温度对不锈钢/铝/不锈钢层状材料轧制复合行为的影响

研究了热轧复合不锈钢／铝／不锈钢层状材料的粘结行为，采用剥离试验、OM、SEM及EDAX等研究了坯料加热温度对界面粘结强度及特征的影响规律。结果表明：在523～773K范围内，粘结强度随着温度的升高而明显增加；温度低于523K时，铝／钢界面为机械结合状态，粘结强度低于7．8Nmm^-1，剥离断口位于其初始界面；温度高于673K后，界面达到近冶金结合状态，粘结强度超过20．3Nmm^-1,剥离断口几乎位于铝基体而非初始界面。钢层变形远小于铝层变形，界面两侧金属剪切流动导致的新表面接触及扩散行为是促使界面粘结的主要机制。     

热压复合制备钛/铝层状复合材料界面组织演变研究

鉴于钛/铝层状复合材料在航空航天、防护装甲等领域的重要应用价值,采用热压复合法制备不同单层厚度的钛/铝层状复合材料,利用SEM、EDS对界面组织形貌以及元素分布进行表征,并结合XRD对界面物相进行分析。试验结果表明,单层厚度越小的层状复合材料扩散层厚度增加越快;单层厚度为50μm的箔材更容易形成金属间化合物;当铝箔有剩余时,只有一种物相TiAl3;当铝完全消耗时,从钛侧开始依次产生Ti_3Al、TiAl、TiAl_2、TiAl_3。     

界面涂层对厚规格热轧钢/铝复合板界面结构与力学性能的影响

针对厚规格钢/铝复合板坯料厚度大、组元差异显著、难以直接轧制复合等特点,采用等离子涂覆技术与热轧复合工艺相结合成功制备了厚规格钢/铝复合板,通过结合界面剪切强度测试和SEM、EDS等检测方法,分别探究了轧制道次、温度与压下率对界面结构与力学性能的影响规律。结果表明,与直接轧制复合相比,经表面喷涂处理后的界面结合强度明显提高,且拉剪断裂面均位于钢与涂层界面。在单道次轧制条件下,随着轧制压下率增加,钢/涂层的微观界面得到改善,界面结合强度逐渐提高。在400～500℃范围内,钢/铝界面扩散层厚度随轧制温度提高呈增加趋势、界面结合强度先增大后减小。由于变形的不协调性,增加轧制道次会破坏前一道次界面复合结果,导致结合强度剧烈下降。当轧制温度为450℃、单道次压下率为40%时,钢/铝复合板界面剪切强度达66 MPa,符合相关标准要求。研究成果为厚规格钢/铝复合板生产制备提供了一种新途径。     

SiC_p/2024Al复合材料高应变率热变形行为的新本构模型

通过分离式霍普金森压杆(SHPB)动态压缩试验研究了体积分数为45%的铝基碳化硅颗粒增强复合材料(SiC_p/2024Al)在大应变率和变形温度范围内的热变形行为,分析了热变形参数(变形温度和应变率)对流动应力的影响。研究发现:变形温度和应变率对复合材料的流变应力、抗压强度、弹性模量、应变率敏感性有显著影响;抗压强度、弹性模量随变形温度的增大而减小,而抗压强度、弹性模量、应变率敏感性随应变率的增大出现了拐点。根据试验结果,结合热力学和统计损伤力学理论,建立了描述SiC_p/2024Al复合材料动态热变形行为的连续损伤本构模型,预测的流动应力与试验结果吻合较好,表明所建立的模型能够准确地描述SiC_p/2024Al复合材料动态热变形行为。     

SiCp/2024Al复合材料高应变率热变形行为的新本构模型#br#

通过分离式霍普金森压杆(SHPB)动态压缩试验研究了体积分数为45%的铝基碳化硅颗粒增强复合材料（SiCp/2024Al）在大应变率和变形温度范围内的热变形行为,分析了热变形参数（变形温度和应变率）对流动应力的影响。研究发现：变形温度和应变率对复合材料的流变应力、抗压强度、弹性模量、应变率敏感性有显著影响;抗压强度、弹性模量随变形温度的增大而减小,而抗压强度、弹性模量、应变率敏感性随应变率的增大出现了拐点。根据试验结果,结合热力学和统计损伤力学理论,建立了描述SiCp/2024Al复合材料动态热变形行为的连续损伤本构模型,预测的流动应力与试验结果吻合较好,表明所建立的模型能够准确地描述SiCp/2024Al复合材料动态热变形行为。     

