超高强度钢板冲压件的激光点焊性能

选取高强度硼合金钢板EN-10292-TL4225,采用先进的激光点焊连接技术,利用优化的焊接参数,实现了这种钢板的热成形超高强度冲压件之间的优质连接。对激光点焊接头做了金相试验和搭接试样拉伸试验,并利用扫描电镜对拉伸断口进行了研究和分析。结果表明,采用激光点焊工艺得到的点焊接头具有良好的力学性能,能满足实际生产的需求。     

AZ31B镁合金板料热拉深性能研究

通过实验研究了成形温度对AZ31B交叉轧制镁合金板料成形性能的影响。结果表明：随着温度的升高（T≤240℃）,镁合金板料的成形能力提高,在210-240℃时,AZ31B镁合金板料具有很好的拉深成形性能,为最佳成形温度范围。     

H3Cr5WMoV埋弧堆焊合金层的组织与性能

利用自动埋孤焊在Q235钢基材表面得到H3Cr5WMoV合金堆焊层，并对合金堆焊层进行了回火处理。比较研究了堆焊层在焊态和回火态的组织、硬度、耐磨性及抗热疲劳性能。结果表明，堆焊层组织为板条马氏体加残余奥氏体。回火态堆焊层的硬度和耐磨性同于焊态堆焊层，回火态堆焊层的抗热疲劳性能也好于焊态堆焊层。     

Cu Partitioning Behavior and Its Effect on Microstructure and Mechanical Properties of 0.12C-1.33Mn-0.55Cu Q&P Steel

Cu, as an austenitic stable element, is added to steel in order to suppress the adverse effects of high content of C and Mn on welding. Based on C partitioning, Cu and Mn partitioning can further improve the stability of retained austenite in the intercritical annealing process. A sample of low carbon steel containing Cu was treated by the intercritical annealing, then quenching process(IQ). Subsequently, another sample was treated by the intercritical annealing, subsequent austenitizing, then quenching and partitioning process(IQP). The effects of element partitioning behavior in intercritical region on the microstructure and mechanical properties of the steel were studied. The results showed that after the IQ process ferrite and martensite could be obtained, with C, Cu and Mn enriched in the martensite. When intercritically heated at 800 ℃, Cu and Mn were partitioned from ferrite to austenite, which was enhanced gradually as the heating time was increased. This partitioning effect was the most obvious when the sample was heated at 800 ℃ for 40 min. At the early stage of α→γ transformation, the formation of γ was controlled by the partitioning of carbon, while at the later stage, it was mainly affected by the partitioning of Cu and Mn. After the IQP process, the partitioning effect of Cu and Mn element could be retained. C was assembled in retained austenite during the quenching and partitioning process. The strength and elongation of IQP steel was increased by 5 305 MPa% compared with that subjected to QP process. The volume fraction of retained autensite was increased from 8.5% to 11.2%. Hence, the content of retained austenite could be improved significantly by Mn and Cu partitioning, which increased the elongation of steel.     

基于性能梯度分布的硼钢热冲压工艺对形状精度的影响

为探究性能梯度分布的热冲压零件的回弹机理,采用模具分区加热技术,对USIBOR1500P硼钢板进行U形件热冲压试验,并采用NDI三坐标测量仪PRO CMM3500分析了不同保压压力和模具温度下冲压件热区、冷区及过渡区的回弹规律,零件组织采用扫描电子显微镜进行观察。试验发现:随着保压压力的增大,热区、冷区和过渡区的回弹角均减小;随着模具温度的升高,冷区回弹角基本不变,热区和过渡区回弹角均减小,且过渡区的回弹程度在同样条件下比冷区和热区小。组织分析结果表明:马氏体组织越多回弹越大,贝氏体组织越多回弹越小。     

汽车内板用冷热冲压薄板成形性对比

因生产工艺不同,薄板坯连铸连轧所生产的0.8～3.0mm的热轧产品与传统冲压用冷轧产品存在着一定的差异。从材料的化学成分、力学性能、扩孔性能等方面与冷轧冲压薄板进行对比研究。研究结果表明,两种材料化学成分相近,热轧SPHE薄板因屈服强度过高,r值过小,致使成形性低于冷轧产品。与汽车用冲压材料要求对比结果表明,SPHE板满足汽车用板冲压要求,可在汽车内板采用热轧材料进行＂以热代冷＂冲压生产。     

