C5191磷青铜的动态拉伸性能和变形机制（英文）

为了探讨C5191磷青铜在高应变速率条件下的动态响应,解决高速冲压工艺问题,利用电子万能材料试验机和分离式Hopkinson拉杆装置对C5191磷青铜分别进行应变速率为0.001和500、1000、1500 s~(-1)的准静态和动态拉伸试验,结合SEM和TEM等手段,研究了C5191磷青铜的动态拉伸性能及其变形机制。结果表明:C5191磷青铜高应变速率动态拉伸与准静态条件相比较,其屈服强度和抗拉强度分别提升了32.77%和11.07%;应变硬化指数由0.075增加到0.251;材料强度的应变速率敏感指数由0.005变化到0.022,呈现出明显的应变速率敏感性;高应变速率动态拉伸过程中,位错运动速度加快,导致位错"近程阻力"加大,使C5191磷青铜的变形抗力随着应变速率的增加而增大。可动位错数量的显著增多,多系滑移的开启,以及绝热温升软化效应在一定程度上提高了C5191磷青铜高应变速率动态拉伸时的塑性。     

汽车用6005A-T6铝合金动态性能研究

通过对6005A-T6铝合金进行准静态拉伸试验和动态拉伸试验,研究了应变速率对6005A-T6铝合金准静态和动态力学性能及断裂行为的影响。6005A-T6铝合金的强度随着应变速率提高而增大,应变速率200/s拉伸的抗拉强度、屈服强度分别较准静态拉伸提升30MPa、25MPa,其中以准静态到应变速率10/s的过程中,材料的抗拉强度、屈服强度上升最为明显;6005A-T6铝合金塑性随着应变速率的增大而逐渐增大,当应变速率达到200/s时塑性反而下降。在高速拉伸变形状态下,位错密度的增加和滑移带的增多是导致高速状态下强度及延伸率提高的主要原因;当应变速率达到200/s时由于拉伸速率过快,晶粒来不及进行大量变形是断后延伸率反而降低的主要原因。     

基于修正Johnson-Cook模型的C5191-H磷青铜高速冲裁本构关系

针对高速冲裁过程中材料的应变硬化、应变速率强化、热软化效应数据难以获取,无法建立物理仿真动态模型的问题,利用Gleeble-3500热模拟试验机和分离式Hopkinson拉杆装置对C5191-H磷青铜分别进行应变速率为1、500、1000和1500 s-1、温度为20～400℃的拉伸试验,利用试验数据拟合并修正了经典的Johnson-Cook动态方程,并在高速冲裁数值模拟中验证了修正后的本构方程的有效性。结果表明:C5191-H磷青铜拉伸变形时呈现出明显的应变硬化和应变速率敏感性;利用试验数据拟合并修正应变强化项的Johnson-Cook动态本构模型,此模型具有较高的大应变、高速率、热效应本构关系描述精度,并能较好地描述该材料的高速冲裁物理仿真过程。     

汽车用6005A-T6铝合金动态力学性能研究

通过对6005A-T6铝合金进行准静态拉伸试验和动态拉伸试验,研究了应变速率对6005A-T6铝合金准静态和动态力学性能及断裂行为的影响。结果表明:6005A-T6铝合金的强度随着应变速率提高而增大,当拉伸应变速率达到200s-1时,抗拉强度、屈服强度分别较准静态拉伸提高30MPa、25MPa,其中以准静态到应变速率10 s-1的过程中,材料的抗拉强度、屈服强度上升最为明显;试样应变速率与流变应力的关系符合Johnson-Cook本构模型,其拟合得到的本构方程为σ=(220.56+298.85ε~(0.506))(1+0.0209ln■)。6005A-T6铝合金塑性随着应变速率的增大而逐渐增大,当应变速率达到200s-1时塑性反而下降。在高速拉伸变形状态下,位错密度的增加和滑移带的增多是导致高速状态下强度及延伸率提高的主要原因;当应变速率达到200s-1时由于拉伸速率过快,晶粒来不及进行大量变形是断后延伸率反而降低的主要原因。     

