激光金属成形缺陷在线检测与控制技术综述

激光金属增材制造技术通过金属材料的激光逐层熔化堆积实现复杂零件的直接成形制造。激光金属成形零件易出现宏观缺陷以及内部冶金缺陷,严重影响零件的性能。综述了国内外激光金属成形零件宏观缺陷、内部冶金缺陷在线检测及缺陷控制技术的研究进展。分析指出目前普遍采用的熔池物理参数在线检测和反馈控制技术的主要作用是减少零件的宏观缺陷,但在消除内部冶金缺陷方面的作用是有限的。为了提高激光金属成形零件的关键力学性能,内部缺陷控制正逐渐成为激光金属成形领域新的研究热点。     

激光熔覆成形Ni基合金层的缺陷分析及控制

激光熔覆成形零件的质最控制和缺陷防止足目前该领域的研究热点和难点.本文以大量的激光熔覆成形实验为基础,系统总结了实验中易出现的各种缺陷,深入分析了各种缺陷的形成机理,提出了控制缺陷产生的应对策略,旨在为后续实验成形高质量金属零件、规避成形缺陷提供一定的理论依据.     

左纵梁中段冲压成形缺陷分析及解决方法

以左纵梁中段为研究对象,采用有限元软件Autoform对零件进行数值模拟,根据零件的成形特点,分析了左纵梁中段的成形缺陷,并总结了此类成形缺陷的解决方法。     

高强钢零件成形质量控制策略

介绍了高强钢在汽车车身中的应用现状,阐述了高强钢零件在冲压成形过程中的典型缺陷与形成机理。针对高强钢零件在成形过程中的典型缺陷,从零件设计、工艺设计、模具技术、现场调试等4个方面,对其成形质量控制措施进行了详细阐述,探讨高强钢零件的成形质量控制技术,对车身高强钢零件的设计与模具开发具有一定的参考作用。     

汽车前纵梁内板拉延成形数值模拟及工艺参数优化

针对板料冲压过程变形复杂,易出现起皱、拉裂等缺陷,以某型汽车前纵梁内板为研究对象,采用有限元软件DYNAFORM对零件拉延工艺进行了数值模拟仿真。针对零件成形特点,设计了合理拉延形面,并分析拉延筋、压边力及入模圆角的变化对该零件成形效果的影响。通过零件成形极限图优化拉延筋、压边力及入模圆角,最终获得适合该零件的成形工艺参数。试模结果表明,采用优化后的参数可有效改善材料流动状况,消除起皱、拉裂等缺陷,提高成形质量。     

AZ80镁合金底座预成形的数值模拟研究

利用DEFORM软件模拟了AZ80镁合金底座零件的成形过程.找出了缺陷,并分析了缺陷产生的原因.通过设计两种预成形方案,确定了消除缺陷的最终工艺.制定了零件的工艺过程,批量生产时有指导作用.     

变截面轴冷挤压成形数值模拟

借助于数值模拟技术,研究了变截面轴冷挤压成形过程,分析了零件不同部位金属流动填充特点及凸模载荷,并对零件成形过程的缺陷进行了预测.结果表明:金属流动顺利,没有成形缺陷.冷挤压工艺是合理可行的.     

基于Deform-3D在车轮螺栓成形设计中的应用

车轮螺栓成形属大料小变形的塑性成形,成形工艺与毛坯设计不合理,容易产生材料填充不足、成形的零件出现起皱和裂纹等缺陷,通过Deform软件的3D成形分析模块,能快速准确地预测车轮螺栓成形中可能出现的缺陷,优化预成形毛坯与工艺方案,以缩短研发周期,降低试模成本,对于类似零件的设计开发提供了参考。     

座垫衬板冲压成形性的有限元分析

针对某座椅衬板初步设计模型,分别采用一步法和增量法分析其冲压成形性能,发现局部存在起皱、破裂等成形缺陷.通过重新设计零件及模具形状尺寸.零件成形性能有了明显改善.这说明一步法与增量法相结合进行冲压成形过程数值分析,可以准确预测成形缺陷.提高零件及模具设计效率和质量.     

流线形拉深件冲压工艺分析及有限元数值模拟优化

利用Dynaform软件模拟流线形铝制品零件的拉深成形过程，得出冲压成形的FLD图，并优化板料形状和工艺参数避免产生缺陷。分析了成形工艺参数对成形质量的影响，制定了铝制品零件的冲压工艺方案。实际生产的产品无缺陷，满足质量要求。     

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.