高含量Sip/Al复合材料的无压浸渗机制

采用无压浸渗工艺, 制备出高含量Sip/Al复合材料. 对无压浸渗过程进行了静力学分析, 对无压浸渗机制进行了研究, 并采用电阻法对Al液无压浸渗Si松装多孔体的动力学过程进行了实时测量. 结果表明: Al液浸渗Si多孔预制体符合浸渗静力学条件, 其实际浸渗过程符合抛物线关系. 组织观察结果表明, Si相呈网络状连续分布, 其形成机制主要为浸渗时Si颗粒的溶解-析出机制和凝固过程中Si的附着析出机制. 组织中存在少量的孔隙. 复合材料的界面清洁平整, 未发现有反应物存在.     

电磁搅拌对铝硅合金显微组织的影响

研究电磁搅拌对亚共晶、共晶及过共晶Al—Si合金显微组织的影响，并对其在EMS作用下的液淬组织和凝固组织进行研究。试验表明：电磁搅拌能够改变正常的铝硅合金凝固行为。本试验条件下EMS作用下非树枝晶存在异常长大、聚集和缩颈熔断现象；对亚共晶Al-Si合金凝固主要表现为共晶组织发生粗化；对过共晶Al-Si合金凝固主要表现为初生硅的聚集与偏聚。     

电脉冲对Al-12.5%Si合金的孕育变质效应

研究了Al-12.5％Si合金液存在较大过热度的情况下，电脉冲处理对其凝固组织中初晶相和共晶相的影响。研究发现，经电脉冲处理后的共晶Al-Si合金凝固组织中出现了过共晶组织中才应出现的初晶硅，α-Al枝晶长度变短；差示扫描量热法（DSC）曲线发生变化，电脉冲处理后有明显的初晶硅析出拐点，并且过冷度减小。理论分析表明，电脉冲处理促进了铝硅合金液中Si相的形核与长大，对Al-Si熔体的液态结构产生了影响，从而使其凝固过程和凝固组织发生变化。     

B_4C/Al-Si复合材料的制备

采用真空无压烧结法,制备了多孔碳化硼(B4C)骨架,致密度为46.8%.然后采用真空无压浸渗法,以A356铝合金为渗体,与B4C骨架进行复合.制备了B4C/Al-Si复合材料,致密度达99%以上,抗压强度为453 MPa,弯曲强度为294 MPa.微观结构分析结果表明,制备的复合材料组织致密,形成的Al、Si、Al3BC相分布均匀,界面复合良好.Al主要分布在B4C颗粒间,Si相主要分布在B4C和Al的界面处,使B4C和Al紧密结合,且试样的表面和心部均有分布均匀的Al存在.制备的B4C/Al-Si复合材料中B4C形成连续的骨架结构,而孔隙处的金属相则起到增韧、增强的作用.     

快速凝固过共晶Al-Si合金的显微组织及其热稳定性

采用扫描电镜(SEM)、差热分析仪(DSC)和X射线衍射仪(XRD),分析快速凝固过共晶Al-Si合金粉末显微组织和结构特征及其在不同退火温度和保温时间条件下过饱和固溶Si元素析出和Si相粗化行为。结果表明:快速凝固Al-Si合金显微组织中细小的块状初晶Si相和针状共晶Si相均匀分布在α(Al)基体中;气雾化过程获得的高过冷度导致Al基体晶格发生畸变,其在退火过程中得到一定程度的缓解。对快速凝固Al-Si合金中析出Si相粗化行为的分析发现,析出Si相随退火温度升高或保温时间延长而不断粗化;但其粗化不符合经典LSW理论(粗化指数n为3),粗化机制接近由扩散速率较快的界面扩散控制(n接近2)。此外,退火温度仅对粗化速率常数和激活能有较大影响,而对粗化指数的作用不明显。     

压力浸渗制备具有优异变形能力的Ti-Al复合体(英文)

采用压力浸渗法成功制备网状结构的Ti-Al复合体,使用OM、XRD、SEM以及能谱仪对制备的Ti-Al复合体进行组织观察与分析。采用共晶Al-Si合金代替纯Al可有效降低压力浸渗所需温度,降低液态Al与Ti颗粒表面接触而发生的非扩散控制反应的剧烈程度。反应层厚度控制在3μm左右,最先反应产物为TiAl3相。压力浸渗时,Ti原子溶于Al-Si液相及Si原子向Ti颗粒表面富集使得在反应层外侧及Ti-Al复合体Al相中形成TiSi2Al相。挤压变形组织显示制备的Ti-Al复合体具有优异的变形能力。     

Al-Si共晶对Mg-12Li合金组织及性能的影响

对比分析了添加Al和Al-Si共晶的Mg-12Li合金铸态及轧制态的组织和性能,研究Al-Si共晶对合金组织性能的影响。结果表明,当加入Al-Si共晶后,Mg-12Li-3(Al-Si)组织中开始有白色析出物(脆性相Mg2Si)析出,形成的中间化合物依次为Al Li、Mg Li2Al、Mg2Si。该合金抗拉强度为230 MPa,伸长率为25.5%,性能接近添加了RE的镁锂合金,成本得到明显的降低。当Al-Si共晶量达到6%时,合金的力学性能会下降。     

固溶处理对快速凝固过共晶铝硅合金组织性能的影响

利用单辊旋转甩带法制备快速凝固铝硅合金薄带,并对其进行固溶处理,研究了不同固溶热处理工艺对合金组织和性能的影响.结果表明,快速凝固使Si相的形核和析出受到抑制,α相领先析出;与铸态组织相比,过共晶成分的铝硅合金经快速凝固后得到微纳米级亚共晶组织,且在随后的固溶处理过程中,随着保温时间的延长,Si元素从基体中脱溶析出并逐渐聚集长大,形成细小的Si颗粒均匀分布于基体之上.在480℃下保温100 min并水淬,经自然时效96 h后,Si相颗粒细小且圆整度高,合金硬度(HV)达到最高值241.67.     

铝合金热浸镀Zn-xAl合金凝固组织研究

在本研究中使用Zn-xAl合金液对铝合金表面进行热浸镀,重点研究不同Al含量的Zn-xAl合金液在坩埚中凝固的铸锭组织及在铝基体表面凝固的镀层组织中共晶形貌,分析了不同冷却条件下共晶组织的形成机理及影响因素。结果表明,Zn-xAl合金液铸锭由于冷速较低,属近平衡凝固,共晶组织为典型的片层结构;Zn-xAl合金液镀层的凝固由于冷速过快,冷却速度成为共晶结构的决定因素,共晶组织为非规则共晶形貌,α富Al相呈球形、椭球形或短棒状组织。试验中不同冷却条件下,Zn-xAl合金共晶析出时其领先相均为β富Zn相。     

Al-Si共晶对Mg-12Li合金微观组织及性能的影响

对比分析了添加Al和Al-Si共晶的Mg-12Li合金铸态及轧制态的组织和性能,研究Al-Si共晶对合金组织性能的影响。结果表明,当加入Al-Si共晶后,Mg-12Li-3(Al-Si)组织中开始有白色析出物（脆性相Mg2Si）析出,形成的中间化合物依次为AlLi、MgLi2Al、Mg2Si。该合金抗拉强度为230 MPa,伸长率为25.5%,性能接近添加了RE的镁锂合金,成本得到明显的降低。当Al-Si共晶量达到6%时,合金的力学性能会下降。     

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.     

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.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

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.