DP1180双相钢在高应变速率变形条件下应变硬化行为及机制

利用电子万能试验机和分离式Hopkinson拉杆装置对DP1180冷轧双相钢分别进行应变速率为0.001 s^-1和500,1750 s^-1的准静态和动态拉伸实验,根据修正的Swift真应力-应变模型对实验数据进行了非线性拟合,并用修正的Crussard-Jaoul分析法计算出修正的Swift模型的应变硬化指数.结果表明:在准静态和动态拉伸下,都存在两阶段应变硬化特性,第一阶段随应变速率的增加应变硬化能力增强;第二阶段随应变速率的增加应变硬化能力减弱;转折应变随应变速率的增加从3.12%减小到1.28%.在高应变速率下,马氏体附近的铁索体由于受到变形协调性的限制,形成位错结构胞块,其尺寸可达约90 nm,而且几何必需边界（GNB）的存在使得DP1180双相钢在高应变速率下变形过程中不至于瞬间破坏;在应变速率为1750 s^-1时,绝热温升△T=103℃使得马氏体更容易发生塑性变形.     

不同应变速率下DP钢变形行为的微观机理研究

利用3 000 kN电子万能试验机和ZWICK HTM5020高速拉伸试验装置研究了双相钢(DP钢)在不同应变速率(10-4~600 s-1)下的拉伸变形行为,并结合XRD分析对双相钢组织中的位错密度进行了计算。结果表明,在准静态拉伸过程中,双相钢组织中的位错密度基本不变,其抗拉强度、断裂延伸率随应变速率变化也不明显;而在动态拉伸条件下,随着应变速率的增加,双相钢组织中的位错密度不断增加,抗拉强度也相应增加,塑性降低,最终导致能量吸收下降。     

双辊铸轧和热轧处理AZ31B镁合金的动态拉伸性能（英文）

研究双辊铸轧和热轧处理AZ31B镁合金板材在室温和应变速率从0.001 s~(-1)到375 s~(-1)条件下的动态拉伸力学行为,以及力学性能与显微结构之间的关系。实验发现,该镁合金板材具有很强的初始基面纤维织构,并且在高应变速率条件下机械孪生成为主要的变形机理。材料的屈服强度和拉伸极限强度随应变速率的提高而提高;然而,孪生诱导的软化效应导致应变强化指数随应变速率的提高而成比例地降低。在准静态拉伸条件下,断裂伸长率随应变速率的提高而明显地降低;而在动态拉伸条件下应变速率对断裂伸长率的影响却不明显。最后,应用扫描电镜对拉伸试样进行了断口形貌分析。分析结果表明,该加工状态下的AZ31B镁合金板材的拉伸断裂是一种韧性与脆性混合断裂模式。     

变形对LF2铝合金高温流变应力的影响

对LF2铝合金分别在不同应变速率(0.07～0.33 S-1)和不同变形温度(220～480℃)进行高温拉伸试验,研究其热变形流变应力的变化规律.结果表明,流变应力随变形温度的升高而降低;随应变速率的增加而升高,表现出显著的应变强化和温度软化效应;且在高温、高应变速率条件下,材料发生了动态回复和局部动态再结晶.     

DP780高强钢板材高应变率变形行为及本构模型

基于MTS准静态拉伸和分离式霍普金森杆冲击拉伸实验对DP780高强钢板材在0.001、1150、1900、2800和4200 s~(-1)应变率水平下的本构行为进行了描述,获得了其高应变率变形规律,并建立了修正的Johnson-Cook(JC)动态本构模型。结果表明,动态冲击拉伸时,DP780板材的变形行为与准静态时显著不同,呈现显著的应变率强化特征。动态拉伸条件下的屈服强度和抗拉强度都要明显高于准静态条件下,屈服和抗拉强度在动态条件下随应变率升高也会有所增加,但由于绝热升温效应,应变率达到2800 s~(-1)左右时不再出现增加的趋势。基于动态拉伸数据建立的修正的JC本构模型能很好地描述和预测实验结果。     

应变速率对X70管线钢动态力学行为的影响

利用低速和高速拉伸试验机分别对X70管线钢进行不同应变速率下的室温拉伸试验,结合SEM、TEM下的原位拉伸和修正后的Swift模型等方法,探讨X70钢拉伸变形行为存在应变速率敏感性的机制。结果表明:在准静态应变速率(10-3~10-1s-1)范围内,试样的强度和塑性均无明显变化;在动态应变速率(100~103s-1)范围内,试样的抗拉强度随应变速率的增加而单调增大,断后伸长率则呈现先增后减的趋势,表现出明显的应变速率敏感性。当应变速率大于100 s-1时,位错运动的阻力显著增大,金属多晶体材料会开动多个滑移系来协调塑性变形;速率为600、800和103s-1的断口侧面均出现了微孔和微裂纹,表明该应变速率范围内试样非均匀塑性变形能力增强。     