汽车超高强钢防撞梁热成形试验

以汽车用超高强度钢22MnB5为研究对象,采用直接热成形工艺和间接热成形工艺进行汽车防撞梁成形试验。采用金相显微镜、显微硬度仪和万能拉伸试验机等分析测试手段对成形件的组织、力学性能进行了分析。探讨了直接、间接热成形工艺对成形组织及力学性能的影响。结果表明,成形件的微观组织为理想的板条状马氏体,抗拉强度达到1500MPa以上,硬度在450HV以上,完全满足生产要求,实际生产中可以根据情况选择合适的成形工艺。     

超高强度钢板热冲压及模内淬火工艺的发展现状

超高强度钢板热冲压技术是将板料热加工和淬火工艺相结合的一项较新的复杂成形技术。它使超高强度钢板具有较小的变形抗力、塑性好、成形极限高,而且成形零件的精度和强度较高。该技术生产的零件使汽车轻量化后仍能满足碰撞安全性能。介绍了超高强度钢板的种类及相应热冲压技术的关键技术,概述了热冲压技术实验研究及数值模拟研究的主要内容及其现状,并对热冲压技术存在的问题进行了评述,对未来发展的内容和重点研究方向进行了展望。     

防撞梁热冲压模具冷却系统的数值分析及优化

以防撞梁热冲压模具冷却系统作为研究对象,依据对流传热及流体原理,结合边界层理论对冷却系统传热进行分析,提出冷却系统设计方案,利用Fluent软件模拟模具冷却效果,优化冷却系统直至模拟结果满足要求并通过试验加以验证。结果表明在模具设计中,管道半径R越大,管道侧壁间距L、管道顶部至模面的垂直距离H越小,板料冷却速率越大,其中H对于模具冷却速率的影响较大,L对于最大温差影响较大。通过对R、L、H的选择与局部调整使板料在均匀冷却的前提下完成马氏体转变。此外,冷却系统的设计还需保证模具的结构强度以及长期工作中能够保持热稳定性。     

Forming limit of sheet metals based on mixed hardening model

The calculation method of forming limit of sheet metals based on M-K instability theory is proposed,and the method is applicable to different yield criterions and hardening models.The forming limit dia-grams of AA5754-O,AA6111-T4 aluminum alloy sheet and DP steel sheet under combined loading paths are obtained based on mixed hardening model with YLD2000-2D yield criterion proposed by Barlat in 2003 and L-C nonlinear kinematic hardening model proposed by Lemaitre and Chaboche.The results show that the formin...     

Influence of heating parameters on properties of the Al-Si coating applied to hot stamping

The Al-Si coating of ultra-high strength steel has been applied to hot stamping more and more widely, owing to solving the problem of oxidation and decarburization. However, the evolution of Al-Si coating during the heating process was rarely studied in the previous study. The tests about the influence of heating parameters, such as heating temperature, heating rates and dwell time, on properties of the Al-Si coating were carried out on the Gleeble-3500 thermal simulator. The properties of the Al-Si coating, for instance, volume fraction of FeAl intermetallics, α-Fe layer as well as porosity and 3D surface topography, were explored in the study. Results showed that more and more Kirkendall voids and cracks appeared in the Al-Si coating when the heating temperature exceeded 600°C. The heating rates almost had no influence on properties of the Al-Si coating when the temperature was equal to or lower than 500°C. The volume fraction of FeAl intermetallics in the coating with dwell time from 3 s to 8 min at 930°C was0, 6.19%, 17.03% and 20.65%, separately. The volume fraction of the α-Fe layer in the coating changed from zero to 31.52%with the prolonged dwell time. The porosity of the coating ranged from 0.51% to 4.98% with the extension of dwell time. The unsmooth degree of the surface of the coating rose gradually with the increasing of heating rates and the extension of dwell time.The 3D surface topography of the coating was determined by the comprehensive effect of atoms diffusion, new formed phases,surface tension and the degree of oxidation of the coating surface. Experiments indicated that rapid heating was not suitable for the coating when the temperature exceeded 500°C. Experiments also demonstrated that enough dwell time was essential to obtain the superior properties of the coating.     

