等轴和片层组织Ti-55511合金热轧及退火过程中的组织演变及力学性能

锻态Ti-55511合金经过不同的热处理工艺,获得等轴和片层2种初始组织。采用SEM、EBSD、TEM和拉伸试验研究了等轴和片层Ti-55511合金在热轧和退火过程中的组织演变和力学性能。结果表明：经750 ℃轧制,等轴组织中的α相轻微变形,β相发生动态回复和动态再结晶;而片层组织中的α相几乎平行分布,有些部分破碎,β相仅产生动态回复。等轴组织中的α相织构强度略有增加,片层组织中α相织构强度显著增加;而等轴和片层组织中β相织构强度均降低。同时,等轴组织力学性能各向异性很小,片层组织各向异性明显。600 ℃退火后,片层组织的α和β相织构强度均降低,力学性能的各向异性显著降低。     

退火对冷轧Cu-Ag合金组织及性能的影响

采用扫描电镜、透射电镜、拉伸试验机和热电性能分析系统等研究了退火对Cu-24%Ag合金显微组织、力学性能以及电学性能的影响,通过构建电子界面散射模型对合金导电机制进行了研究。结果表明,通过退火对Cu-24%Ag合金的显微组织进行了有效调控,改善了其综合性能。与冷轧态相比,合金经350 ℃退火1 h后,抗拉强度下降至冷轧态的95%,合金导电率提升了4%IACS。经450 ℃退火1 h,由于Ag纤维的溶解,合金的抗拉强度显著下降,只有冷轧态的一半左右;Ag纤维的溶解降低了电子的散射几率,使得导电率大幅度提升。因此,合金在350 ℃退火1 h后综合性能最佳,其抗拉强度和导电率分别为622 MPa和81%IACS。     

退火温度对船用Al-Mg-Mn-Cr合金组织和性能的影响

通过力学性能测试、光学显微镜及腐蚀性能测试等手段,研究了不同退火温度对实际生产的5AN6铝合金板材组织和性能的影响。结果显示:合金在退火后力学性能持续下降,于280 ℃退火时强度发生大幅度下降;在300~360 ℃退火时,合金力学性能趋于稳定;原始状态合金的晶粒组织为不完全的纤维组织,在280 ℃退火之后晶粒明显细化,可认为合金在280 ℃退火后发生了再结晶;5AN6铝合金的腐蚀性能温度敏感区间为160~240 ℃,在此温度区间内显微组织显示为沿晶界连续析出的β相。     

电线电缆用Al-Fe-Cu-0.25La-Zr耐热合金的导电性能

采用导电率测试仪、万能拉伸试验机、光学显微镜等分别测试了Al-Fe-Cu-0.25La-Zr合金的导电率、抗拉强度、伸长率等性能指标及显微组织,研究了电线电缆Al-Fe-Cu-0.25La-Zr合金在不同退火工艺下的导电性能与力学性能。结果表明,合金在350 ℃×2 h退火时达到导电率峰值62.8%IACS,抗拉强度为101.5 MPa,伸长率为32.4%;在300 ℃退火2 h时导电率达到62.1%IACS,抗拉强度为125.0 MPa,伸长率为13.4%。合金在300 ℃×(4~10) h退火期间,合金的导电率维持相对稳定,且高于350 ℃×(4~10) h,说明合金在300 ℃时具有更好的耐热稳定性。Al-Fe-Cu-0.25La-Zr合金最优的退火工艺为300 ℃×2 h,此工艺处理后的合金线材符合对电线电缆电学性能与力学性能的标准要求,且可以降低生产成本。     

退火温度对TA6合金板材组织和性能的影响

在不同温度下对TA6合金冷轧态板材保温60 min后空冷退火处理,研究退火温度对TA6合金板材组织和性能的影响。结果表明,冷轧后的TA6合金板材,在650℃以下退火时,其组织和性能变化很小;在700℃退火时开始发生再结晶,组织和性能出现明显变化;在720~800℃之间退火时,板材的力学性能已趋于稳定。TA6合金板材合理的退火工艺为(750~800)℃×60 min后空冷。     

变形与热处理对Invar合金组织及性能的影响

针对实际生产中Invar合金抗跌落性能差的问题,对Invar合金试样进行了不同温度(800℃、900℃、1000℃)的退火、不同变形量的冷变形及不同温度(500℃、600℃)的二次退火试验,并进行了显微组织观察和力学性能试验,分析各种工艺参数对Invar合金的组织和性能的影响。结果表明,经800℃退火 23％变形 500℃二次退火处理的Invar合金具有最佳综合性能。     

