受阻酚封端聚氨酯/环氧树脂共混物阻尼材料的结构与性能EI北大核心CSCD

制备了系列受阻酚封端聚氨酯/环氧树脂(EP)共混物阻尼材料,研究了组成比和云母对共混物动态力学性能和拉伸性能的影响。结果表明,EP的加入显著拓宽了阻尼温域和改善了阻尼性能,随着EP用量的增加,共混物的拉伸强度显著增加,但断裂伸长率降低。加入填料云母后,材料的阻尼性能和拉伸性能均有所提升。     

受阻酚封端聚氨酯/环氧树脂共混物阻尼材料的结构与性能

制备了系列受阻酚封端聚氨酯/环氧树脂(EP)共混物阻尼材料,研究了组成比和云母对共混物动态力学性能和拉伸性能的影响。结果表明,EP的加入显著拓宽了阻尼温域和改善了阻尼性能,随着EP用量的增加,共混物的拉伸强度显著增加,但断裂伸长率降低。加入填料云母后,材料的阻尼性能和拉伸性能均有所提升。     

高阻尼宽温域粘弹性硅橡胶复合材料的制备及性能研究

以硅橡胶和丁基橡胶为基体材料,成功制备出高阻尼宽温域粘弹性硅橡胶复合材料,最大损耗因子tanδmax>0.3≥0.7,损耗因子大于0.3的温度范围△Ttanδ≥100℃.同时研究了材料的力学性能、阻尼性能和相态结构.结果表明,在硅橡胶基质中,加入具有一定相容性的高阻尼丁基橡胶材料,可以显著提高体系的阻尼因子,拓宽有效阻尼温度范围.补强剂白炭黑的加入可以提高材料的机械力学性能,但对材料的阻尼性能产生一定的负面影响,通过加入一定量的硅烷偶联剂KH-845-5对白炭黑表面进行改性处理,可以部分有效解决这两种性能间的矛盾,达到高性能硅橡胶阻尼减振材料使用上的性能平衡.     

Si及时效对Fe-Al-Si阻尼合金性能的影响

为了进一步提高Fe-Al二元阻尼合金的阻尼性能和力学性能,并认识在较高温度下长时间使用对其阻尼性能的影响,利用倒扭摆、拉伸、光学金相等方法测试了微量Si元素和不同时效时间对Fe-Al基合金阻尼性能、力学性能、微观组织的影响.结果表明,在Fe-Al合金中添加少量Si元素,合金的阻尼性能、力学性能优于Fe-Al合金,晶粒也得到明显细化.350℃长时间时效前后,实验合金的阻尼性能、力学性能、微观组织保持稳定.Fe-Al-Si阻尼合金具有更加全面的阻尼和力学性能,并可在350℃下长时间使用,应用范围更广阔.     

结构-阻尼复合材料研究进展

航空航天飞行器的高速、轻质和多功能化的发展,精密电子仪器设备的应用及舒适性要求的提高,对传统结构材料的减重和降噪提出了巨大的挑战.近年来,随着纤维增强复合材料的在航空航天领域应用比重的迅速提升,开发兼具高力学性能和高振动阻尼性能的新型结构-阻尼多功能材料也成为研究的热点问题之一.本文在介绍结构-阻尼复合材料阻尼机理的基础上,综述了国内外关于结构阻尼复合材料主要研究内容及研究成果,并讨论了其今后的发展趋势,包括开发新的多功能阻尼插层材料、引入新的阻尼耗能机制、开发多层次结构模型和对阻尼性能和力学性能的多尺度模拟等.     

甲基乙烯基硅橡胶/丁基橡胶的阻尼性能与热稳定性研究

用共混-硫化法制备了甲基乙烯基硅橡胶/丁基橡胶(PMVS/IIR)复合材料,并采用拉伸测试和动态力学测试(DMA)、TG分析了材料的力学性能、阻尼性能和在空气中的热稳定性.结果表明,通过改变聚合物组分的配比和硫化剂的用量,可得到力学性能较好的复合材料.DMA测试表明,与硅橡胶相比,在以酚醛树脂作为硫化剂时,复合材料的阻尼温域从0℃拓宽到近150℃(-50～100 ℃),阻尼因子从0.12提高到0.69.所制备出的材料可作为阻尼材料使用.     

