金属薄板滚压冲裁过程数值模拟及模具参数

研究了在没有压下辊的情况下滚压冲裁过程的运动学特性,据此提出了通孔滚压冲裁模具的设计方案.在此基础上,利用ABAQUS有限元软件进行了基于Shear Failure韧性断裂准则和任意拉格朗日一欧拉自适应网格技术的45号钢薄板滚压冲裁过程有限元仿真,分析了主要参数对断面质量的影响.仿真结果表明:方形孔滚压冲裁时,前后刃口依次经历板带弯曲、凸模压入、裂纹产生和发展、断裂和凸模拔出五个阶段;滚压冲裁断面的主要质量缺陷包括断面垂直度、毛刺、塌角、压痕等;影响滚压冲裁断面质量的主要因素包括侧隙、凸模高度、辊子半径等.减小标称侧隙和凸模高度、增大辊子半径均会使断面质量提高,其中又以对断面垂直度和毛刺高度的影响更为明显.对于45号钢一类的碳钢,后刃口标称侧隙以板厚的5%-10%为宜,前刃口标称侧隙可以更小:辊子半径应以大于板厚的100-150倍为宜;在保证板材完全断裂的前提下,应使凸模高度尽量减小.     

Microstructural control in an aluminum core alloy for brazing sheet applications

The use of aluminum alloys for automotive heat exchangers has increased considerably in the last 15 to 20 years, and in parallel, new alloys have been developed to meet the increased demand for higher strengths and improved corrosion resistance. An Al-Mn alloy, X800, has been developed by Alcan to significantly increase the corrosion resistance of radiator tubes when subjected to typical service environments. Conventional alloy tubes, 3xxx or 6xxx, fail by intergranular attack, whereas X800 utilizes the diffusion of Si during brazing to form a sacrificial layer between core and cladding and thus prevent penetration through the core. The Si penetrates up to a depth of 70 μm into the core alloy and combines with both the Mn in solid solution and the coarse constituent particles to form theα-AlMnSi phase. In contrast to the core, the interface layer exhibits a high dispersoid density, a modified coarse particle chemistry, and a lower Mn level in solid solution after brazing. Three layers remain after brazing; anα-Al residual cladding, the interface layer with a band of dense precipitates (BDP), and the X800 core. Free corrosion potential measurements confirmed the lowering of the potential within the BDP by about 30 mV compared to —710 mV for the brazed X800 core.     

Microstructural and failure characteristics of metal-lntermetallic layered sheet composites

A processing technique for the fabrication of layered metal-intermetallic composites is presented, in which a self-propagating, high-temperature synthesis reaction (SHS) was initiated at the interface between dissimilar elemental metal foils. The resultant composite microstructure consisted of a fully dense, well-bonded metal-intermetallic layered composite. In this United States Bureau of Mines study, metal (Fe, Ni, or Ti) foils were reacted with Al foils to produce metal-metal aluminide layered composites. Tensile tests conducted at room temperature revealed that composites could be designed to behave in a high-strength and high-toughness manner by altering the thicknesses of the starting elemental foils. Failure characteristics revealed that the processes that govern ductilevs brittle behavior of the composites occur early in the fracture.     

Robustness of the sheet metal springback cup test

The robustness of a proposed test for elastic springback characterization of sheet metal has been examined using a matrix of defined experimental errors. A series of flat bottom deep drawn cups made from AISI 1010 steel sheet were examined. It was found that misalignment of the blank over the forming tool and error in the vertical location where the springback ring was cut from the cup sidewall had the largest effect on the resulting springback opening. Other experimental errors involving cup height and ring width were found to be less important. The effect of in-plane anisotropy of mechanical properties on springback was negligible. The results are examined in terms of measured through thickness residual stresses and elastic bending of beams with circumferential thickness gradients.     

镀层用热轧高强度结构钢板Q460DC的开发

通过对钢板化学成分、生产工艺、组织结构、力学性能、热镀锌性能和焊接性能进行研究,开发出镀层用热轧高强度结构钢板Q460DC。实际应用表明,该钢板综合性能良好,可满足热镀锌钢板塔制造的要求。     

Secondary work embrittlement of cold-rolled 05CuPCrNi sheet at low temperature

Due to the rapid development of China's rail transportation equipment manufacturing industry and related international distribution,important material suppliers such as Baoshan Iron Steel Co.,Ltd.carries on investigating the stability of material under extremely cold conditions.In this study,mechanical properties and secondary work embrittlement of weathering steel 05 CuPCrNi were tested at low temperature.Compared to the mechanical properties at room temperature,the yield and tensile strength increase slightly with decreasing temperature.However,the variation of elongation is not obvious.The experimental results also show that the secondary work embrittlement transition temperature of 05 CuPCrNi is lower than-60 ℃.These results provide the basis for the use of this train body material in extremely cold regions.     