一种Al-Mg-Si合金板材退火工艺研究

试验研究不同加工率、退火温度和退火保温时间及退火冷却方式对一种Al-Mg-Si合金板材组织和性能的影响。通过力学性能检测、金相组织观察和X射线检验等手段,确定了该合金O状态板材的退火工艺为最佳退火温度范围380℃~400℃,退火保温时间1 h~2 h;退火冷却方式为空冷。按上述工艺参数,在工业性生产条件下生产出了力学性能和组织均满足研制目标要求的板材。     

超高强铝合金Al-7.88Zn-2.05Mg-1.70Cu-0.19Er薄带的组织与性能

研究了Al-7.88Zn-2.05Mg-1.70Cu-0.19Er合金薄带的组织、力学性能和耐腐蚀性能。结果表明,对厚度为0.5 mm的冷轧态薄带试样进行475 ℃/1 h/水冷固溶处理及120 ℃/6 h+150 ℃/24 h双级时效处理后,薄带合金具有优良综合性能,其硬度、极限抗拉伸强度、屈服强度和伸长率分别为1859.1 MPa、669.4 MPa、624.1 MPa和11.2%,该力学性能与峰值时效态合金的力学性能相当。该状态下合金的电导率、剥落腐蚀等级和应力腐蚀敏感指数分别为35.5%IACS、EA和4.07%。细小的球状Al₃(Er,Zr)和η?相均匀分布在Al基体中,且大部分析出物与Al基体晶格共格。细小不连续分布的晶界析出η相是该合金具有较低应力腐蚀敏感性的主要原因。     

铜银合金导线的显微组织与性能

利用光学显微镜和X射线衍射仪表征TAg0.1铜银合金的显微组织,采用显微硬度计、电子万能试验机、电导率测量仪等设备研究TAg0.1合金的力学性能及电学性能,系统分析铜银合金导线成型工艺过程中挤压、拉拔及退火等工序对TAg0.1合金显微组织、力学性能和电学性能的影响。结果表明:拉拔处理后TAg0.1合金的强度和硬度较挤压态提高,但伸长率和电导率降低。经退火处理后,TAg0.1合金的强度和硬度值均减小,伸长率和电导率均增大。经挤压、拉拔、中间退火、拉拔的工艺后,获得的TAg0.1空心导线硬度值为129.7 HV0.05、抗拉强度为400 MPa、导电率为99.5%IACS。     

GH4698合金的热处理

针对GH4698合金提出了一种新的热处理工艺：再结晶退火+标准热处理制度,即：980 ℃×4 h空冷+1100 ℃×8 h空冷+1000 ℃×4 h空冷+775 ℃×16 h空冷+700 ℃×16 h空冷。通过观察显微组织并测试合金的残余应力,研究了再结晶退火对组织和性能的影响。试验结果表明,再结晶退火能够有效改善合金的微观组织不均匀性,释放合金内部残余应力,降低后续热处理过程中的晶粒异常长大,从而显著提高GH4698合金的高温力学性能,且保持室温力学性能不变。     

Hot rolling characteristics of spray-formed AZ91 magnesium alloy

AZ91 magnesium alloy was prepared by spray forming. The spray-deposited alloy was subsequently hot-rolled with a 80% reduction at 350℃. The microstructural features of the as-spray-deposited and hot-rolled alloy were examined by optical microscopy, scanning electron microscopy and X-ray diffractometry. The results show that the spray-formed AZ91 magnesium alloy has, compared with the as-cast ingot, a finer microstructure with less interrnetallic phase Mg17Al12 dispersed in the matrix due to fast cooling and solidification rates of spray forming process, and, therefore showing excellent workability. It can be hot-rolled with nearly 20% reduction for one pass at lower temperatures （330-360℃）, and the total reduction can reach 50% prior to annealing. After proper thermo-mechanical treatment, the spray-formed AZ91 magnesium alloy exhibits outstanding mechanical properties.     

Effect of powerful current pulses on the structure and mechanical properties of the aluminum alloy Al-6%Mg-0.6%Mn

Changes in the microstructure and mechanical properties of commercial aluminum alloy Al-6%Mg-0.6%Mn after recrystallization have been studied. This alloy was recrystallized by two methods: annealing in air at temperatures of 250 to 450 °C for 20 min in an electrical resistance furnace; and passing an electrical current pulse by discharging a bank of capacitors (with a duration of about 100 μs). It is shown that electrical pulsed treatment produced a fine-grained structure in the Al-6%Mg-0.6%Mn alloy with a grain size (2–3 μm) smaller than the one annealed in the furnace and improved the mechanical properties of this material.     