高应变率下阻尼铝合金的动态力学性能研究

针对航空用高阻尼铝合金在高应变率载荷下的服役特征,研究了两种高阻尼铝合金在高应变率下的动态力学性能.采用分离式霍布金森(Hopkinson)压杆对高阻尼铝合金进行了动态压缩实验,获得了应变率(140,275,500s-1)对材料应力-应变曲线的影响规律,并同普通铸造铝合金ZL101A的动态压缩力学性能进行比较分析.结果表明:高阻尼铝合金在高应变率下的力学性能明显优于普通铸造铝合金;第一种高性能阻尼铝合金的动态压缩力学性能优异.第二种高性能阻尼铝合金随着应变率的提高,材料的弹性模量和应力均有所下降,但是形变强化效果显著.     

高硅镍铜合金NCu30-4-2-1挤压棒材的研制

对高硅镍铜合金NCu30-4-2-1进行了短时高温拉伸实验,研究了材料的强度和塑性随温度的变化规律.采用Gleeble-1500热模拟实验机对该合金铸态材料在不同变形温度和应变速率下进行了热压缩变形实验,研究了流变应力受温度和应变速率影响的变化规律,以及高温变形组织随温度和应变速率变化的规律.结合实际挤压实验,确定了合理的挤压温度和挤压速率范围.该合金的力学性能和挤压成材率得到了大幅度提高.     

PMN掺杂酯醚共聚聚氨酯压电阻尼材料的制备及其表征

通过溶液共混法制备了铌镁锆钛酸铅(PMN)掺杂酯醚共聚聚氨酯压电阻尼材料,并研究了PMN含量对材料阻尼性能、压缩生热、压电性能及力学性能的影响。结果表明,PMN可有效改善材料的阻尼性能,并且可以降低材料因阻尼效应而产生的温度升高,同时也可赋予材料一定的压电性,但当PMN含量过高时反而不利于材料阻尼性能和力学性能的提高。     

等径道角挤压制备高力学性能细晶Mg-6Al合金

为了制备高力学性能细晶Mg-6Al合金坯料,采用金相显微镜、材料拉伸实验机等手段对Mg-6Al合金铸坯进行等径道角挤压实验研究.并利用热处理工艺对挤压后材料进行处理,研究热处理工艺参数对材料力学性能的影响规律.结果表明,Mg-6Al合金的铸坯的抗拉强度为196.4MPa,延伸率为12.6%.经过等径道角挤压的Mg-6Al合金坯料的晶粒被大大细化,其晶粒尺寸由铸坯的140μm左右细化到8μm左右.其力学性能有很大提高,抗拉强度由196.4MPa提高到308.2MPa;延伸率由12.6%提高到30.6%.等径道角挤压工艺是一种非常好的制备高力学性能、细晶Mg-6Al合金的工艺方法.固溶和人工时效热处理工艺对等径道角挤压的Mg-6Al合金坯料的强度有较大影响,对延伸率影响较小.     

超细晶纯铝微观组织及力学和腐蚀性能研究

在室温下采用等通道转角挤压(ECAP)对工业纯铝(CP-Al)圆棒料进行12道次挤压,通过光学显微镜(OM)、X射线衍射(XRD)、扫描电子显微镜(SEM)、单向拉伸与电化学测试研究了超细晶纯铝的微观组织、力学性能和耐腐蚀性能.结果表明,ECAP后纯铝试样晶粒细化,4道次和8道次后晶粒尺寸分别达到576、482 nm.同时,显微硬度和抗拉强度显著提高,由初始的26.8 HV、79.2 MPa分别增加到8道次的48.3 HV、146.4 MPa,而塑性有所降低,断裂伸长率由初始的22.1%降低到4道次的9.5%.在质量分数为3.5%NaCl溶液中进行了开路电位(OCP)、极化曲线(PD)及电化学阻抗谱(EIS)测试,并观察腐蚀形貌.研究表明,随着ECAP道次的增加,腐蚀电位正移(-0.965~-0.860 V)、电荷传递电阻增大(1.741×10~4~4.798×10~4Ω·cm~2)、点蚀电位正移(-0.818~-0.734 V)、腐蚀电流密度降低(12.910~3.288μA/cm2),且腐蚀形貌有所改善,表明其耐腐蚀性能提高.这是由于随着挤压道次的增加,晶粒细化,加速了表面钝化膜的形成,形成的钝化膜更为致密,从而降低了腐蚀速率.     

T-shaped equi-channel angular pressing of Pb–Sn eutectic and its tensile properties

Equi-channel angular pressing (ECAP) of a Pb–Sn eutectic alloy up to six passes in a T-shaped die, rather than a conventional L-shaped die, was studied for grain refinement. The effect of ECAP on the hardness and tensile properties was studied. Microstructure predominately changed in the early part of the ECAP process and became equiaxed and uniformly distributed in both the longitudinal and the transverse sections after four passes. There occurred substantial softening over the first two passes—hardness of 10 Hv, yield strength of 14.2 MPa and tensile strength of 16.3 MPa in the as-cast condition decreased upon two passes to 6 Hv, 9.7 MPa and 13.0 MPa, respectively. The ductility (% elongation) increased drastically from <50% in the as-cast condition to 150% upon two passes, and further increased to 230% after four passes. Various tensile properties and concurrent microstructural evolution were used to develop a mutual relationship among them.     

