锌基镀层热成形钢裂纹的产生、扩展机理及高温力学性能研究

本文通过锌基镀层热成形钢的Gleeble试验和实际零件热冲压试验,在材料高温性能分析的基础上,建立了材料模型,用于高精度地拟合真应力和真应变之间的关系,进而研究成形温度、铁素体形成和弯曲变形对液态锌致基板脆裂(LMIE)的影响。结果表明,真应力随着变形温度的下降而增加。当变形温度为820℃时,LMIE导致真应变较低,约为0.13。根据Gleeble热模拟测试和实际零件试验结果,建议成形温度为720℃,可以避免LMIE并保证材料的力学性能。在实际应用中,拉应力容易导致微裂纹的产生,而压应力可以抑制微裂纹的产生。随着成形温度的降低,镀层中微裂纹的数量和宽度降低,同时镀层厚度增加。镀层主要为固态α-Fe(Zn)相。通过减少在加热保温和成形过程中的液态相可以减少甚至避免LMIE裂纹的产生。

Forming defects in aluminum alloy hot stamping of side-door impact beam

The forming defects, including thinning, rupture, wrinkling and springback, usually arising in producing a side-door impact beam, were investigated by trial and numerical simulation. A temperature-related constitutive model specific to the temperature range from 350 °C to 500 °C was established and used for the numerical simulation. The trial and numerical simulation were conducted to clarify the quantitative characteristics of forming defects and to analyze the effects of process parameters on the forming defects. Results show that the rupture situation is ameliorated and the springback is eliminated in the aluminum alloy hot stamping. The wrinkling severity decreases with increasing blank holder force (BHF), but the BHF greater than 15 kN causes the rupture at the deepest drawing position of workpiece. The forming defects are avoided with lubricant in the feasible ranges of process parameters: the BHF of 3 to 5 kN and the stamping speed of 50 to 200 mm/s.

铝合金热冲压板件多目标优化

为解决铝合金热冲压板件存在的减薄和回弹等缺陷,采用响应面法分析了板料初始成形温度和压边力对最大减薄率和最大回弹量的影响规律。结果表明：成形件的最大减薄率随着板料初始成形温度和压边力的增大而增加;最大回弹量随着板料初始成形温度和压边力的增大而下降。最大减薄率和最大回弹量之间具有一定的冲突性。为解决这种冲突,采用多目标遗传算法NSGA-II进行多目标优化,得到Pareto最优解。进而在保证最大减薄率和最大回弹量都相对较小的情况下,确定合理的铝合金热冲压板件的工艺参数范围：板料初始成形温度为470.86~520°C;压边力为110~131.78k N。试验结果表明,合理的工艺参数可以避免破裂和减少回弹。仿真结果与试验具有较好的一致性。

AA6082铝合金热变形损伤本构模型

利用Gleeble-1500热力模拟试验机在温度为425~525℃、应变速率为0.01~1 s-1条件下对AA6082铝合金进行热拉伸试验,研究该合金的热变形行为。结果表明:变形温度、应变速率和应变对AA6082铝合金的流变应力影响显著,流变应力随变形温度的升高而下降,随应变速率的提高而增加;材料热变形经历了应变硬化段、稳态变形段和由损伤引起的流变应力陡降段。建立AA6082铝合金热变形统一黏塑性损伤本构模型,该模型综合考虑位错、硬化、损伤、应变、应变速率和温度等因素,借助遗传算法工具箱确定模型中材料常数。该模型能够较好地预测AA6082铝合金热变形时的流变应力,同时可以较好地描述材料的损伤演化行为。

Effect of friction coefficient in deep drawing of AA6111 sheet at elevated temperatures

The effect of friction coefficient on the deep drawing of aluminum alloy AA6111 at elevated temperatures was analyzed based on the three conditions using the finite element analysis and the experimental approach.Results indicate that the friction coefficient and lubrication position significantly influence the minimum thickness,the thickness deviation and the failure mode of the formed parts.During the hot forming process,the failure modes are draw mode,stretch mode and equi-biaxial stretch mode induced by different lubrication conditions.In terms of formability,the optimal value of friction coefficient determined in this work is 0.15.At the same time,the good agreement is performed between the experimental and simulated results.Fracture often occurs at the center of cup bottom or near the cup corner in a ductile mode or ductile-brittle mixed mode,respectively.