切削参数对SiCp/Al复合材料切削变形的影响

为研究切削参数对SiC_p/Al复合材料切削变形的影响,通过试验测量的切削力和切屑厚度,计算得到SiC_p/Al复合材料的变形区参数,并分析了切削参数对变形区参数的影响规律,同时拟合得到了切削SiC_p/Al复合材料过程中剪切角与摩擦角的关系。研究结果表明:进给量增大,SiC_p/Al复合材料变形系数和剪应变减小,摩擦角减小,剪切角增大,且SiC_p/Al复合材料的摩擦角大于2024Al,剪切角小于2024Al;切削速度增大,SiC_p/Al复合材料变形系数、剪应变都减小,摩擦角减小但是不显著,剪切角增大; SiC_p/Al复合材料φ=B-C(β-γ)中B值大于2024Al,而斜率C(负值)小于2024Al。     

铝/铜拉拔复合工艺的研究

为了提高Al/Cu复合材料的性能及使用价值,研究了在不同的拉拔工艺参数条件下Al/Cu的复合成形,获得了有利于这2种金属成形的工艺参数.通过对拉拔复合后的Al/Cu双金属棒的扩散退火试验,探讨了热处理规范对双金属复合界面的影响规律.结果表明,拉拔的变形程度对Al/Cu界面复合效果起重要作用,随着变形程度的增加Al/Cu界面复合的效果得到明显改善.拉拔变形程度大于28%的Al/Cu棒复合较好;对于Al/Cu拉拔复合棒可以采用的热处理规范为:温度400 ℃,保温时间2 h.     

不同形貌Al-Fe金属的块体压制成形模拟研究

文章以含40%Al的Al-Fe复合金属为研究对象,对颗粒状和屑状40Al-Fe复合金属分别进行压制预变形,并对屑状40Al-Fe复合金属预制坯进行了二次热压缩变形,重点研究压制预变形及二次热压缩对Al-Fe复合金属成形性和界面影响。结果表明：压力为16 MPa时,颗粒状40Al-Fe复合金属预制坯(密度为4.54 g/cm³)成形性良好且形成致密界面;压力为16 MPa时,屑状40Al-Fe复合金属预制坯(密度为3.50 g/cm³)可以成形但界面存在孔洞,Al屑主要为“片层状”“狗牙状”“圆圈状”“波浪状”,其经二次热压缩变形,“圆圈状”Al屑连成一个整体,“狗牙状”与“波浪状”Al屑均演变为“片层状”,而Fe屑仍为“片层状”“块状”,未发生明显变形。变形温度300℃、变形速率0.5 s^-1、变形程度0.1是目前生产工艺最佳参数,此时屑状40Al-Fe复合金属成形性最佳且界面结合良好(密度为4.66 g/cm³)。     

轴承套圈坯料螺旋孔型斜轧成形数值模拟及分析

针对传统解析计算和物理试验不能有效揭示轴承套圈坯料螺旋孔型斜轧工艺轧制变形机理的问题,基于Abaqus/CAE有限元分析软件建立轴承套圈坯料螺旋孔型斜轧成形三维有限元模型,其关键点为设置轧辊与轧件网格表面为面接触以及网格内部表面为自接触,采用高温单向拉伸试验确定韧性断裂模型中坯料的损伤参数,添加STATUS变量输出控制网格畸变等,并分析了轧制过程中坯料的应变和应力以及轧辊的轧制力和力矩,结果表明坯料内部区域处于多向拉应力状态,易导致内部微缺陷的萌生和扩展。     