Microstructure, mechanical properties and electrical conductivity of industrial Cu-0.5%Cr alloy processed by severe plastic deformation

Microstructure, mechanical properties and electrical conductivity of industrial Cu-0.5% alloy subjected to equal channel angular pressing (ECAP) by route A and cold rolling with and without aging treatment were investigated. The lamellar grains in thickness of 100 nm were obtained after eight ECAP passes. They were not further pancake shaped, but fragmentary and obtained less sharp boundaries with more dislocations in addition to cold rolling. After aging at 450 °C for 1 h, high density of dislocations and some coarse grains were observable after ECAP and the additional cold rolling, respectively. The tensile tests show that tensile strength arrived at 460 MPa and 484 MPa after four and eight passes of ECAP, respectively, the corresponding tensile strength increased to 570 MPa and 579 MPa after the additional cold rolling. However, the electrical conductivity was not more than 35% IACS. It was proved that four passes of ECAP followed by 90% cold rolling and aging at 450 °C for 1 h offered a short process for Cu-0.5%Cr alloy to balance the paradox of high strength and electrical conductivity, under which the tensile strength 554 MPa, elongation to failure 22% and electrical conductivity 84% of IACS could be obtained. The high strength was explained by precipitation strengthening and fine grain strengthening.     

Rissfortschritts‐ und Ermüdungsverhalten der Aluminiumlegierung EN AW‐6060 nach ECAP und nachgelagerter Wärmebehandlung

Crack growth and high cycle fatigue behaviour of an AA6060 aluminium alloy after ECAP combined with a subsequent heat treatment Crack growth properties of the Al‐Mg‐Si alloy AA6060 as well as the high cycle fatigue behaviour have been investigated after equal‐channel angular pressing (ECAP). In our study, experiments have been conducted on different stages of microstructural breakdown and strain hardening of the material as they were present after different numbers of ECAP passes. A bimodal condition, obtained after two pressings, and a homogeneously ultrafine‐grained condition after eight repetitive pressings have been investigated. Furthermore, optimized conditions with an enhanced ductility, produced by ECAP processing combined with a following short‐time aging treatment were included into the study. Crack growth experiments have been conducted in the near‐threshold regime and the region of stable crack growth, covering a range of load ratios from R = 0.1 up to 0.7. It was found that the lowered fatigue threshold ΔK_th of the as‐extruded material can be enhanced by the combination of ECAP and short‐time aging, owing to the increased ductility and strain hardening capability of this material. By means of SEM investigations and tensile tests, the crack growth properties of the different conditions were related to microstructural and mechanical features. In fatigue tests, load reversals up to failure and the fatigue limit for an as‐extruded condition and an optimized condition after two ECAP‐passes have been compared to the coarse grained initial condition and a remarkable increase in fatigue strength was noted.     

Effect of grain refinement on the mechanical properties of Cu–Al–Be–B shape memory alloy

In this work, the mechanical properties of equal channel angular processing (ECAP)-processed fine- and coarse-grained Cu–11.42Al–0.35Be–0.18B shape memory alloys (wt.%) were evaluated using tensile testing. After eight passes of ECAP and subsequently quenching from 600 °C to RT, the mean grain diameter was refined from 227 μm to 42 μm with grain boundaries purified. The fine-grained alloy exhibited good mechanical properties with a high tensile strength (703 MPa) and featured deeper and closer dimples on its fracture surface. The micro cracks were more refined, and the cracks extension along the grain boundaries was improved in the fine-grained alloy. These changes can be attributed to improvement of martensite morphology, structural refinement and grain boundary purification.     

Thermophysical Properties of Aluminum 1060 Fabricated by Equal Channel Angular Pressing

Equal channel angular pressing (ECAP) has the advantage of enabling an ultrafine grain size. Aluminum 1060 is used as a power plant material because of its favorable electrical properties. However, the weak strength of aluminum limits its application. In this study, the thermal conductivity and electrical conductivity of Al 1060 made by ECAP was investigated. ECAP was conducted through the die having a channel angle of 90° and a corner angle of 20° at a temperature of 473 K with a strain rate of 2 mm · s⁻¹. The specimen was then processed with 1 to 8 passes by the route Bc method with 90° rotation. In the case of eight passes, the grain size was reduced to as small as 300 nm. As a result of the ECAP, the tensile strength was raised from 75 MPa to 134 MPa, while the electrical conductivity did not show a significant difference after eight passes. The thermal conductivity gradually decreased with ECAP passes, because of the decreased grain size by ECAP.     

