Microstructure and properties of Al-0.70Fe-0.24Cu alloy conductor prepared by horizontal continuous casting and subsequent continuous extrusion forming

A novel process for manufacturing A1-0.70Fe-0.24Cu alloy conductor was proposed, which includes horizontal continuous casting and subsequent continuous extrusion forming （Conform）. The mechanical properties, electrical conductivity and the compressed creep behaviour of the alloy were studied. The results indicate that the Conform process induces obvious grain refinement, strain-induced precipitation of AI7CuzFe phase and the transformation of crystal orientation distribution. The processed alloy has good comprehensive mechanical properties and electrical conductivity. Moreover, a better creep resistance under the conditions of 90 ~C and 76 MPa is shown compared with pure A1 and annealed copper, and the relationship between primary creep strain and time may comply with the logarithmic law. The enhanced properties are attributed to the grain refinement as well as the fine and homogeneously distributed thermally stable A1Fe and A17Cu2Fe precipitation phases.

Microstructure evolution and mechanical properties of the Sip/Zn- Al composite joints by ultrasonic-assisted soldering in air

Hypereutectic Al -27Si alloys were joined without flux by ultrasonic-assisted soldering at 420 ℃ in air using Zn -5Al the filler alloys, and Si particulate-reinforced Zn - Al based composites filler joints were obtained. The ultrasonic vibration introduced into soldering could influence the migration of Si particles and the microstructure of solidified Zn - Al based alloys. Both the distribution of Si particles and microstructure of the solidified Zn - Al based alloys affected the shear strength of joints. The shear strength increased with the ultrasonic vibration time. The highest average shear strength of joints reached to -68.5 MPa. Transcrystalline rupture mode was observed on the fracture surface.

Microstructure and mechanical properties of similar and dissimilar metal gas tungsten constricted arc welds:Maraging steel to 13-8 Mo stainless steel

Maraging steel (250) and 13-8 Mo stainless steel plates were joined by gas tungsten constricted arc welding(GTCAW) process in similar and dissimilar metal combinations using 13-8 Mo stainless steel filler wire. The similar and dissimilar metal welds made in solutionized condition were subjected to standard post weld hardening treatments direct ageing at 485 ℃, soaking for 31/2 hours followed by air cooling(ageing treatment of maraging steel) and direct ageing at 510 ℃, soaking for 4 h followed by air cooling(ageing treatment of 13-8 Mo stainless steel). The joint characterization studies include microstructure examination, microhardness survey across the weldments and transverse weld tensile test.Similar and dissimilar metal weldments responded to both the post weld ageing treatment. After post weld aging, increase in yield strength, UTS and slight reduction in % elongation of similar and dissimilar metal were observed. The observed tensile properties were correlated with microstructure and hardness distribution across the welds.

Properties and Microstructure Evolution of Al_2O_3-Si Material Fired in Different Atmospheres

A1203-Si composite specimens were prepared using fused corundum, ultra-fine α-A1203 and Si powder as starting materials and resin as binder. Effects of sintering atmospheres on properties, phase composition and microstructure of specimens after firing at 1 500 ℃ were investigated. The results show that： （ 1 ） after .firing in oxidizing or weak oxidizing atmosphere, there is some Si in the specimens and some glass phases containing mullite form on specimen surface, the density and strength at room temperature are relatively high, but hot modulus of rupture and thermal shock resistance are relatively poor; （2） after firing in, weak reducing or reducing atmosphere, Si reacts completely with CO or N2forming whisk-phere, Si reacts completely with CO or N2forming whisk-er-like SiC, granular Si2N20 or 0＇-SiAION, and the er-like SiC, granular Si2N20 or O＇-SiMON, and the thermo-mechanical properties of specimens are enhanced;（3） after firing in nitrogen atmosphere, Si reacts completely with N2, CO or G forming wbisker-like SiC and columnar β-SiA10N crystals, the hot modulus of rupture and thermal shock resistance of specimens are enhanced noticeably.

Effect of aging in an electric field on microstructures and properties of 1420 Al-Li alloy

After solution treatment, the 1420 Al-Li alloy samples were aged at different temperatures in an electric field with different intensity. The measurements made showed that the electric field increased the strength of the 1420 Al-Li alloy, and best properties were obtained when they were aged at 120 ℃ with E=4 kV/cm for 12 hrs. The electric field promoted the nucleation of δ′ phase, increased the quantity of the δ′ phase, and made the size of the δ′ phase particles smaller. The electric field restrained the formation and growth of PFZ, and increased the intensity of the electric field while the width of the PFZ was decreased.

