半固态铸轧AZ91D镁合金板带的再加工组织性能

实验研究了半固态铸轧成形技术制备的AZ91D镁合金板带的再加工组织性能及特点。半固态铸轧实验是在自制的试验机上进行的,得到半固态铸轧AZ91D镁合金板带之后,分别进行冷轧、热轧和冲杯实验,加工后取样观察显微组织。实验结果表明,半固态铸轧的AZ91D镁合金板带材具有较好的加工性,最大冷变形可达到28%,热变形可达到47%。观察组织可见,横断面、纵断面固相颗粒在轧制作用下都有所变形,纵断面的变形更为严重,说明组织沿轧制方向塑性变形较大。     

半固态铸轧成形的工艺耦合研究

通过实验研究了AZ91D镁合金半固态铸轧成形的工艺耦合问题。在AZ91D镁合金半固态铸轧成形试验中发现,半固态制浆工艺和铸轧成形工艺既独立又密切相关;两个工艺的工艺参数都有比较大的选择范围;两个工艺的衔接可以是连续的,也可以是间断的;两个工艺在很大范围内相结合,都能顺利进行半固态铸轧过程,都可以得到半固态铸轧板带。因此半固态制浆工艺和铸轧成形工艺的耦合具有比较大的自由度,这有利于半固态铸轧成形技术的产业化推广。     

铸轧半固态镁合金组织特点

在试验室半固态铸轧试验设备上，进行了镁合金半固态铸轧试验，发现铸轧对半固态镁合金组织有显著的影响。铸轧前组织中初生固相颗粒形状不规则，有枝晶的痕迹；然而铸轧后组织中初生固相颗粒形状非常圆整，接近球形；铸轧对半固态组织具有圆整化的作用，可能是通过固液两相相对流动、摩擦消除尖角而圆整化，或者固相颗粒翻滚、破碎重叠合并而圆整化两种方式实现的。另外在不同的工艺条件下，半固态铸轧镁合金板带组织在表面和心部有不同的表现，厚板带显微组织会出现偏聚，即表面层是激冷微细等轴晶区，心部是半固态组织；而薄板带组织非常均匀，没有偏聚。     

半固态AZ31流变铸轧温度场数值模拟

利用有限元方法对AZ31镁合金在半固态双辊铸轧成形工艺中的温度场进行了数值模拟。分析了铸轧工艺参数(轧辊表面对流换热系数、浇铸温度、浇铸速度)对镁合金板带质量的影响。结果表明,在浇铸温度降低到897K时,在10000W.m-2 K-1换热系数下镁合金熔体完全凝固点的位置前移,影响镁合金板带的质量;而将铸轧时间延长到0.465s可以加强熔体和铸辊换热,使得出口区域中心温度达到凝固点。     

镁合金的双辊板带连续铸轧技术

综述了绿色环保材料镁合金的特点、适用范围及其加工方式,分析了镁合金双辊板带连续铸轧技术是镁合金加工的未来发展方向,并指出了存在的问题和挑战.     

双辊铸轧镁合金板坯微观组织特征

利用自行开发的镁合金双辊铸轧设备，通过镁合金铸轧工艺试验，制备出AZ31镁合金铸轧板坯。研究了双辊铸轧镁合金板坯显微组织特征及铸轧温度对板坯微观组织影响规律。结果表明，镁合金双辊铸轧板坯晶粒细小，均匀圆整，显微组织具有快速凝固和半固态组织特征；铸轧温度对板坯显微组织的影响显著，当铸轧温度为685℃时，镁合金铸轧板坯获得理想的显微组织。     

半固态镁合金铸轧试验研究

自行研究开发了一套半固态铸轧试验设备,利用该设备可以获得半固态浆料,并进行半固态铸轧成形。试验研究了AZ91D镁合金半固态铸轧成形过程,观察了样品的微观组织形貌。结果表明,镁合金半固态铸轧可以改善镁合金高温铸造的安全防护和镁合金变形困难需要较大变形力的现状。     

AZ91D镁合金半固态铸轧工艺因素对组织的影响

在实验室半固态铸轧试验设备上进行了镁合金半固态铸轧试验,研究了AZ91D镁合金半固态铸轧组织的影响因素。结果表明,搅拌速度、铸轧温度对半固态镁合金组织有显著的影响。过快过慢的搅拌速度都不利于半固态组织的形成,试验表明搅拌速度300 r/min最佳;铸轧温度从高到低,固相率明显从小到大。     

半固态镁合金连续铸轧过程的数值模拟

根据半固态镁合金连续铸轧工艺过程的特点,建立了二维不可压缩非牛顿流体流动与传热的耦合计算模型,并使用流体分析软件FLOW3D对连续性方程、纳维-斯托克斯方程及能量方程进行稳态求解。考虑到辊间半固态金属浆料流动特点及双辊的布置方式有利于保持熔池内的层流流动,选取层流模型来进行描述。最终获得了连续铸轧工艺过程的流场、温度场和固相体积分数的分布以及入口浆料温度、铸轧速度等工艺参数对铸轧过程的影响规律。模拟结果可以很好地对工艺参数进行优化,从而为半固态镁合金的连续铸轧工业化生产奠定基础。     

温度对AZ31镁合金半固态铸轧组织的影响

数值模拟和试验研究了不同温度下半固态铸轧AZ31镁合金的铸轧过程温度场和微观组织。结果表明,在不同的铸轧温度下,铸轧过程温度场不相同,要顺利进行铸轧就需要不同的冷却系统。铸轧温度从高到低,半固态固相颗粒明显从小到大,固相率也变大。特别是在623℃到620℃之间固相率较高,固相颗粒接近球形,是典型的半固态组织。     

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.