6111铝合金固溶工艺多目标优化

利用电子拉伸试验机和维氏硬度计测试不同固溶处理后6111铝合金板的抗拉强度、伸长率和维氏硬度,以固溶温度和固溶时间为自变量,采用响应面模型对抗拉强度、伸长率和维氏硬度进行拟合,并对其进行单目标优化。结果表明:固溶处理工艺参数分别为(540.8℃,31.8 min)、(496.6℃,1.0 min)、(540.6℃,32.0 min)时,抗拉强度、伸长率和维氏硬度达到最大,分别为299.12 MPa、24.95%和106.62;应用第二代非支配排序遗传算法,对多个响应面模型进行优化求解,得到多目标优化模型的Pareto解集,从中可选择使铝合金板综合力性能较好的解,进而获得对应的固溶工艺参数。

铝合金热冲压过程数值模拟分析

铝合金热冲压工艺可用于一次性成形形状复杂的零件。本文以热冲压某铝合金大尺寸板件为例,利用数值模拟软件研究了热冲压过程中的应力、应变和厚度分布变化情况。冲压过程中,极限应力应变值由凸模圆角处转移到零件侧壁区。冲压成形后,厚度最小值也在侧壁区附件,与应力应变分布具有较高的一致性。从而对铝合金热冲压工艺有更深入的了解,为该工艺的研究和应用提供一定的理论参考。

Influence of process parameters on deep drawing of AA6111 aluminum alloy at elevated temperatures

To gain a deep insight into the hot drawing process of aluminum alloy sheet, simulations of cylindrical cup drawing at elevated temperatures were carried out with experimental validation. The influence of four important process parameters, namely,punch velocity, blank holder force(BHF), friction coefficient and initial forming temperature of blank on drawing characteristics(i.e.minimum thickness and thickness deviation) was investigated with the help of design of experiments(DOE), analysis of variance(ANOVA) and analysis of mean(ANOM). Based on the results of ANOVA, it is shown that the blank holder force has the greatest influence on minimum thickness. The importance of punch velocity for thickness deviation is 44.35% followed by BHF of 24.88%,friction coefficient of 15.77% and initial forming temperature of blank of 14.995%. After determining the significance of each factor on forming characteristics, how the individual parameter affects characteristics was further analyzed by ANOM.

Influence of process parameters on properties of AA6082 in hot forming process

The influences of process parameters on mechanical properties of AA6082in the hot forming and cold-die quenching(HFQ)process were analysed experimentally.Transmission electron microscopy was used to observe the precipitate distribution and to thus clarify strengthening mechanism.A new model was established to describe the strengthening of AA6082by HFQ process in this novel forming technique.The material constants in the model were determined using a genetic algorithm tool.This strengthening model for AA6082can precisely describe the relationship between the strengths of formed workpieces and process parameters.The predicted results agree well with the experimental ones.The Pearson correlation coefficient,average absolute relative error,and root-mean-square error between the calculated and experimental hardness values are0.99402,2.0054%,and2.045,respectively.The model is further developed into an FE code ABAQUS via VUMAT to predict the mechanical property variation of a hot-stamped cup in various ageing conditions.

液压伺服系统设计与分析

介绍了采用液压伺服系统替代某一电机伺服系统的过程。主要设计了液压伺服系统回路，同时对系统回路的整体功能、各液压元件的功能和选型等相关细节进行了介绍。通过建立液压伺服系统仿真模型，确定了系统的稳定性，并进一步证明了通过增加超前校正网络、减小开环增益和增加马达排量等均可进一步增进系统的稳定性。分析结果表明，通过设计合理的液压伺服系统，可以实现对电机伺服系统的替代。

Influence of process parameters and defect analysis in hot deep drawing process of aluminum alloy AA6082

In this study, a novel punch toolset was developed to investigate the hot stamping of AA6082-T4 sheet. The effect of the process parameters, including forming temperature, punching velocity, friction coefficient, and blank holder force(BHF) on formability was quantified using Taguchi design, analysis of variance(ANOVA) and mathematical statistics. The finite element(FE) model has been established in software Pamstamp for simulation and analysis of their effects on the minimum thickness and thickness variation of the hot-stamped component. The major factors influencing the minimum thickness of the hot-stamped part has been found to be BHF and friction coefficient with influence significance of 35.3% and 34.88%, respectively. Additionally, punch velocity and BHF affect the thickness deviation significantly with influence significance of 40.43% and 35.42%, respectively. Furthermore, a serious thinning occurs on the punch corner region of the hot-stamped cup when the BHF is larger than 2.4 kN. The thickness deviation of the hotformed cup has been found to be firstly decreased and then increased with the increase of punch velocity. Low friction coefficient between punch and blank led to crack at bottom centre of the cup. Moreover, different type, phenomenon and mechanism of defects occurring during hot stamping process, such as crack and wrinkling, were discussed. The crack mode was dimple-dominated ductile fracture, which was induced by micro-void nucleation, growth and coalescence.