Analysis of bending on the front end of sheet during hot rolling

The analysis of bending in finishing rolling was performed. An asymmetrical rolling force model was established, and the upper and lower neutral points were determined. Thc bending which resulted from the asymmetrical rolling force at the roll gap was studied and related flexibility equations were proposed according to elastic mechanics. Moreover, material mechanics was used to analyze the effects of temperature difference and self-weight on the bending out of the roll gap, and the flexibility equations were constructed. The main factors on bending were summed up, and the bending rule in the rolling could be obtained. In addition practical calculation was made with the production data of ribbon steel from Laiwu Iron ＆ Steel Group Co. Ltd.     

Effect of drawbead on forming performance of subsequent sheet

In order to research the plastic performance of sheet going through the drawbead and the simple tensile test of sheet, the influence of drawbead structure parameters on sheet performance and the subsequent performance of the sheet were performed to investigate the residual deformation characteristics of the sheet through different drawbead structures, and also the influences of drawbead structures and geometry parameters on pre-deformation and subsequent forming characters of sheet were analyzed. The results show that the pre-deformation decreases with the increase of the round corner radius, the pre-deformation increase with the increase of the height of drawbead, and the subsequent forming characteristics of sheet going through drawbead are remarkably different from undeformed sheet and these differences heavily depend on the pre-deformation. With the increases of pre-deformation, the yield ratio increases, but the subsequent elongation exponential decreases. These means deformability of the sheet is significantly reduced. As the structure of drawbead changes, the mechanical characteristics of material in different cyclic loading conditions also change. For the BUFDE+Z deep drawing steel sheet, the subsequent performance of the sheet is hardened when the pre-deformation is greater than 0.044. For the DC52D+ZF hot-galvanize steel sheet, the subsequent performance of the sheet begins to harden when the pre-deformation is greater than 0.079, and it presents that the pre-deformation is not bigger than 0.052.     

Research on technological parameters of pressure forming with hot granule medium on AA7075 sheet

Hot granule medium pressure forming(HGMF) process is a new process in which granule medium replaces the medium in existing flexible-die hot forming process, such as liquids, gases or viscous medium. Hot forming of light alloy sheet parts can be realized based on the properties of granule medium, such as withstanding high temperature and pressure, filling well, sealing and loading easily. In this work, the forming of AA7075 cylindrical parts by HGMF process is taken as an example to establish the constitutive relation and forming limit diagram(FLD) of AA7075 sheet which is related to temperature by hot uniaxial tensile test of sheet metal. Based on the assumption that granule medium is applied to extended Drucker-Prager linear material model, the finite element model of HGMF process is established and the effect of technological parameters, such as forming temperature, blank-holder gap and drawing ratio, on the sheet metal formability, is studied. The limit drawing ratio curve of AA7075 cylindrical parts at forming temperature of 175-300 °C is obtained by HGMF process test, and the limit drawing ratio reaches the maximum value of 1.71 at 250 °C. The results of numerical simulation are consistent with the results of process test, and the forming force, distribution of wall thichness and form of instability are predicted correctly, which provides reference for the application of HGMF process.     

基于柔性装配偏差模型的汽车车身薄板零件公差设计

基于汽车车身柔性薄板零件装配建模方法,建立柔性薄板零件公差优化设计方法。根据柔性薄板零件测点装配偏差与各偏差源间的确定性模型,综合得到测点装配偏差的方差与零件制造方差和夹具定位方差之间的模型,以零件测点平均方差为公差设计函数,工序能力指数和零件制造方差比为约束函数进行零件公差优化设计,并采用车身后地板装配进行应用分析。结果表明,搭接焊接结构的零件公差设计需同步进行,对接焊接结构零件公差设计各自独立进行,而角接焊接结构的零件公差设计则先进行其中对接零件公差设计,然后进行搭接零件公差设计;搭接焊接结构中零件间刚度差异比较大时,刚度小的零件公差可以取相对更大的公差。     

Enhancing ductility of the Al-Si coating on hot stamping steel by controlling the Fe-Al phase transformation during austenitization