Influence of Ca Element on Microstructure and Mechanical Properties of AZ61-1.2Y

The effects of Ca element on the microstructure and mechanical properties of AZ61-1. 2Y alloy were investigated by microstructure observation, tensile tests and fracture analysis. The results show that, with the addition of Ca element, the microstructure of AZ61-1.2Y was obviously refined, high melting point Al2Ca intermetallic compound formed, and/3-Mg17 Al12 phase disappeared. With 1. 0% Ca addition, the values of tensile strength at 25, 150 and 175 ℃ reached their maxima simultaneously, 225, 182, and 175 MPa, respectively. Meanwhile, the values of elongation at room temperature and elevated temperature were also up to their peaks. The enhancement of the mechanical properties of AZ61-1.2Y with Ca can be attributed to the functions of grain refmement strengthening and dispersion strengthening.

Effect of Heat Treatment on Mechanical Properties and Microstructure of NST 37-2 Steel

Engineering materials, mostly steel, are heat treated under controlled sequence of heating and cooling to alter their physical and mechanical properties to meet desired engineering applications. In this study, the effect of heat treatment (annealing, normalising, hardening, and tempering) on the microstructure and some selected mechanical properties of NST 37-2 steel were studied. Sample of steel was purchased from local market and the spectrometry analysis was carried out. The steel samples were heat treated in an electric furnace at different temperature levels and holding times;and then cooled in different media. The mechanical properties (tensile yield strength, ultimate tensile strength, Young’s modulus, percentage reduction, percentage elongation, toughness and hardness) of the treated and untreated samples were determined using standard methods and the microstructure of the samples was examined using metallographic microscope equipped with camera. Results showed that the mechanical properties of NST 37-2 steel can be changed and improved by various heat treatments for a particular application. It was also found that the annealed samples with mainly ferrite structure gave the lowest tensile strength and hardness value and highest ductility and toughness value while hardened sample which comprise martensite gave the highest tensile strength and hardness value and lowest ductility and toughness value.

Microstructural evolution and its effect on mechanical properties in different regions of 2219-C10S aluminum alloy TIG-welded joint

Microstructural evolution and its effect on mechanical properties in different regions of 2219-C10S aluminum alloy tungsten inert gas(TIG)welded joint were analyzed in detail.In weld zone(WZ),α+θeutectic structure formed at grain boundaries with no precipitates inside the grains.In partially melted zone(PMZ),symbiotic eutectic or divorced eutectic formed at grain boundaries and needle-likeθ′phases appeared in the secondary heated zone.In over aged zone(OAZ),the coarsening and dissolution ofθ′phases occurred and mostθ′phases transformed intoθphases.In general heat affected zone(HAZ),θ′phases coarsened.Factors such as the strengthening phases,the grain size,the Cu content in matrix and the dislocation density can affect the mechanical properties in different regions of the joint.Moreover,a model describing the relationship between mechanical properties of the material and the volume fraction of precipitates,the average diameter of precipitates and the concentration of soluble elements was proposed.

Effects of Resins with Different Molecular Structures on Properties of MgO-C Bricks

Resins PFG-4 , PFG-8 and a reference resin （resin A） were used as binders of MgO - C bricks, effects of the resins with different molecular structures on wettability of magnesia, on physical properties, mechanical properties, oxidation resistance and thermal expansion properties of MgO- C bricks were researched. The results show that the microstructures of solidified resins with different mo- lecular structures are different, which have obvious effect on the cold mechanical properties of MgO - C brick, but little effect on the oxidation resistance, thermal perform- ance and expansion properties.

Effect of Heat Treatment on Gradient Microstructure and Tensile Property of Laser Powder Bed Fusion Fabricated 15-5 Precipitation Hardening Stainless Steel

This work investigated the gradient microstructure evolution and tensile property of LPBF fabricated 15-5 precipitation hardening stainless steel in post-process direct ageing(DA)and solution treating&ageing(STA).The varied microstructures for austenite and small-sized oxide inclusions at different sample heights in the as-built(AB)condition was generally preserved after DA treatment.However,austenite was almost disappeared,and oxide particle grew significantly after the STA treatment.As a result,the tensile property differences in sample top and bottom for AB and DA conditions did not occur in the STA samples.For the influence of post-process heat treatment,the STA condition had the highest yield strength due to the highest volume fraction of nano-sized Cu precipitates.However,the DA specimen had the highest ultimate tensile strength and elongation owing to the considerable amount of austenite phase and associated transformation induced plasticity effect.