C5191磷青铜薄板超高速冲裁断面的显微组织特征

为了研究C5191磷青铜在超高速冲裁条件下的变形机制,借助DOBBY-OMEGA F1超高速冲床完成0.12 mm厚的C5191磷青铜板材在3000冲次/分条件下的超高速冲裁试验,并分别利用EBSD和TEM技术对冲裁断面进行显微组织表征.结果发现,冲裁断面区域晶粒沿着冲裁方向拉长排列,局部区域形成较强的{001}<10...     

35% SiC_p/2024A1复合材料的热变形行为(英文)

采用Gleeble-1500D热模拟试验机,对35%SiCp/2024A1复合材料在温度350~500°C、应变速率0.01~10s-1的条件下进行热压缩试验,研究该复合材料的热变形行为与热加工特征,建立热变形本构方程和加工图。结果表明,35%SiCp/2024A1复合材料的流变应力随着温度的升高而降低,随着应变速率的增大而升高,说明该复合材料是正应变速率敏感材料,其热压缩变形时的流变应力可采用Zener-Hollomon参数的双曲正弦形式来描述;在本实验条件下平均热变形激活能为225.4 kJ/mol。为了证实其潜在的可加工性,对加工图中的稳定区和失稳区进行标识,并通过微观组织得到验证。综合考虑热加工图和显微组织,得到变形温度500°C、应变速率0.1~1 s-1是复合材料适宜的热变形条件。     

Effect of strain rate on deformation behavior of TRIP steels

Tensile deformation behavior of Si–Mn TRIP (TRansformation Induced Plasticity) steel with vanadium and without vanadium and the DP (Dual Phase) steel of the same composition were studied in a large range of strain rate (0.001–2000 s^?1) by routine material testing machine, rotation disk bar–bar tensile impact apparatus and high-speed material testing machine of servo-hydraulic type. In situ measurement of the transformation of retained austenite was performed by means of X-ray stress apparatus in order to have detailed knowledge about the transformation of retained austenite at quasi-static tensile. Microstructure of steels before and after tensile were observed by means of optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). It is shown that there is no yield plateau observed on the stress–strain curve at quasi-static condition for TRIP steel containing vanadium because the vanadium carbide suppress the formation of Cottrell atmosphere in matrix. Retained austenite of Si–Mn TRIP steel containing vanadium transforms to martensite at loading stress of 502 MPa (its yielding strength is 486 MPa), while the transformation of retained austenite in matrix of Si–Mn TRIP steel without vanadium happens when its yielding process is finished at quasi-static tensile. It is confirmed that phase transformation of retained austenite in TRIP steel is strain induced phase transformation. It is noted that tensile elongation of TRIP steel at dynamic tensile is always lower than that at quasi-static tensile. That is because gradually strain induced phase transformation of retained austenite in TRIP steel is suppressed by deformation localization at dynamic tensile.     

Dynamic tensile behaviors of AZ31B magnesium alloy processed by twin-roll casting and sequential hot rolling

The dynamic tensile behavior of twin-roll cast-rolled and hot-rolled AZ31B magnesium alloy was characterized over strain rates ranging from 0.001 to 375 s⁻¹ at room temperature using an elaborate dynamic tensile testing method, and the relationship between its mechanical properties and microstructures. It is observed that the sheet has a strong initial basal fiber texture and mechanical twinning becomes prevalent to accommodate the high-rate deformation. The yield strength and ultimate tensile strength monotonically increase with increasing the strain rate, while the strain hardening exponent proportionally decreases with increasing the strain rate due to twinning-induced softening. The total elongation at fracture distinctly decreases as the strain rate increases under quasi-static tension, while the effect of strain rate on the total elongation is not distinct under dynamic tension. Fractographic analysis using a scanning electron microscope reveals that the fracture is a mixed mode of ductile and brittle fracture.     