Effect of elevated-temperature annealing on microstructureand properties of Cu−0.15Zr alloy

Cu−0.15Zr (wt.%) alloy with uniform and fine microstructure was fabricated by rapid solidification followed by hot forging. Evolution of microstructure, mechanical properties and electrical conductivity of the alloy during elevated-temperature annealing were investigated. The alloy exhibits good thermal stability, and its strength decreases slightly even after annealing at 700 °C for 2 h. The nano-sized Cu₅Zr precipitates show significant pinning effect on dislocation moving, which is the main reason for the high strength of the alloy. Additionally, the large-size Cu₅Zr precipitates play a major role in retarding grain growth by pinning the grain boundaries during annealing. After annealing at 700 °C for 2 h, the electrical conductivity of samples reaches the peak value of 88% (IACS), which is attributed to the decrease of vacancy defects, dislocations, grain boundaries and Zr solutes.     

Structure and Properties of Ti-19.7Nb-5.8Ta Shape Memory Alloy Subjected to Thermomechanical Processing Including Aging

In this work, the ternary Ti-19.7Nb-5.8Ta (at.%) alloy for biomedical applications was studied. The ingot was manufactured by vacuum arc melting with a consumable electrode and then subjected to hot forging. Specimens were cut from the ingot and processed by cold rolling with e = 0.37 of logarithmic thickness reduction and post-deformation annealing (PDA) between 400 and 750 °C (1 h). Selected samples were subjected to aging at 300 °C (10 min to 3 h). The influence of the thermomechanical processing on the alloy’s structure, phase composition, and mechanical and functional properties was studied. It was shown that thermomechanical processing leads to the formation of a nanosubgrained structure (polygonized with subgrains below 100 nm) in the 500-600 °C PDA range, which transforms to a recrystallized structure of β-phase when PDA temperature increases. Simultaneously, the phase composition and the β → α″ transformation kinetics vary. It was found that after conventional cold rolling and PDA, Ti-Nb-Ta alloy manifests superelastic and shape memory behaviors. During aging at 300 °C (1 h), an important quantity of randomly scattered equiaxed ω-precipitates forms, which results in improved superelastic cyclic properties. On the other hand, aging at 300 °C (3 h) changes the ω-precipitates’ particle morphology from equiaxed to elongated and leads to their coarsening, which negatively affects the superelastic and shape memory functional properties of Ti-Nb-Ta alloy.     

The Mechanical and Microstructural Changes of Sn-Ag-Bi Solders with Cooling Rate and Bi Content Variations

The purpose of this study is to investigate the influence of cooling rate and Bi addition on the microstructure evolution and mechanical properties of Sn-3.5Ag alloy. A series of Sn-3.5Ag-xBi solders has been fabricated with Bi content in the range of 0.5-3.5 wt.%. After solution heat treatment at 170 °C for 24 h and subsequent aging heat treatment at 100 °C for 2 h, samples were divided into two groups. One group was rapidly quenched into iced water (water quenching) for the fast cooling rate (20 °C/s), while the second group was slowly cooled (furnace cooling) in the furnace for the slow cooling rate (0.2 °C/s) after the furnace reflow. The microstructural evolutions of the present solders have been investigated using x-ray diffraction and scanning electron microscopy. The microhardness was measured to correlate the mechanical properties to alloy compositions and cooling rate. It was found that the microhardness of Sn-3.5Ag-xBi solders increased with increasing cooling rate. The indentation creep curves have been evaluated from the obtained microhardness values. Results revealed the steady-state creep rate decreased with increasing Bi content exhibiting an anomalous behavior at 2.5Bi. The reason for improved creep resistance of Sn-3.5Ag-xBi solders is the result of the combination of the solid solution strengthening and precipitation strengthening of Bi. The mean values of stress exponent indicated that the operative creep mechanism is dislocation climb.     

Effect of Holding Pressure on Microstructure and Mechanical Properties of A356 Aluminum Alloy

In this study, the effect of holding pressure on microstructure and mechanical properties of low-pressure die cast A356 aluminum alloy was investigated. The results showed that the application of high holding pressure (300 kPa) generated castings with denser structure and superior mechanical properties. By increasing the holding pressure up to 300 kPa, the size of secondary dendrite arm spacing greatly reduced by 22.7% at the cooling rate of 1°C/s and decreased by 12.8% at 10°C/s. The Feret’s diameter and aspect ratio of eutectic silicon particles decreased by 8.4 and 5.1% at the cooling rate of 1°C/s and decreased by 9.3 and 6.4% at 10°C/s, respectively. Meanwhile, the density of A356 aluminum alloy increased to 2.678 g/cm³ and the area fraction of porosity decreased to 0.035%. Thus, tensile properties of A356 aluminum alloy obtained at high holding pressure were enhanced, especially the ductility. All these could be associated with the better filling capability and faster cooling rate caused by high holding pressure. In the analytical range of experimental conditions, the correlation of mechanical properties with process parameters was established by statistical models to predict the ultimate tensile strength and elongation of low-pressure die cast A356 aluminum alloy.     