T形连接模型的冲击特性研究

T形接头的连接端头主要有连续法兰和开口法兰两种形式。为了揭示法兰形式对T形接头冲击特性的影响,采用LSDYNA对不同法兰边的薄壁梁T形接头进行仿真计算,在正向和侧向两种冲击状态下,研究不同形式接头的变形形式、位移和能量随时间的变化,同时分析了接头的刚度和开口法兰轻量化后的冲击特性,分析结果表明:在正向冲击下,不同接头的位移与能量随时间的变化基本相同,正向冲击的速度对变形结果影响很小;但是在侧向冲击下,法兰边出现开口后接头的变形形式发生改变,由下部折弯转变为缺口处褶皱,接头的位移量增大,冲击性能降低。接头的刚度随着法兰边的减少而逐渐减小。在接头服役条件中主要承受正向冲击时,可以使用开口法兰替换连续法兰,并可以进行高强材料替换实现轻量化。

耦合位错密度的6111铝合金热变形本构模型

利用Gleeble-1500热模拟试验机对6111铝合金进行高温拉伸试验,研究了其在变形温度为350、450和550℃以及应变速率为0.1、1和10 s 1时的热变形行为.6111铝合金的流变应力随温度升高而减小,随应变速率增大而增大,其热变形从应变硬化阶段过渡到稳态变形阶段.建立了综合考虑应变、温度和应变速率对流变应力的影响以及耦合位错密度的统一黏塑性本构模型,并通过遗传优化算法求解出本构模型中的材料常数.模型计算得到的真应力-真应变曲线与试验数据吻合较好.

热冲压工艺参数对零件成形性影响规律分析

主要研究了热冲压工艺参数对热冲压后零件成形性的影响规律。热冲压工艺参数主要包括冲压速度、压边力、摩擦因数和板料温度,每个工艺参数均分为低、中、高3个水平。结合测试方案设计和仿真模型,利用方差分析研究不同工艺参数对零件成形性的影响程度;同时,利用量化分析方法确定不同水平的工艺参数对零件成形性影响程度的量化值。结果表明,工艺参数对零件减薄率的影响程度由重到轻的顺序为摩擦因数、板料温度、冲压速度和压边力,其中摩擦因数影响程度的量化值约为97.3%。

热处理工艺对铝硅镀层热成形钢组织性能的影响

为深入理解不同热处理工艺参数对铝硅镀层热成形钢组织性能的影响规律,主要研究了加热温度和保温时间对铝硅镀层热成形钢的硬度、微观组织、镀层厚度和镀层成分的影响。结果表明,当加热温度不大于900℃时,铝硅镀层热成形钢的硬度随着保温时间的增加而增加;当加热温度大于900℃时,铝硅镀层热成形钢的硬度随着保温时间的增加而下降。当加热温度为850~930℃,保温时间为4、8 min时铝硅镀层热成形钢的微观组织在模具淬火冷却过程中均转化成为马氏体。在相同加热温度下,铝硅镀层热成形钢合金层的厚度随着保温时间的增加而增大,当加热温度升高至930℃时,镀层因氧化而挥发严重,导致镀层变薄,所以铝硅镀层热成形钢的加热温度应控制在930℃以下。保温温度升高、保温时间增加导致元素扩散显著,聚集的硅元素含量和面积由于其不断向四周扩散而降低。同时铁元素大量扩散到镀层中,镀层中铁元素含量增加显著。高温下,镀层发生明显的氧化反应,氧化反应促进了微孔洞的形核和长大。

液压伺服系统设计与分析

文章介绍了采用液压伺服系统替代某一电机伺服系统的过程。主要设计了液压伺服系统回路,对系统回路的整体功能、各液压元件的功能和选型等相关细节进行阐述。通过建立液压伺服系统仿真模型,确定了系统的稳定性,并进一步证明了通过增加超前校正网络、减小开环增益和增加马达排量等均可进一步增进系统的稳定性。分析结果表明,通过设计合理的液压伺服系统,可以实现对电机伺服系统的替代。

预拉伸对不同强度汽车用高强钢弯曲回弹的影响

通过试验对汽车用高强钢的弯曲回弹特性进行了研究,主要分析了预拉伸对材料回弹的影响。针对HC330/590DH,HC340/590DP和HC420/780DP3种高强钢进行了不同程度的预拉伸,预拉伸后进行三点折弯,并进行了回弹量的测量。对材料的应变、减薄和回弹以及微观组织等进行了分析。研究表明:对于同一材料不同预拉伸量时,回弹量随着预拉伸量的增大而增大;对于同一类型不同强度的高强钢,随着材料强度的增加,回弹量增加;HC340/590DP材料的微观组织在弯曲变形后,内层区晶粒压缩,外层区晶粒拉伸变长,对于同强度不同微观组织的两种材料,传统双相钢(DP钢)的回弹量大于成形增强型双相钢(DH钢)的回弹量。