压铸件缺陷特征及其防止措施

分析了压铸件气孔、缩松、夹杂、冷隔、尺寸超差及表面质量问题等缺陷特征,从模具设计、熔炼工艺及涂料使用等方面对缺陷产生的原因进行了探讨。结果发现,在合理的零件结构基础上,通过改进浇注系统,调整模具温度及金属液温度,并采用正确的喷涂方法,可有效防止压铸件缺陷的产生。     

铝合金压铸件缺陷及模具分析

针对压铸件出现的拉伤、气孔、冷隔及粘模等各种缺陷,从力学、热力学、流体动力学角度,分析讨论了压铸模设计及压铸件产生质量问题的原因,为改进模具指出了明确方向。     

4.8L发动机飞轮壳气孔和冷隔产生的原因及解决措施

4.8 L发动机飞轮壳铸件废品率高达10％以上,产品缺陷主要表现形式为气孔和冷隔.针对存在的问题,对该产品进行工艺分析,制定了改进方案,新工艺方案试验验证后,解决了飞轮壳气孔、冷隔等高废问题.     

滑动梁铸件铸造工艺改进

针对铸件易出现冲砂、砂眼、气孔和冷隔等缺陷,导致废品率高的问题,对原有的生产工艺进行了改进,包括浇注系统和冷铁位置、工艺装备及严守操作规程等。改进后的工艺方案,减少了冲砂、砂眼、气孔和冷隔等缺陷,保证了产品的质量,废品率降低到4%以下。     

复杂离合器壳体压铸缺陷的工艺研究

以一种复杂离合器壳体压铸件为研究对象,分析压铸件局部区域存在拉伤、冷隔等缺陷的原因,提出合理的解决方案,对压铸参数进行优化,达到批量生产的目的。结果表明,通过工艺参数的优化可以有效地减少产品的拉伤和冷隔,提高产品质量。     

压铸镁合金件冷隔缺陷的分析及对策

冷隔缺陷是镁合金压铸常见缺陷之一,对产品的品质及使用性能产生严重影响。以齿轮室镁合金压铸件为例,从合金原材料、压铸工艺参数及模具设计3个方面分析了冷隔产生的原因,并提出了改进措施。经过生产验证,效果良好。     

铝合金壳体的压铸工艺优化设计

根据壳体压铸件的结构特点,进行了压铸工艺设计,主要包括选定分型面、浇注位置及工艺参数,计算浇注系统各截面尺寸,同时借助华铸CAE软件模拟压铸件的充型过程来确定溢流槽的位置、数量及尺寸等,设计的压铸工艺经生产验证,能够满足压铸生产需要,生产的壳体铸件没有出现异常气孔、冷隔、浇不足、缩孔等铸造缺陷。     

4H11V16缸体铸件缺陷分析与工艺改进

4H11V16缸体铸件在小批量试制的过程中,废品率较高,使产品的合格率在77%左右一直无法有效提升。通过对缸体的制芯工艺、排气设计、组芯过程等方面进行深入的研究,并结合现场调查与计算机模拟分析,找到了原铸造工艺出现断芯、气孔、冷隔这三种主要缺陷产生的原因。采取了相应的改进措施：（1）通过调整砂芯配合间隙并对组芯工艺进行验证,同时开展水套芯刷涂料试验,解决了水套芯断芯的的问题;（2）通过优化砂芯烘干工艺、增加砂芯及型腔的排气通道、砂芯局部掏空等措施解决了气孔缺陷;（3）通过改进浇注工艺、增加集冷冒口等措施,使冷隔缺陷得以解决。工艺优化后,缸体铸件综合成品率由77%提升至94%以上。     

压铸铝合金汽车前罩壳缺陷分析与工艺改进

分析了铝合金压铸件前罩壳产生气孔、缩孔的原因,缺陷主要是工艺不完善造成的。增加渣包,解决了零件中央密封槽的气孔缺陷;增加挤压销,解决了M6螺孔的缩孔缺陷。工艺改进后的生产实践表明:中央密封槽的气孔缺陷比例小于0.5%,气孔大小由准φ3mm减小至准φ0.5mm,螺孔的缩孔缺陷为零。     

压铸铝合金汽车油底壳缺陷分析与工艺改进

通过对发动机铝合金油底壳压铸缺陷的分析,引入模流分析技术改进浇注系统设计,采用超点冷技术处理螺孔缩松问题,利用端面打点技术处理气孔问题,有效地解决了产品的裂纹、缩孔、缩松、气孔缺陷,使产品的压铸合格率由70％提升到95％,工艺改进获得成功.     

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.