Mg/Al复合板波纹轧模拟及变形区微观组织演变分析

通过建立Mg/Al复合板波纹轧热力耦合有限元模型并进行轧卡实验,分析了应力、应变及温度对金属变形以及微观组织演变的影响。结果表明,当波纹轧初始轧制温度为400 ℃、平均压下率为35%时,复合板在变形区靠近出口位置实现复合,复合界面波谷处扩散层厚度为3.3 μm,波峰处扩散层为2.7 μm;等效应变和温度的增加促进了镁合金的变形晶粒发生动态再结晶,其微观组织主要包括等轴晶、孪晶以及动态再结晶晶粒,界面波谷处晶粒平均尺寸为3.71 μm,波峰处为6.92 μm。     

冲压用热轧钢板的冷变形特性

在二辊轧机上对CSP轧制的SPHD钢板进行了冷变形,在拉伸试验机上测定了冷变形后钢板的抗拉强度和伸长率,分析了其加工硬化的情况,并对不同冷变形程度下钢板轧制方向的横截面组织进行了分析.结果表明:经冷变形后,试验钢的抗拉强度σb增大,伸长率δ减小,抗拉强度变化量△σb随着变形量的增大而增大,加工硬化明显;轧向横截面晶粒随着变形量的增大而细化.     

Analytical and experimental study on bonding behavior at the roll gap during complex rolling of sandwich sheets

An extended analytical model for complex rolling of sandwich sheets is proposed. Effects of various rolling conditions such as the flow stress ratio and initial thickness ratio of the raw sheets, total thickness reduction, etc., upon the bonding factors such as the bonding length, mean contact pressure, and the relative sliding distance at the interface as well as the newly generated surface ratio are analyzed. Furthermore, experiments on complex rolling of sandwich sheets are also conducted. The measured rolling force, thickness ratio of the rolled product, bonding length, and the mean contact pressure are close to the theoretical values. Through the comparisons, the validity of this proposed mathematical model is verified and the characteristics of the bonding behavior at the roll gap during complex rolling of sandwich sheets are manifested.     

超高强度钢热场-超声复合滚压表层微观组织强化机制

针对超高强度钢冷塑性变形能力弱、表面形变强化难度大的问题,提出热场-超声复合滚压强化方法。开展45CrNiMoVA钢表面热场-超声复合滚压试验,利用SEM、EBSD和TEM等检测手段,结合表面层残余应力分布结果,表征、分析表层微观组织的演变与强化机制。发现在声软化效应和热软化效应耦合作用下,热场-超声复合滚压后45CrNiMoVA钢表层材料的塑性变形程度加剧,塑性变形层深度增加,表层材料发生晶粒细化,形成沿深度方向晶粒尺寸呈梯度分布的微观组织结构,细晶强化和位错强化是主要的强化机制。证明了热场-超声复合滚压方法的有效性,对超高强度钢零件表面强化处理技术的发展具有重要意义。     

Evaluation of Occurrence of Surface Brightness Irregularity in Cold Rolling of Stainless Steel with Emulsion

The manufacturing of stainless steel with higher brightness is improved using emulsion oil. However, in cold rolling of stainless steel with emulsion oil, it is well known that the surface brightness irregularity on the sheet surface after rolling occurs when the rolling speed is higher. It is estimated from the experimental results that the cause of the surface brightness irregularity is due to the degree of starvation in the emulsion rolling. The rolling experiments of the stainless steel with oil-in-water emulsion were carried out at various rolling speeds. The inlet oil film thickness was estimated using the evaluating system. In cold sheet rolling of stainless steel with emulsion oil, the surface brightness irregularity occurred at a rolling speed of 0.6 m/s with emulsion concentrations of 3, 5, and 10%. The experimental results showed that the surface brightness irregularity at cold coil rolling with emulsion of stainless steel occurred under a degree of starvation value of 0.16.     

