不锈钢搅拌桨的精密铸造

研究了小型框式薄壁不锈钢搅拌桨的精密铸造工艺.利用无余量整体精密铸造成形技术,通过对工艺参数的合理设计和优化,减少了铸造缺陷,提高了合格率,生产出了表面质量高、尺寸精度高、附加值高的产品.     

微精密铸造工艺研究进展

三维复杂形状的金属微构件的微细加工一直是微机械研究的重点和热点，近年来涌现出许多的加工工艺，比较而言，微精密铸造工艺在高效制备三维复杂形状的微构件方面具有十分独到的优势。文中从微精密铸造工艺、合金、铸型材料及相关理论等几个方面综述了国外基于熔模铸造的微精密铸造工艺的发展现状，并讨论了现有微精密铸造工艺的不足，提出了微精密铸造工艺的发展方向，同时，对作者在金属型微精密铸造工艺方面的研究作了简要的介绍。     

熔模精密铸造技术在航空工业的应用及发展

概述了熔模精密铸造技术的工艺特点及基本制作流程,对近年来熔模铸造技术在国内外航空工业上的应用情况做了说明。按照不同合金的熔炼及成形特点,介绍了铝合金精密铸造技术、镁合金精密铸造技术、钛合金精密铸造技术与高温合金精密铸造技术在航空武器装备上的应用及典型构件的制备。说明了各合金精密铸造技术的新型特种铸造方法、特种型芯技术、计算机工艺辅助与数值仿真以及特种成形设备与工艺等关键技术的最新研究进展情况,并阐述了航空工业精密铸造技术未来的研究热点与发展方向。     

SLA快速精密铸造技术应用现状分析

在介绍了SLA快速成型的基本原理和快速精密铸造工艺方法的基础上,论述了几种用于精密铸造工艺上的SLA快速成型工艺、特点和存在的问题,并做了简要分析,为铸件的快速精密铸造打下良好基础。     

用快速精密铸造工艺铸造叶轮发泡模具

开发了一种叶轮发泡模具的快速精密铸造工艺.在铸造工艺中,利用快速成型技术和复合陶瓷型壳技术来制备叶轮的精密铸造型壳.用该铸造工艺铸造的叶轮发泡模具具有尺寸精度高、表面光洁度好的特点,可满足叶轮发泡模具的使用要求.     

我国熔模精密铸造的历史回顾与发展展望

概述了熔模精密铸造的特点及在我国的整体发展现状。按照不同产品类别追溯了我国熔模铸造发展的历史、技术进展、行业现状。详细介绍了通用硅溶胶型壳工艺、钛合金熔模铸造工艺、铝合金熔模铸造工艺、石膏型熔模铸造工艺、水玻璃型壳工艺等多种工艺方法以及熔模精密铸造在航空、航天以及一般商用铸件上的应用。指出了我国熔模精密铸造与工业发达国家之间存在的差距,并对我国熔模精密铸造行业的发展提出了几点建议。     

半精密铸造方法的探索与实践

为解决形状复杂、壁薄、尺寸小、表面质量要求高的铝合金铸件快速制作的问题,运用消失模铸造和石膏型铸造相结合的技术,通过实验开发了一种铝合金壳体铸件的半精密铸造工艺.基本方法是:先将泡沫模型组合造型,再以其为模样进行石膏型制作,然后用铝合金对石膏型浇注.结果表明,利用此法实现了对小型复杂薄壁铝合金铸件的半精密铸造.     

精密铸造导卫H13钢显微组织分析

研究精密铸造导卫H13钢在不同热处理工艺下的组织结构性能,制定了该钢最佳热处理工艺,使其性能获得提高,并应用于轧制线材轧机导卫上.结果表明,精密铸造H13钢在加热温度为870～890℃,以20～30℃/h的冷却速度退火时,硬度最低;最佳淬火温度为1 050℃,淬火后应进行2～3次回火,可以获得高的热稳定性、强韧性和热疲劳性能.     

熔模精密铸造型砂的煅烧工艺

安徽淮北矿区煤系高岭土资源丰富,矿石纯度高、结晶有序度好,适合做熔模精密铸造用砂、粉产品.作为精密铸造型壳背层耐火材料,煅烧工艺对耐火材料的质量起主要作用.通过严格控制煅烧过程中回转窑的负压、燃料火焰调节、煤质等几个方面,生产出了质量好,性能稳定的精铸砂、粉产品,在铸造生产中得到了广泛应用.     

铸造CAE技术在熔模铸造中的应用

介绍了铸造CAE技术的基本思路和原理;并给出了华铸CAE软件在熔模铸造中的一些应用实例,应用表明现阶段的铸造CAE软件能够准确地预测熔模精密铸件在充型凝固过程中可能产生的缺陷,从而辅助工艺人员进行工艺优化,指导实际熔模精密铸件生产.     

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).     

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.     

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.     

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.