基于PAGM模型的浇注系统对螺旋桨铸件夹渣率的影响

基于分散相粒子运动模型,考虑夹渣在随流运动过程中动态聚合长大现象,构建了夹渣聚合长大模型(PAGM,Particles Aggregation Growth Model)。采用PAGM对铝合金螺旋桨铸件浇注过程中夹渣的运动轨迹、聚合长大行为及最终位置进行了模拟计算和试验验证。在此基础上研究了浇注系统对铸件夹渣分布及夹渣率的影响。结果表明,浇注系统设计对夹渣运动行为及分布有较大影响,PAGM可有效提升对铸件夹渣分布预测的准确性,为铸件优化设计及失效分析提供参考。     

铸造过程中渣粒运动轨迹及夹渣位置研究

铸件中的夹渣缺陷破坏了材料的连续性,易形成局部应力集中和疲劳裂纹扩展源,严重地影响了铸件的服役性能。由于渣粒数量众多,运动轨迹复杂,对其运动轨迹及停留位置预测较困难。本文通过铝合金应力框铸件的浇注试验,基于分散相粒子模型进行了充型和凝固过程中渣粒运动轨迹跟踪,分析了等直径二氧化硅渣粒在铸件和浇注系统各个关键位置的运动特征,获得了充型和凝固过程中金属液的流动规律、温度变化特点对渣粒运动轨迹及最终停留位置的影响规律。结果表明,金属液在充型过程中的局部流场特点和充型路径对夹渣缺陷的分布有较大的影响,型腔中产生涡旋流场处和流量较大的区域均易出现夹渣缺陷。同时验证了冒口具有明显的局部集渣作用,合理的开设和布置冒口能有效地降低铸件夹渣率。采用分散相粒子模型能有效地预测铸造过程中夹渣粒子的运动轨迹,为提高铸件质量提供参考。     

砂型铸造内燃机铝铸件气孔的防止方法

在砂型铸造内燃机铝铸件生产中,经常出现大量气孔缺陷,影响生产进度的完成。为解决这一问题,我们进行了认真分析,找出了产生气孔的原因并采取相应措施加以防止,取得了较满意的结果,现简单总结如下与同行交流。1　铝合金液对气体、特别是氢气的溶解特性铝合金在熔炼过程中及铝合金液在液态状态下容易吸收大量气体,特别是溶解大量氢气,而在固态状态几乎不溶解气体,或者溶解的极少。铝合金在凝固过程中,如果所溶解的气体、特别是氢气,不能及时被排出熔体,那么,凝固后就将在固体(铸件)内形成气孔(或针孔)缺陷。2　气孔产生的原因及防止办法2…     

铝合金壳体铸件翻转浇注工艺研究

翻转浇注是重力浇注的一种特殊形式,它有许多优点,有利于解决复杂铸件浇注过程产生的缩孔、缩松、气孔、夹杂等铸造缺陷.对航空用铝合金壳体铸件的浇注工艺进行了研究,分析了传统重力底注铝合金壳体铸造缺陷的原因,提出了翻转浇注工艺并进行了改进.结果表明,改进后的工艺使铝合金壳体铸件的合格率增至90％,获得了无夹渣和气孔的铸件.     

铸钢件渣气改善方法探究

渣眼、气孔、砂眼是铸钢件的常见铸造缺陷,不仅影响铸件的美观,也会影响其使用性能,甚至使铸件报废。本文通过探讨销孔座铸钢件产生渣气孔的各种原因和影响因素,通过多次改善试验,结合使用超级过滤技术,在诸多因素中抓住主要影响铸造渣孔的原因,从而解决了销孔座铸件渣气孔的缺陷问题。     

华铸CAE软件在壳型铸造激冷铸铁凸轮轴工艺优化中的应用

介绍了壳型铸造激冷铸铁富康轿车凸轮轴批量生产初期存在的主要问题.采用华铸CAE软件,通过对凸轮轴充型过程流动场的模拟,揭示了卷气(气孔)、夹渣、冲砂的部位与形成原因;通过对流动场温度场的耦合计算,揭示了铸件产生冷隔浇不足、材质等缺陷的部位与形成原因.模拟结果表明,通过工艺优化后生产的凸轮轴有效地防止了铸件气孔、夹渣冲砂、冷隔浇不足、材质等缺陷,取得了明显的效果.     

浇注系统设计对铸件夹渣行为的影响研究

采用分散相粒子模型对铝合金重力浇铸件的夹渣行为进行了模拟,通过实验对该模型的可靠性进行了验证.在此基础上设计了4种浇注系统并进行了挡渣模拟,以探索浇注系统对铸件夹渣行为的影响.结果表明:半封闭平直横浇道具有离心式集渣包的浇注系统,可以显著减少铸件夹渣.利用横浇道降低金属液的流动速度,延长渣粒的运动距离,促进渣粒上浮运动是提高浇注系统挡渣效果的关键.     

铝合金高压开关壳体铸造针孔形成原因及解决措施

铝合金高压开关壳体形状复杂,采用低压砂型铸造时,端面处有针孔缺陷。分析认为,针孔缺陷形成的原因是铸件内浇口设计在端面处,凝固时冷却缓慢,导致氢气析出,阻碍铝液补缩,形成气缩孔。通过对铸造工艺优化,加快壳体端面部位冷却速率,解决了铸件针孔缺陷。     

消除碳素钢精密铸件表面渣、气孔的措施

精密铸造生产中,碳素钢精密铸件因含碳量高,浇注过程中吸气、氧化严重,铸件表面容易出现渣、气孔,主要集中在组树方案中铸件的上表面,影响铸件的外观及质量.在常规方法不能完全解决的情况下,引入砂模铸造工艺设计方法,通过外加直浇道,钢水从外加直浇道中注入型壳,使钢水在型壳内平稳上升,产生的气及渣随同钢水通过内浇道顺利浮出铸件,避免组树方案中铸件上表面产生渣气孔,改善铸件表面质量,减少铸件后期的修补成本.     

Al—Mg合金铸件的夹杂物与过滤处理

一、绪言 铝合金在熔融状态容易生成氧化物,同时因吸收氢气,所以在铸件中容易产生氧化物和气孔等缺陷。这些缺陷,使铸件的机械性能恶化。因此,铝合金在熔化、铸造时,必须防止产生和卷入非金属夹杂物以及产生气孔。防止气孔的措施,过去曾采用除气和吹入气体除气的方法。最近,也有采用真空除气的。对于非金属夹杂物,过去采用熔剂防止氧化物的生成。现在去除铝合金中非金属夹杂物,作为重要课题提出来了,特别关注使用氧化铝颗粒、玻璃纤维网等过滤方法来去除溶液中的夹杂物。并正在研制各种各样的过滤装置。采用这种处理溶液的方法,不仅是提高溶液质     

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.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.