Ti-Al基合金中的Hall-Petch关系及影响因素分析

研究了全层片状组织Ｔｉ－Ａｌ基合金的室温拉伸性能与品团尺寸的关系Ｔｉ－Ａｌ基合金的室温拉伸屈服强度和断裂强度与晶团尺寸成 Ｈａｌｌ－Ｐｅｔｃｈ关系．当合金中添加替代元素 Ｃｒ和 Ｎｂ时、具 Ｈａｌｌ－Ｐｅｔｃｈ斜率下变：而添加间隙元素 Ｃ和 Ｂ时。

高温后HVFA-SHCC的单轴压缩力学性能及本构关系

采用40mm×40mm×160mm棱柱体试件,研究了高温后大掺量粉煤灰-应变硬化水泥基复合材料(HVFA-SHCC)的单轴压缩力学性能,探讨了不同目标温度(100、200、400、600、800℃)和不同冷却方式(自然冷却、浸水冷却)条件下HVFA-SHCC试件抗压强度、弹性模量、压缩韧性、破坏模式及质量的变化.采用扫描电子显微镜(SEM)对试件的微观结构进行分析,获得了高温后HVFA-SHCC单轴压缩性能的劣化机理.结果表明:当温度低于200℃时,温度对试件力学性能及质量损失的影响较小;400~800℃时,试件内部结构变得疏松,残余力学性能劣化严重,尤其是800℃时,试件的抗压强度仅为常温状态的39.9%,弹性模量为常温状态的32.3%,压缩韧性指数为常温状态的59.0%,质量损失率达15.5%;浸水冷却试件的残余力学性能得到了一定程度的提高.同时,基于试验结果,建立了高温后HVFA-SHCC的单轴压缩本构方程.

Microstructures and mechanical properties of AZ31-0.1Ca magnesium alloy produced by soft-contact electromagnetic casting and hot extrusion

An AZ31-0.1Ca magnesium alloy produced by Soft-contact electromagnetic continuous casting （SEMC） was investigated. The fine homogeneous structure and the precipitated phases were obtained by SEMC. The effects of microalloying of Ca and middle frequency electromagnetic field on AZ31-0.1Ca magnesium alloy were discussed. And the as-cast billets were extruded with different extrusion ratios subsequently. The alloy showed an ultrafine grain size of 2-5 #m due to dynamic recrytallization （DRX） in the course of hot extrusion. The comprehensive properties of the as-extruded alloy are the best at the extrusion ratio of 25, and the hardness, UTS and elongation are 73.9 HB, 356.8 MPa and 16.570, respectively.

Diffusion bonding behaviour of β-γTiAl alloys containing high niobium with Ti interlayer by spark plasma sintering

High niobium β-γ TiAl alloy(HNBG) was diffusion bonded using spark plasma sintering with pure Ti as interlayer. The joint microstructural evolution, growth kinetics and mechanical properties were investigated. The joint included three diffusion zones. The β/B2 phase formed in the Zone Ⅰ, α_(2)phase in the Zone Ⅱ, and β-Ti and α-Ti phases in the Zone Ⅲ. The thickness of β/B2 phase, the average grain size of α_(2)phase and the amount of β-Ti phase increased with the increase of bonding temperature or bonding time. The growth activation energies of β/B2 and α_(2)phases were 582 and 253 kJ/mol, respectively. The joint acquired at 1000 °C, 10 min and 10 MPa showed the maximum shear strength of 308 MPa. Fracture mainly occurred along the interfaces between Zone Ⅰ and HNBG alloy, and between Zone I and Zone Ⅱ. Fracture mechanism of the joint was characterized by brittleness rupture along the phase boundary.

