in the literature.CM-WCN cemented carbides possess excellent mechanical properties,due to their highly uniform structure and low porosity that could be ascribed to the intergranular-dominated fracture mode accompanied by a large number of plastic deformation tears of the bonding phase.In addition,the corrosion resistance of CM-WCN was superior to that of HM-WCN at the Ni content of 6−12 wt.%.

Prediction of grain scale plasticity of NiTi shape memory alloy based on crystal plasticity finite element method

Grain scale plasticity of NiTi shape memory alloy(SMA)during uniaxial compression deformation at 400℃was investigated through two-dimensional crystal plasticity finite element simulation and corresponding analysis based on the obtained orientation data.Stress and strain distributions of the deformed NiTi SMA samples confirm that there exhibits a heterogeneous plastic deformation at grain scale.Statistically stored dislocation(SSD)density and geometrically necessary dislocation(GND)density were further used in order to illuminate the microstructure evolution during uniaxial compression.SSD is responsible for sustaining plastic deformation and it increases along with the increase of plastic strain.GND plays an important role in accommodating compatible deformation between individual grains and thus it is correlated with the misorientation between neighboring grains,namely,a high GND density corresponds to large misorientation between grains and a low GND density corresponds to small misorientation between grains.

Sol-gel auto-combustion synthesis of K_xNa_(1-x)NbO_3 nanopowders and ceramics: Dielectric and piezoelectric properties

The KxNa1-xNbO3 nanopowders with cubic-like morphology and an average size of about 50 nm were synthesized by sol-gel auto-combustion method.And then,the ceramics were prepared and the phase transition,microstructure and electrical properties of the KxNa1-xNbO3 ceramics were investigated.Pure perovskite phases of the KxNa1-xNbO3 ceramics were confirmed by XRD patterns and the K0.50Na0.50NbO3 ceramics show the coexistence of orthorhombic and monoclinic structures.SEM micrographs show that all samples have bimodal grain size distributions and the number of the small grains decrease with increasing K+content in the bimodal grain size distribution system.The K0.50Na0.50NbO3 ceramics with the uniform grain size and the maximum density show excellent electrical properties withεr=467.40,tanδ=0.020,d33=128 pC/N and kp=0.32 at the room temperature,demonstrating that the properties of the K0.50Na0.50NbO3 powers prepared by sol-gel auto-combustion are excellent and the ceramics are promising lead-free piezoelectric materials.

Effects of forging parameters on uniformity in deformation and microstructure of AZ31B straight spur gear

The effects of forging parameters on the deformation and microstructure distributions of as-forged straight spur gears wereinvestigated by finite element(FE)simulation and statistical analysis method.Spur gear forging using the movable cavity die designwas investigated by integrating the FE method with the microstructure evolution models for AZ31B magnesium alloys.The requiredinputs such as flow stress curves and microstructure evolution models,were obtained through the Gleeble thermal mechanical testingand quantitative metallography analysis method.Numerical simulation and experimental examination confirm that both thedeformation and microstructure are non-uniformly distributed in the as-forged gears.Decreasing deformation temperature orincreasing strain rate is beneficial to obtaining fine-grained microstructure but is harmful to the uniformity in deformation ormicrostructure.The level of the non-uniformity results from the complex shape of gear and the friction between the billet and dies,which is closely associated with the characteristics of flow stress curve.

Interaction between Spermatozoa and the Different Epithelia along the Female Reproductive Tract of Mustelus schmitti

The presence of sperm was observed in different organs of the reproductive tract of M. schmitti. These were the club, baffle and terminal zone of the oviducal gland, posterior portion of the uterus and in the cervix. This fact allowed for consideration not only its storage but its interaction with the female reproductive tract epithelia as well. SEM （microscopic observation studies） detected loose and sole spermatozoa in the club and baffle zones in a pregnant female. On the other hand, histochemical techniques showed sperm storage tubules of the terminal zone, which contain bundles of sperm, do not stain AB （alcian blue） or PAS （periodic acid schiff）. Disintegration of some of the male gametes was observed in the posterior part of the uterus with TEM （transmission electron microscopy） studies which would indicate a first uterine sperm selection. The uterine epithelial cells involved in this process showed an important level of secretion vacuoles suggesting an interaction with sperm cells. Sperm in the cervix was found without the matrix that constitutes the spermatozeugmata formed in the male tract. Some heads of the sperm were uncurled while they were interacting with the cervical cells.

Effect of brazing parameters on fillet size and microstructure of cladded fin-microchannel tube joints

This work concerns the optimization of furnace brazing conditions for joining micro-multiport aluminum tubes and fins made with AA4343/AA3003/AA4343 brazing sheet in mini-assemblies mimicking the core of an automotive heat exchanger.Taguchi method was used for design of experiment,considering five process parameters with two levels of values.The aim was to maximize the fillet size of the brazed joints,which has an important influence on the thermal integrity and mechanical properties.Fillet length measurements of brazed joints were performed with a metallographic microscope.The statistical analysis allowed to obtain the optimum values of process parameters(peak temperature,residence time,heating rate,microchannel tube type and flux).At a 95%confidence level,the variability of fillet length is most significantly affected by the peak brazing temperature(77%),residence time(15%)and heating rate(7%).The predicted maximum fillet length was(152±11)μm,which was corroborated by confirmation trials.The microstructural analysis of tube−fin joints showed that variations in peak temperature and residence time affect only the size of the eutectic zone of fillet formed,but not the nature or composition of the constituent phases.