镁合金消失模铸造模样热解产物及其阻燃性分析

本文对镁合金消失模铸造过程中模样材料的热解特性进行了测试和分析，得出了聚苯乙烯（EPS）、聚甲基丙烯酸甲酯（EPMMA）、共聚物（StMMA）三种常用模样材料在镁合金浇注过程中的热解产物组成主要是苯乙烯、少量的液态产物和一定量的气态产物；通过对镁合金实际浇注过程中模样材料热解过程观察和分析，认为小分子主要有还原性的气态物质组成，具有很好的阻燃性。     

可控气压下镁合金消失模铸造工艺参数的研究

研究了模样密度、涂层厚度、浇注温度、真空度等工艺参数对可控气压下镁合金消失模铸造时液态金属的充填形态和充型速度的影响,以及充型速度与充型形态之间的关系.结果表明:在可控气压下镁合金消失模铸造过程中,液态镁合金呈拱形平稳向前推进,并随着泡沫模样密度的降低、涂层厚度的减小、浇注温度和真空度的提高,充型速度提高.各因素对充型速度的影响效果由大到小的顺序是:泡沫模样密度→涂层厚度→浇注温度→真空度.通过分析实验数据,建立了可控气压下镁合金消失模铸造的充型速度的非线性数学模型.     

镁合金消失模铸造模样的热解特征

采用气相色谱分析的方法对三种泡沫模样:聚苯乙烯(EPS)、共聚物(StMMA)、聚甲基丙烯酸甲酯(EPM-MA)的热解特性进行了分析,同时对镁合金消失模实际浇注的热解气体进行了测试,得出了镁合金消失模不周泡沫模样热解产物的种类和分布.研究指出,StMMA的品质及其热解特性表明它更适合于镁合金消失模铸造,有利于高性能复杂薄壁镁合金消失模铸件的成形.     

铝合金消失模铸造壳体针孔度控制

1 铝合金消失模铸造铝液充型特点及对铝液要求 铝合金消失模铸件是由铝液将白模"消失"掉,铝液取代白模空间,将白模空间变成铝液空间,冷凝形成铝合金铸件.在此过程中,铝液流动前沿存在着复杂的反应:①铝液前沿液态和少量气态白模热解产物与铝液、涂料及干砂间进行着物理化学反应和质量传输;②铝液与涂层和干砂及液(气)化及未液(气)化白模进行着热的传导、对流、辐射;③铝液热解白模、升温涂层、干砂等使得铝液温度下降.     

镁合金真空低压消失模铸造的技术特征与实践

详细介绍了镁合金在真空低压消失模铸造下的技术特征.试验研究表明真空低压消失模铸造的流动性受充型气体的流量与压力、浇注温度、涂层厚度、泡沫密度、真空度等多方面的因素影响;在低充型速度和低真空度的条件下,液态镁合金在真空低压消失模铸造过程中的充型形貌均呈现以内浇道为中心的拱形层状推进流动,如充型速度加快,金属液流动前沿拱形形貌更加突出,而真空度增加会出现明显的"附壁效应";与重力消失模铸造比较,真空低压消失模铸造镁合金铸件凝固更呈现"同时凝固"特征;由于快速充型、压力下凝固,镁合金真空低压消失模铸造零件的铸态抗拉强度(σb=180.8MPa)、屈服强度(σ0.2=113.2 MPa)、伸长率(δ=4.4%),高于重力消失模铸造、树脂砂真空型铸造的铸态性能,达到了金属型铸造的铸态性能,经热处理达到了压力铸造镁合金的性能范围.浇注实践表明,真空低压消失模铸造对液态镁合金,具有良好的抗氧化保护能力、优良的浇注充型性能和力学性能,可铸造出高精度的、薄壁复杂的镁合金消失模铸件.     

镁合金真空低压消失模铸造影响因素及充型能力的研究

介绍了一种新的真空低压消失模铸造工艺,分析了该工艺的工作原理和影响因素,并采用窗体及电机壳体模样测试了AZ91D镁合金在该工艺条件下的充型能力。研究表明：充型气体的气压与流量、泡沫模样的密度与裂解特性、涂层厚度及透气性、浇注温度、真空度等是镁合金真空低压消失模铸造过程中的主要影响因素。窗体和电机壳体成功浇注试验证明了真空低压消失模铸造新工艺大大提高了镁合金的充型能力,消除了重力下消失模铸造镁合金充型能力差、易形成浇不足和冷隔缺陷的缺点。     

真空度对镁合金低压真空消失模铸件质量的影响

以获得高内在质量的镁合金消失模铸件为目标,试验研究了镁合金低压真空消失模铸造工艺中真空度对铸件质量的影响.试验结果表明:负压真空度过低不利于模样热解产物的排除,过高会引起液态金属前沿产生"附壁效应",充型时真空度大小可以根据铸件的复杂程度和壁厚来选择,壁厚较大铸件可以用较低的真空度,壁厚较薄的铸件应使用较高真空度.镁合金真空低压消失模铸造最佳的真空度参数范围为0.02～0.03 MPa.     

镁合金负压消失模铸造充型过程的研究

镁合金负压消失模铸造充型过程的直接观察实验的结果表明 ,不抽真空时 ,金属前沿呈微凸形平缓地向前推进 ;抽真空时 ,因在模样分解产物的排除方向上存在一正的压力梯度 ,金属液优先沿模样壁充填型腔使流动形态呈不规则的凹形形态。提高真空度 ,不规则的流动形态的凹度更大且充型时间明显缩短。浇注方式对流动形态和充型时间的影响不大 ,与顶注和侧注相比 ,底注时充型过程最为平稳 ,且其充型时间最长。根据试验结果 ,建立了镁合金负压消失模铸造充型过程的模型     

消失模铸件常见缺陷及控制

结合大量生产实例及试验数据,分析了消失模铸造生产中变形、塌箱、粘砂、冷隔、夹砂及碳夹杂等常见缺陷产生的原因并给出了防止措施.研究结果表明,消失模铸件质量受泡沫模样及其热解特性、涂料、造型特点、高温铁液、负压度、浇注过程及充型凝固过程等因素综合影响.     

消失模铸造传质过程与铸件品质控制

消失模铸造是1 种有利于环保的近净成形铸造方法，在消失模工艺的浇注过程中，模样分解为液态或气态产物。为了生产合格的铸件，须选用具有合适透气性和液态产物浸润能力的涂料，以控制分解产物的传质过程。说明设计在高温下测试涂料透气性的仪器是必要的。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。