铸造工艺参数对超高强铝合金低频电磁半连续铸锭微观组织的影响

采用低频电磁铸造技术(电磁场频率为25 Hz,安匝数12 800 AT),按照不同的铸造工艺参数半连续铸造制备了直径为0.1 m的超高强度Al-12%Zn-2.5%Mg-2.5%Cu-0.15%Zr合金锭坯,考察了铸造温度、铸造速度和冷却水强度对铸锭组织的影响.结果表明,铸造温度为710℃,铸造速度为100 mm/min,冷却水强度为0.05 m3 /min时的低频半连续铸锭组织均匀细小,呈现近球形,边部和中间部位的晶粒大小差别较小,其平均晶粒尺寸分别为28μm和29μm.     

功率超声作用下水平连铸装置的设计及试验研究

为了提高水平连铸坯的使用性能，设计了一套带有功率超声系统的线坯水平连续铸造装置，并选择键合线用Al1Si合金作为试验材料在此装置上进行了模拟试验。采用光学显微镜分析了所得到的铸坯凝固组织，观察了铸坯的表面质量，并且对铸坯进行了力学性能测量。结果表明，功率超声作用下，铸坯的凝固组织得到细化，表面质量得到改善，当经功率为1000W的超声波处理后，合金抗拉强度和伸长率分别比未超声处理的合金提高了20．5％和37．5％。     

制备参数对HCCM水平连铸纯铜板坯组织与力学性能的影响

采用热冷组合铸型(HCCM)水平连铸制备横断面尺寸70 mm×10 mm(宽度×厚度)具有强轴向取向柱状晶组织的纯铜板坯,研究工艺参数对纯铜板坯微观组织、表面质量与力学性能的影响。结果表明:在铜液铸造温度1250℃,热型段温度1100~1150℃,冷却水流量600 L/h、连铸拉坯速度20~80 mm/min条件下可以制备出表面粗糙度低、具有沿拉坯方向强取向组织和优良力学性能的纯铜板坯,其抗拉强度为137~141 MPa,断后伸长率为45.1%~61.7%。随着拉坯速度的增加,HCCM水平连铸所制备纯铜板坯的组织均匀性增加,晶粒尺寸变小;热型段温度升高时板坯的柱状晶组织的晶界更加平直;而总体上力学性能受拉坯速度和热型段温度的影响较小。采用HCCM水平连铸,在热型温度为1150℃时制备的纯铜板坯的表面粗糙度小于0.3μm,无需进行铣面可直接进行后续冷加工,可为发展铜板带短流程生产工艺奠定基础。     

铸造参数对半连续铸造7050铝合金板坯质量的影响

从铸造速度、铸造温度、冷却水量、合金成分以及铸造液位高度几个方面着手,系统研究了铸造工艺参数对电磁半连续铸造7050铝合金板坯质量的影响,并深入分析了影响机理,摸索出了行之有效的铸造工艺参数.最佳工艺参数为:铸造速度85mm/min,铸造温度710℃,冷却水流量3m3/h,输入电流2 500A,频率1 700Hz,金属液面高度控制在石墨结晶器高度的1/2处.采用该工艺参数,成功铸造出尺寸为420mm×130mm×1 000mm的7050铝合金板坯.     

EMS-DC法制备的半固态ZL101A铝合金的组织与性能

研究了EMS DC法工艺参数对半固态ZL1 0 1A合金组织的影响 ,阐明了浇注温度 (中间包温度 )、拉坯速度、冷却速度与合金组织形貌的关系。研究表明 :在 0 .0 8～ 0 .0 9T的磁感应强度作用下 ,当铝合金在固液两相区的冷却速度小于 0 .3℃ /s时 ,即能得到较理想的非树枝晶组织。在优化各工艺参数的基础上 ,形成了半固态ZL1 0 1A合金的水平半连续铸造中试生产技术 ,其连铸坯铸态和热处理态强塑性综合指标分别为 430 .4和 497.4。     