Effects of thermal exposure on the microstructure and properties of a γ-TiAl based alloy containing 44Al–4Nb–4Zr–0.2Si–0.3B

The microstructural stability after long-term aging at 700°C of a TiAl-based alloy containing 44Al–4Nb–4Zr–0.2Si–0.3B (in at%) has been studied. The microstructural observations are consistent with those established previously, i.e. even as low as 700°C the microstructure is unstable in that after prolonged aging, decomposition of the α₂ lamellae and increased volume fraction of gamma phase have been observed. Despite this, it has been shown that, with a combination of slow cooling from the annealing temperature and a ‘stabilisation’ treatment at an intermediate temperature, the mechanical properties of this alloy can be retained. This increase in thermal stability has been attributed to the large α₂ lamellae which result from slow cooling and are less susceptible to complete dissolution during aging, and also to the formation of gamma grains which are embedded in and constrained by the ω phase between the lamellar colonies. ©     

Influence of cooling rate after homogenization on microstructure and mechanical properties of aluminum alloy 7050

The influence of cooling rate (0.009?C220 °C/s) after homogenization on the microstructure and mechanical properties of high strength aluminum alloy 7050 was investigated by tensile testing, optical microscope, X-ray diffraction, scanning electron microscope, and transmission electron microscope. A lower cooling rate after homogenization resulted in lower mechanical properties after aging. The drop in strength was significant when the cooling rate was decreased from 0.5 °C/s to 0.1 °C/s. A lower cooling rate gave rise to a larger amount of remnant S(Al₂CuMg) phase and a higher fraction of recrystallization after solution heat treatment. Consequently, the increase in strength after aging due to precipitation hardening and substructure hardening was less significant in the case of slow cooling. This was supposed to be responsible for the lower mechanical properties due to a lower cooling rate after homogenization.     

Annealing effects on the microstructure and properties of bulk high-entropy CoCrFeNiTi0.5 alloy casting ingot

Most previous researches focused on small casting ingots prepared by arc melting, when studying high-entropy alloys. Large sized ingots were also necessary in exploring the existence of volume effects in the multi-principal element alloys. During the experiments, a large sized CoCrFeNiTi_0.5 alloy casting ingot was prepared by a medium frequency induction melting furnace. A slight volume effect occurred, reflecting mainly in the growth of crystalline grains and the increase of alloy hardness in the ingot. To investigate the effect of annealing temperature on microstructure and properties of CoCrFeNiTi_0.5 alloy, several samples taken from the ingot were annealed at 600 °C, 700 °C, 800 °C and 1000 °C respectively for 6 h. Almost no effects were found to the crystalline structure and elemental distribution when the samples were annealed below 1000 °C. The crystalline structure of CoCrFeNiTi_0.5 alloy was composed of one principal face-centered cubic (FCC) solid-solution matrix and a few intermetallic phases in the form of interdentrite. Dendrite contained approximately equivalent amount of Co, Cr, Fe, Ni and a smaller amount of Ti. When annealed below 1000 °C, the interdendrite stayed in (Ni, Ti)-rich phase, (Fe, Cr)-rich phase and (Co, Ti)-rich phase. After 1000 °C annealing, (Co, Ti)-rich phase disappeared, while (Ni, Ti)-rich phase and (Fe, Cr)-rich phase grew. The microhardness of the as-cast CoCrFeNiTi_0.5 alloy was 616.80 HV and the macrohardness was 52 HRC. The hardness of the samples stayed generally unchanged after annealing. This indicated a high microstructure stability and excellent resistance to temper softening that the CoCrFeNiTi_0.5 alloy exhibited.     

流变轧制AZ91合金的热处理和组织性能调控

本文对连续流变轧制AZ91合金在热处理过程中的组织和力学性能演化进行了研究。热处理后两种析出相在基体中出现：一种是晶界处的非连续析出相,另一种是从过饱和基体中析出的小尺寸连续析出相。随着时效温度升高,原子扩散速度也随之提高,导致更多的析出相生成和长大。合金的维氏硬度和拉伸强度峰值在16小时时效后出现,而合金的延伸率随着时效时间的延长和时效温度的提高呈下降趋势。经过对实验结果的分析,适合提升合金综合力学性能的热处理制度为415°C固溶20小时加220°C时效16小时。经热处理后得到的维氏硬度、拉伸强度和延伸率分别为：99 HV,251 MPa和4.5%,各项性能均显著优于流变轧制态合金。相对于传统成型手段,流变轧制加热处理方法成型的AZ91合金展现了优异且均衡的综合力学性能。