镁合金FSW接头微观结构演化与组织、性能的关联性

为了研究AZ31镁合金FSW过程中的微观结构演化与组织、性能间的关联性,采用Monte Carlo和试验相结合研究焊接区域微观结构演化,测试焊接区的组织与性能,构建微观结构演化和组织、性能间的Hall-Petch关系式。结果表明:AZ31镁合金的FSW前进侧和后退侧硬度的最小值均在搅拌针和轴肩之间的覆盖区域,且后退侧材料硬度较前进侧稍高。搅拌头转速增加时,镁合金FSW搅拌区晶粒增大,说明搅拌头旋转导致的温度变化对搅拌区的晶粒形貌变化具有重要影响。随着搅拌头转速的增加,镁合金FSW温度升高,同时应变率随之增加,温度升高导致晶粒变大,应变率增加导致形核率增加从而导致晶粒变小,综合作用的结果使搅拌头转速增加时镁合金FSW搅拌区晶粒随之增大。

TC4合金的新型本构关系

通过热态模拟试验 ,系统地研究了主要锻造热力参数 (变形速度、变形温度、变形程度 )与 TC4合金流动应力、微观组织之间的数值关系 ,采用数理统计原理 ,科学地分析并回归出了能综合反映锻造热力参数和微观组织演化过程对材料成形性能影响的本构方程 ,定性地探讨了各热力参数对 TC4合金组织和性能的影响规律 ,为TC4合金锻造过程的数值模拟和锻造热力参数的合理制订与控制提供了基础。

2524铝合金的蠕变时效行为

采用拉伸测试、维氏硬度测试和透射电镜分析等方法研究实验应力和时效时间对2524铝合金蠕变时效行为的影响。结果表明:时效时间和试验应力对材料的成形与微观组织均有较大的影响,应力越大、时间越长,蠕变行为越明显;在190℃温度下,试验应力为180 MPa,时效时间约为12 h时,材料的硬度和强度趋近于峰值;TEM分析表明,合金板材强度和伸长率的差别主要由时效后强化相S′相和S″相的尺寸和分布密度决定;采用线性回归方法获得合金在190℃下稳态蠕变速率与实验应力的本构关系。

超高温氧化物共晶复合陶瓷研究进展

超高温氧化物共晶复合陶瓷具有优异的力学性能、高温组织稳定性、抗氧化和抗腐蚀性能,被认为是1400℃以上高温富氧环境长时稳定服役的理想高温结构材料,近年来受到世界各国学者的广泛关注。系统介绍了氧化物共晶复合陶瓷的发展现状,对近年来本领域取得的重要进展进行了总结和分析,同时结合作者在本领域的研究,重点阐述了超高温度梯度定向凝固氧化物共晶复合陶瓷的组织特征、凝固特性、以及晶体取向/结构特征和力学性能,最后对氧化物共晶复合陶瓷今后的发展趋势和突破点进行了展望。

基于晶体学原理的高效光催化材料的设计与制备

光催化技术是一种将太阳能转换为化学能的新技术,基于该技术可利用半导体光催化材料实现光催化分解水制氢、二氧化碳还原制备有机物、降解有机污染物等,是解决未来能源和环境问题的潜在途径之一。然而,作为光催化技术的核心,光催化材料面临着光吸收范围窄、光生载流子分离效率低等问题,这些问题严重制约着光催化能量转化效率及其实际应用。针对制约光催化材料活性的关键科学问题,近年来本课题组从晶体学基本原理出发,基于半导体材料结构与性能的关系,通过对半导体材料的晶体结构、电子结构、微结构参数进行设计与调控,探索制备了一系列具有宽光谱响应范围、高载流子分离效率的新型高效光催化材料,为设计制备新型高效光催化材料提供了一些新的设计思路和材料制备方法。

SiCp/A390复合材料中析出相的形貌及界面结构演变

采用快速凝固的A390铝合金粉体和SiC颗粒,通过粉末冶金法+热挤压工艺制备了SiCp/A390复合材料,并对复合材料进行了T6处理,利用扫描电镜(SEM)、透射电镜(TEM)及高分辨透射电镜(HRTEM)对复合材料时效过程中第二相的析出形貌及界面结构进行了表征,测定了复合材料的力学性能,探讨了析出相的演变规律、析出相与基体的界面结构及其对力学性能的影响。结果表明:SiCp/A390复合材料经固溶+时效处理后,合金元素从基体中析出形成GP区,然后转变为颗粒状的δ″相。随着时效时间的延长,这些颗粒状δ″相继续长大成δ'相和δ相;同时,时效析出相与基体之间界面结构随时效时间的延长发生着转变,其转变规律为:完全共格界面GP区→共格界面的δ″相→半共格界面δ'相→非共格界面δ相;SiCp/A390复合材料的抗拉强度随着时效时间延长先增加后降低,在时效6 h时,复合材料的力学性能达到最大值。