金属薄板的氢扩散试验

 金属板材氢扩散计算试验选用材料为40Cr及4Cr13轧制板材,运用电化学方法进行氢扩散试验。通过对薄板进行表面处理,且进行预镀镍及镀镍的处理,最终进行氢扩散系数的测定试验,并根据氢扩散试验得到的数据参数进行氢扩散系数的计算,最终得到两种钢的氢扩散系数。氢扩散计算试验适用于各种不同金属材料氢扩散系数的测定,为检测钢在使用过程中氢的积累提供基本参数及计算依据,且对于材料中氢的定量计算起到至关重要的作用。通过对两种材料成分及扩散系数的比较,进一步研究金属中合金元素质量分数对氢在金属中扩散的影响作用。     

Strain localization in the diffuse neck in sheet metal

The onset of diffuse instability in sheet metals is associated with initially small, but grad-ually increasing, changes in the strain rate,é, and in the ratio of the minor to the major principal strains,p = ε₂/ε₁in the plane of the sheet. The hardening and softening contri-butions from such changes have been considered to obtain a condition for partial flow sta-biliity in the neck. The effect of the change inè on the uniaxial stress was determined from measurements of ε changes in the neck and from the strain rate sensitivity of the materials. Similar evaluation of the change in the axial stress due to a change in p was made by means of an approximate analysis. The combination of these effects, along with the basic strain hardening of the materials, is used to explain the slowness or the rapid-ity of the process of necking in several materials, exhibiting different normal anisotropy, strain hardening and strain rate hardening behaviors. These results can also be used to explain the size of a diffuse neck and the strain distribution within it. Correlation has also been obtained between necking extensions to failure and the forming limits.     

Microstructural investigation of a rapidly solidified 12Cr-Mo-V steel

Rapidly solidified martensitic stainless steel (11.59Cr-0.98Mo-0.28V (in wt pct) ribbons have been produced by the melt-spinning process. The microstructure of the ribbons showed three distinct zones: a columnar, a cellular, and a cellular-dendritic zone. The height of the columnar grain zone is independent of the process parameters such as the wheel material or the wheel velocity. Due to a high level of undercooling and a high growth velocity of the solid/liquid interface, the rapid solidification process is found to suppress the formation of δ-ferrite and enhance the formation of austenite. The austenite is transformed into martensite upon cooling. In comparison with conventional solidification, a reduction in the initial austenite grain size has been found to result in a very fine lath martensite (M) structure. Investigations of the texture within the ribbons along the growth direction show a weak fiber texture. Transmission electron microscopy (TEM) has revealed a [111]_M1 ‖ [001]_M2 and (011)_M1 ‖ (110)_M2 orientation relationship between two neighboring martensite laths. The observed orientation relationship is a result of a superposition of both the Kurdjumov-Sachs (K-S) and Nishiyama-Wasserman (N-W) orientation relations.     

Microstructural investigation of the oxidation of an Fe-3 pct Cr alloy

The microstructure and microchemistry of the oxide scale on an Fe-3 wt pct Cr alloy have been investigated after oxidation in the temperature range 700 to 800 °C. Transmission and scanning electron microscopy along with energy dispersive X-ray analysis and Auger electron spectroscopy techniques were used for the investigation. Multilayered scales are observed which vary in composition and structure; the innermost oxide is an Fe-Cr spinel of the type Fe(Fe_2•xCr_x)O₄. The intermediate layer and the outer oxide layer are both α-Fe₂O₃ hematite. The outer hematite layer is nonadherent and wrinkling is observed. Spallation occurs readily at the inner hematiteJspinel interface and at the spinel oxideJalloy interface. The poor oxidation resistance of the alloy is discussed in terms of these observations.     

Analysis of ridging in aluminum auto body sheet metal

A finite-element model is presented for the analysis of surface roughening of aluminum sheet metal. A hybrid finite-element model is developed which accounts for the elasto-viscoplastic constitutive response of a single crystallographic orientation. Initialization of a finite-element mesh representing several grains is performed using data gathered through automated collection of backscattered Kikuchi diffraction data. To handle a region that contains sufficient variation (contains numerous distinct grains), the implementation is carried out using distributed computation strategies. Application is made to 6111-T4 sheet metal intended for auto body applications. The numerical simulations are complemented with mechanical testing in plane strain and biaxial stretch. Based on the simulation results, there are two conclusions that can be drawn concerning the action of surface grains deforming through crystallographic slip. One is that grains can act collectively to form localized regions of thinning. The other is that grain interactions can lead to behavior which is different from that expected if grains deform with the average (macroscale) strain. Neighbor interactions can after the deformation from that computed using the macroscale deformation rate.     

Microstructural investigation of intermediate phase formation in uranium-aluminum diffusion couples

The irregular growth of the intermediate phase layer which forms as a result of interdiffusion between U and Al has been studied. Using optical and scanning electron microscope examination techniques and electron-probe microanalysis, it has been determined that only one phase (UAl₃) grows in the U-Al system and that the breakdown of interfacial planarity is a result of a limited nucleation rate and rapid growth rate of UA1₃. This phase partially decomposes near the uranium end of the diffusion couple during slow cooling, resulting in the formation of a “multiphase≓ region. No such region is observed in rapidly cooled specimens. X-ray diffraction indicates the absence of a preferential growth direction to the intermediate phase layer. A model is presented that describes the sequence of intermediate phase growth.     

一种板材小圆角胀压复合成形工艺解析

针对薄壁板材零件小圆角特征成形制造难的问题,提出了一种新型胀压复合成形工艺.其关键工艺参数为:预成形高度、预成形凹圆角大小和终成形胀形压力与背压凸模运行速度匹配关系.预成形高度决定了终成形小圆角的材料储备,预成形凹圆角的最佳值为充液拉深时凸模圆角可取的最小值,通过理论分析给出了预成形高度和预成形凹圆角的计算方法.建立了胀压复合成形过程力学模型,通过应力状态分析给出了不同胀形压力与背压凸模运行速度匹配关系下坯料圆角区变形状况.同时基于有限元模拟和工艺试验,研究了预成形高度和终成形胀形压力与背压匹配路径对试验件成形质量的影响,验证了理论分析的准确性,并证明了该新工艺的适用性.