ECAP变形对Mg2Si增强耐热镁合金组织及性能的影响

为了提高镁合金的耐热性能,在Mg-Zn合金中加入Si,形成Mg-Zn-Si镁合金.采用ECAP工艺在变形温度为573 K和挤压路径为Bc条件下对Mg-Zn-Si镁合金进行不同道次的变形.运用金相显微镜(OM)、X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等手段对变形后的Mg-Zn-Si镁合金进行了组织表征,对变形后的合金进行了室温拉伸和高温蠕变等力学性能测试.结果表明:随着挤压道次增加,α-Mg基体、Mg Zn相及Mg2Si相均得到细化且分布趋于均匀.1道次挤压后部分基体α-Mg细化,4道次挤压后α-Mg的尺寸减小为5~10μm,且晶粒大小趋于均匀;2道次挤压后Mg2Si相枝晶在原位置破碎为颗粒状,6、8道次挤压后Mg_2Si相呈弥散分布.4道次挤压后合金的屈服强度和抗拉强度均提高120%,伸长率提高353%;8道次挤压后合金的抗拉强度和伸长率与4道次相比变化不大,但屈服强度进一步提高了19%.随着挤压道次增加,高温抗蠕变性能提高,8道次后高温稳态蠕变速率降低5倍.Mg2Si相细化机理为受剪切而机械碎断.     

Ultra-fine grained bulk CP-Ti processed by multi-pass ECAP at warm deformation region

In order to refine the grain size of commercially pure titanium (CP-Ti) to a submicrometer scale, equal channel angular pressing (ECAP) was attempted at a temperature range of 200–300 °C. The experiments revealed that, 250 °C was the minimum temperature at which ten passes of ECAP could be performed in a 105° die without the cracking of billets. An ultrafine-grained (UFG) microstructure with a mean grain size of 183 nm was achieved after 10 passes. The processed CP-Ti displayed high tensile strength of 892 MPa and high elongation to failure of 20.5%. The enhancement in mechanical properties is explained in terms of grain refinement and dislocation density increasing. The high ductility of UFG pure Ti with the absence of strain hardening behavior is attributed to its enhanced strain rate sensitivity.     

Effect of equal channel angular pressing on fracture toughness of Al-7075

In this paper, influence of equal channel angular pressing (ECAP) on the fracture behavior of Al-7075 alloy is experimentally investigated. The specimens are successfully processed by ECAP methodology up to four passes using different routes. Transmission electron microscope (TEM) images showed that after four passes of ECAP, the average grain size is refined from 40 μm to less than about 500 nm. The percentage increase in yield strength, ultimate strength and microhardness of the specimens after four ECAP passes was 230, 90 and 110 respectively. Standard tests on the disk-shaped compact DC(T) specimens showed that fracture toughness is decreased up to 8% at the first ECAP pass while after four passes, this parameter roused to 17% higher than that of annealed condition. Furthermore, scanning electron microscope (SEM) micrographs demonstrated that ductile fracture mechanism with large dimples occurred in the annealed samples, changed to limited ductile fracture with fine dimples after ECAP process. This research provides new insights into the effect of ECAP and grain refinement on the fracture behavior of materials.     

Effect of 1.5 wt% tin addition on the properties of AZ31 magnesium alloy

In this paper, 1.5 wt%Sn was added to the AZ31 magnesium alloy aiming at improving the mechanical properties by using a low cost alloying element. Both alloys were prepared in the cast/heat treated (HT), rolled at 350 °C, rolled/heat treated at 400 °C and extruded at 350 °C. The results indicate that with addition of tin an improvement was obtained in both tensile strength and ductility of the AZ31 alloy in the cast/heat treated and in the extruded conditions. The yield and ultimate tensile strengths reached 98 MPa and 224 MPa respectively with 14 % elongation in the cast/heat treated condition while in the extruded condition these values were 212 MPa and 286 MPa with 20 % elongation. The tensile strength was even higher after rolling reaching 315 MPa for AZ31 with tin addition; however, as the material temperature during the last passes has decreased to relatively low values, the % elongation decreased to 1 %. After heat treatment at 400 °C for 2 hours the % elongation was restored and reached 12 %; this was accompanied by a decrease in tensile strength which reached 276 MPa. The results are discussed in relation to the microstructure evolution including grain size, phase identification, and volume fraction of phases.