In this study,austenitizing heat treatment before hot stamping of Al-10%Si coated boron steel is first investigated through environment scanning electron microscopy(ESEM)equipped with energy dispersive x-ray analysis(EDAX).The cracking behavior of the coating was evaluated using Gleeble 3500,a thermo-mechanical simulator under uniaxial plastic deformation at elevated temperatures.The extent and number of cracks developed in the coating were carefully assessed through an optical microscope.The coating layer under hot-dipped condition consists of an Al-Si eutectic matrix,Fe2Al7Si,Fe3Al2Si3 and Fe2Al5,from the coating surface to the steel substrate.The coating layer remains dense,continuous and smooth.During austenitization,the Al-rich Fe-Al intermetallics in the coating transform to more Fe-rich intermetallics,promoted by the Fe diffusion process.The coating finally shows the coexistence of two types of Fe-Al intermetallics,namely,FeAl2 and FeAl.Microcracks and Kirkendall voids occur in the coating layer and diffusion zone,respectively.The coating is heavily cracked and broken into segments during the hot tensile tests.Bare steel exposed between the separate segments of the coating is oxidized and covered with a thin FeOx layer.The appearance of the oxide decreases the adhesion of the Al-Si coating.It is found that the ductile FeAl is preferred as a coating microstructure instead of the brittle FeAl2.Therefore,the ductility of the Al-Si coating on hot stamping boron steel could be enhanced by controlling the ductile Fe-rich intermetallic phase transformations within it during austenitization.Experiments indicate that a higher austenitizing temperature or longer dwell time facilitate the Fe-rich intermetallics transformation,increasing the volume fraction of FeAl.This phase transformation also contributes to reducing the crack density and depth.     

织物增强混凝土薄板四点抗弯性能试验

为研究薄板四点抗弯性能,测试了织物的力学性能,同时配制了与织物性能相适应的高性能混凝土,对织物增强混凝土薄板抗弯性能进行测试.,用织物增强混凝土薄板,具有较高的抗弯承载力,同时具有良好的变形性能;其抗弯承载力与纤维织物的体积含量及是否浸胶有关;对织物施加预应力后,薄板的开裂荷载提高,裂缝宽度减小.并结合试验结果对织物增强效果作出理论分析.     

Microstructure and strengthening parameters of ultra—thin hot strip of low carbon steel

The microstructure and precipitation mechanism of ultra-thin hot strip produced by CSP technology were analyzed by electron back scattered diffraction(EBSD),H-800 transmission electron microscope(TEM) and thermodynamics theory.The EBSD results show that the finishing hot rolling microstructures are mixture of recrystallized and deformed austenite.After phase transformation,ferrite grains embody subastructures and dislocations that led ultra-thin hot strip high strength and relatively low elongation rate.TEM observations show that there are a lot of fine and dispersive precipitates in microstructures.Most of aluminium nitrides are in grains.While coexisted precipitates of MnS along grain boundaries,Coexisted precipitates compose cation-vacancy type oxides such as Al2O3 in the core,while MnS at the fringe of surface.At the same time,reasons for microstructure refinement and strengthening effect were invstigated.     

激光焊接650MPa相变诱发塑性钢的组织与性能

采用固体Nd:YAG激光器焊接拉伸强度级别为650MPa、厚度为1.2mm的相变诱发塑性钢(TRIP)薄板,利用光学显微镜和电子显微镜研究了其不同焊接速度下对接焊缝的形貌和组织特点。测试了接头的硬度和抗拉强度,借助杯凸试验对比研究了激光焊接接头和母材的成形能力,并分析了焊接速度对接头组织、性能的影响。研究表明:TRIP钢的相组成主要是大量铁素体、贝氏体和少量的残余奥氏体;激光焊缝金属则主要由马氏体构成。焊缝金属或焊接热影响区的近缝区具有最高的硬度。焊缝金属的屈服强度和抗拉强度在垂直于焊缝方向与母材基本相同,但在平行于焊缝方向明显高于母材。与母材相比,激光焊接TRIP钢薄板的冲压成型能力明显下降。     

c-BN仿生耐磨复合材料的微观结构和耐磨性能

采用SPS技术制备出多尺度的c-BN仿生耐磨复合材料,应用图像分析仪、SEM和XRD分析c-BN仿生耐磨复合材料的微观组织.研究结果表明,Cu基合金对c-BN单晶颗粒具有良好的润湿性能,界面结合致密,在界面处形成反应层.微观分析表明,Cu基合金中的Ti向c-BN单晶颗粒表面富集,并与N和B元素发生作用,形成TiB2和T...