无氧铜水平连铸液穴深度与浇注温度关系研究

在连续铸造过程中,铸坯液穴深度受冷却水量、拉坯速度及浇注温度等工艺参数的影响,掌握其影响规律对提高铸坯质量有显著帮助。本文通过ProCAST软件对100 mm×10 mm规格无氧铜方形铸坯的水平连铸进行研究,探究液穴深度与浇注温度之间关系。分析结果表明:浇注温度对液穴深度有一定影响;提高浇注温度可以使液穴深度加大,增大铸型温度,从而减小铸坯的温度梯度,降低其热应力;无氧铜水平连铸液穴深度与浇注温度呈线性关系,浇注温度越高,液穴深度越大。     

电磁连铸和微合金化对5356铝合金组织性能的影响

研究了不同电源功率、拉坯速率和冷却水量等参数以及微量Sc元素对5356铝合金组织和性能的影响。结果表明,在电源功率10 k W,拉坯速率8 cm/min,冷却水量1.7 m3/h的工艺条件下,5356铝合金具有最优的表面和内部质量以及综合力学性能,抗拉强度、伸长率分别可达310.0 MPa和16.3%,且铸锭表面无明显铸造缺陷,边部组织基本为等轴晶,心部组织呈破碎枝晶形态,第二相分布均匀。5356铝合金合理的均匀化处理工艺参数为440℃,30 h,空冷,均匀化处理后合金元素Mg的微观偏析基本消除,在晶界连续分布的Al8Mg5相明显回溶。微量的Sc元素显著提高5356铝合金的强度和塑性。实验证明,5356Al+0.4%Sc(质量分数)合金晶粒明显细化,第二相数量减少,抗拉强度和伸长率达330.0 MPa和29.0%,分别提高6.5%和77.9%。     

不同工艺热挤压后Mg-3Al-2Sc合金的组织与性能

采用不同挤压工艺对均匀化退火后的Mg-3Al-2Sc合金进行了热挤压实验,分析了挤压态Mg-3Al-2Sc合金显微组织及力学性能的变化.结果表明:在挤压温度380℃、挤压速度50mm/min下,挤压态Mg-3Al-2Sc合金可获得均匀的再结晶组织和良好的力学性能.挤压温度降低至350℃,强度明显提高,塑性降低,但挤压速度提高至70 mm/min,强度和塑性都降低.并且,经350℃、50 mm/min工艺挤压后,Mg-3Al-2Sc合金的拉伸断裂为沿晶断裂与准解理断裂的混合断裂,提高挤压温度可显著降低合金的沿晶断裂倾向.     

功率超声对水平连铸Al-1%Si合金凝固的影响

研究了水平连铸过程中在保温炉内施加功率超声熔体处理对Al-1%Si合金凝固过程的影响.结果表明施加功率超声后,合金凝固曲线第1个拐点左移,斜率发生了变化,且随着超声功率的增加,合金的结晶温度升高,当超声功率为1000W时,结晶温度提高了33℃;同时,施加了功率超声后,保温炉内金属液温度分布均匀性随着超声功率的增加得到了显著的改善;金相分析表明,当超声功率为1000W时,铸坯凝固组织得到了细化,同时晶粒尺寸更加均匀;此外,施加功率超声处理后铸坯表面质量得到了提高.     

基于遗传算法的铝铅系轴瓦连铸工艺优化研究

研究在Al-Pb钢背轴瓦连铸工艺系统中,通过遗传算法进行工艺优化的方法.确定了一组优化的工艺参数:连铸速度24.0 mm/s、冷却水流量350.0 mL/s、轧制铝厚0.24 mm、合金层厚度4.7 mm.实验表明,在此工艺条件下获得的Al-10%Pb合金组织中,球状的铅相颗粒分布均匀、平均直径<13μm;Al-10%Pb-钢背轴瓦材料有较好的过渡层,并具有较好的力学性能.抗拉强度为60 MPa、伸长率为17.2%,与轧制复合Al-20%Sn-1%Cu合金相近,Al-10%Pb合金层与钢背的剪切强度104.8 MPa,为轧制复合轴瓦Al-20%Sn合金层与钢背剪切强度的两倍.     

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.