A Novel Cu-10Zn-1.5Ni-0.34Si Alloy with Excellent Mechanical Property Through Precipitation Hardening

A novel Cu-10Zn-1.5Ni-0.34Si alloy was designed to replace the expensive tin-phosphor bronze in this paper. The alloy had better comprehensive mechanical properties than traditional C5191 alloy. The aged Cu-10Zn-1.5Ni-0.34Si alloy had a hardness of 220 HV, electrical conductivity of 28.5% IACS, tensile strength of 650 MPa, yield strength of 575 MPa and elongation of 13%. Ni₂Si precipitates formed during aging, and the crystal orientation relationship between matrix and precipitates was: (001)_α//(001)_δ, and [110]_α//[100]_δ. Ductile fracture surface with deep cavities was found in the alloy. Solid solution strengthening, deformation strengthening and precipitation strengthening were found to be core strengthening mechanisms in the alloy.     

Microstructure and elevated-temperature tensile properties of differential pressure sand cast Mg-4Y-3Nd-0.5Zr alloy

The microstructures of an Mg-4Y-3Nd-0.5Zr alloy by differential pressure casting were investigated using scanning electron microscopy(SEM) and transmission electron microscopy(TEM), and its tensile deformation behavior was measured using a Gleeble1500 D themo-simulation machine in the temperature range of 200 to 400 °C at initial strain rates of 5×10-4 to 10-1 s-1. Results show that the as-cast microstructure consists of primary α-Mg phase and bone-shaped Mg5 RE eutectic phase distributed along the grain boundary. The eutectic phase is dissolved into the matrix after solution treatment and subsequently precipitates during peak aging. Tensile deformation tests show that the strain rate has little effect on stress under 300 °C. Tensile stress decreases with an increase in temperature and the higher strain rate leads to an increase in stress above 300 °C. The fracture mechanism exhibits a mixed quasi-cleavage fracture at 200 °C, while the fracture above 300 °C is a ductile fracture. The dimples are melted at 400 °C with the lowest strain rate of 10-4 s-1.     

新型Al-Mg-Zn合金不同应变率动态冲击性能与组织变化

通过Gleeble-1500、分离式Hopkinson压杆、金相、扫描和透射电镜探究了Al-Mg-Zn合金准静态及动态冲击过程中的力学性能和组织演化。Al-Mg-Zn合金在准静态下表现为整体应变硬化效应。合金在1300s_^-1~3800s_^-1对应变率敏感,在4800s_^-1时几乎无应变率敏感性。合金晶粒随应变率变化发生不同程度的变形,且随着应变率的提高,晶粒变形不均匀性加重;析出相粒子形态、密度、尺寸等在4800s_^-1动态冲击前后发生明显变化。     

Flow Stress and Processing Map of a PM 8009Al/SiC Particle Reinforced Composite During Hot Compression

Hot compression tests of 8009Al alloy reinforced with 15% SiC particles (8009Al/15%SiC_p composites) prepared by powder metallurgy (direct hot extrusion methods) were performed on Gleeble-3500 system in the temperature range of 400-550 °C and strain rate range of 0.001-1 s^?1. The processing map based on the dynamic material model was established to evaluate the flow instability regime and optimize processing parameters; the associated microstructural changes were studied by the observations of optical metallographic and scanning electron microscopy. The results showed that the flow stress increased initially and reached a plateau after peak stress value with increasing strain. The peak stress increased as the strain rate increased and deformation temperature decreased. The optimum parameters were identified to be deformation temperature range of 500-550 °C and strain rate range of 0.001-0.02 s^?1 by combining the processing map with microstructural observation.     

Tensile behavior of a free-standing Pt-aluminide (PtAl) bond coat

The tensile behavior of a high activity stand-alone Pt-aluminide (PtAl) bond coat was evaluated by the micro-tensile test method at various temperatures (room temperature to 1100 °C) and strain rates (10^?5 s^?1–10^?1 s^?1). At all strain rates, the stress–strain behavior of the stand-alone coating was significantly affected by the variation in temperature. The stress–strain response was linear, indicating brittle behavior, at temperatures below the brittle–ductile transition temperature (BDTT). The coating exhibited appreciable ductility (up to 2%) above the BDTT. The strength (both yield stress and ultimate tensile strength) of the coating decreased and its ductility increased with increasing temperature above the BDTT. The tensile behavior of the coating was sensitive to strain rate in the ductile regime, with its strength increasing with increasing strain rate at any given temperature. The BDTT of the coating was found to increase with increasing with increasing strain rate. The coating exhibited two distinct mechanisms of deformation above the BDTT. The transition temperature for the change of deformation mechanism also increased with increasing strain rate.