Molecular dynamics simulation of tensile behavior of diffusion bonded Ni/Al nanowires

Interfaces play key roles in determining mechanical properties of materials. In current work we perform molecular dynamics simulations of diffusion bonding to evaluate the effect of temperature on the morphology of the Ni/Al interface and the strength of the diffusion bonded Ni/Al nanowires. The centro-symmetry parameter is adopted to identify defect atoms generated. Simulation results show that the thickness of the Ni/Al interface has strong dependence on the temperature of diffusion bonding. Following uniaxial tension tests indicate that the yield strength of Ni/Al nanowires is smaller than both the single crystalline Ni and Al nanowires, because of the Ni/Al interface acting as dislocation source and the mobilization of pre-existing dislocations at high temperature. It is shown that the mechanical properties of diffusion bonded Ni/Al nanowires strongly depend on the temperature.     

Influence of the filler materials on flux-free brazing of pure aluminium (1050)

In the present study, samples of pure aluminium (1050) were deposited by cold spraying with filler materials such as Al12Si, Al7Si, Al12Si-4%Cu, and the Al-Si-based filler material A, which was especially developed for flux-free brazing by the Surface Engineering Institute. Besides, pure Si powder was also sprayed. The coated samples were heat-treated under different conditions and were brazed under an argon atmosphere without fluxes or with the flux Nokolok by an induction heating system. The shear strength of the brazed joints was determined. The results show that the filler materials could be well deposited by cold spraying. A thin layer of brittle Si could also form due to the strong deformation of the substrate surface. The heat treatments showed that a very good metallurgical bond between the filler materials and the substrate could be realized by the deposition by cold spraying. The Al7Si deposited samples could not be brazed without fluxes under the given conditions. The samples deposited with other filler materials could be brazed without fluxes. The in-situ diffusion process made it possible to braze the Si-deposited samples at 580°C. The joints of the samples deposited with the filler material A showed the highest shear strength of 41 MPa, whereas the values of the Al12Si and Si deposited samples were less than 20 MPa. The employment of the flux Nikolok significantly increased the shear strength of the Al12Si deposited samples to more than 53 MPa.     

复合陶瓷挺柱钎焊变形的研究及其控制

复合陶瓷挺柱钎焊后,由于陶瓷、金属线膨胀系数的不同,在挺柱中产生较大的残余应力和变形,从而影响其使用性能,通过试验,研究了影响挺柱变形的因素和规律。结果表明,钢套的强度和厚度、钎料的厚度、熔点及强度是影响挺柱焊后变形的主要因素,采用高屈服极限或者较厚的钢套时钎焊变形较小;钎料厚度较厚时钎焊变形较大,采用低熔点,低屈服极限的Sn基活性钎料可显著地降低钎焊变形,基本可能满足挺柱工作的表面凸起量要求。     

铝材冷轧变形区油膜形成机理及影响因素

通过计算分析与轧制实验，探讨了名材冷轧变形区油膜形成机理及影响因素结果表明：流劝动力学成膜机理主要依赖于润滑剂粘度和轧制速度，特别是润滑剂粘度较氏时，轧制速度必须达到一定值，否则无法形成有效的油膜，而机械夹带作为低粘，低速条件下变形区主要成膜机理，其膜厚度依赖于轧辊与轧件粗糙度和夹带系数ｍ，０．１〈ｍ〈０．５，且随润滑剂粘度提高而增大。     

Application of cold spraying for flux-free brazing of aluminium alloy 6060

In the present study, samples of aluminium alloy 6060 were coated by cold spraying with a powder of brazing alloy Al12Si. The influence of the process gas temperature on particle velocities and coating build-up was investigated. The coated samples were heat-treated in air and under argon atmosphere to investigate the wetting behaviour of the deposited Al12Si and the diffusion processes between Al12Si coatings and substrates. Coated samples were brazed flux-free under argon atmosphere by an induction heating system. The microstructure of the coated, heat-treated, and brazed samples was investigated. The shear strength of the brazed joints was determined. The results show that the brazing alloy Al12Si could be very well deposited on the substrate by cold spraying. The particle velocity increased with increasing process temperature. Correspondingly, the thickness of Al12Si coatings increased with increasing process temperature. The heat treatments showed that a very good metallurgical bond between the Al12Si coatings and the substrate could be realized by the deposition using cold spraying. The coated samples could be well brazed without fluxes. The coating thickness and overlap width influenced the shear strength of the brazed joints. The highest shear strength of brazed joints amounts to 80 MPa.