莫来石短纤维/Al-4.5Cu 复合材料的力学性能与断裂特征

采用挤压铸造法制造了莫来石短纤维/Al-4.5Cu 复合材料, 研究了不同挤压铸造工艺参数条件下其力学性能的变化规律和断裂特征。实验结果表明: 随着凝固冷却速率的提高, 莫来石短纤维/Al-4.5Cu 复合材料的抗弯强度和弹性模量相应逐渐增大; 另外, 挤压铸造莫来石短纤维/Al-4.5Cu 复合材料表现为脆性解理断裂, 当凝固速率较大, 复合材料强度较高时, 断口中局部有莫来石短纤维拔出; 同时, 各种凝固冷却速率条件下, 断裂面上均有少量韧窝存在。      

等轴晶移动条件下金属凝固温度场、流场及溶质分布数值模拟

本文利用作者提出的固相移动条件下金属凝固传热、传质及动量传输数学模型对砂型铸造 Al-4.5%Cu 合金铸锭凝固过程进行了数值模拟研究与试验验证。模拟冷却曲线及宏观偏析与试验结果基本相符。     

Al2O3/Al-Si合金复合材料凝固组织的研究

本文在国产氧化铝短纤维基础上,研究了氧化铝短纤维增强铝硅合金复合材料的凝固组织。研究结果表明,在复合材料凝固过程中,氧化铝短纤维可以为铝硅合金中硅相非自发形核的衬底,并有利于细化基体合金的晶粒和降低显微偏析程度。     

三维网络SiC/Cu金属基复合材料的凝固显微组织

用挤压铸造法制备了三维网络SiC/Cu金属基复合材料,研究了铸造压力、网络SiC骨架预热温度、浇注温度等工艺条件对复合材料凝固显微组织的影响.结果表明,三维网络SiC陶瓷骨架在晶体生长和结晶过程中有重要作用,在一定条件下在网孔内可形成垂直于骨架表面的枝晶网络,或形成粒度细小且分布均匀的等轴晶组织;骨架的孔径对显微组织的影响也很大,细小的孔径有利于晶粒细化和组织均匀化,粗大的孔径助长宏观偏析和铅的偏聚.骨架减轻了复合材料中锡的反常偏析,使锡的偏析主要发生在骨架表面附近的微小区域,从而避免了在铸件表层的集中偏析.     

残余形变对莫来石短纤维/Al-4.5Cu复合材料及其基体合金时效析出行为的影响

用挤压铸造法制备莫来石(mullite)短纤维/Al-4.5Cu复合材料及其基体合金。用硬度测试(HB)、差示扫描量热仪(DSC)和透射电镜(TEM),研究固溶淬火后残余形变(0 %,12.5 %,25 %,34.4%)和纤维对复合材料及其基体合金时效析出行为的影响。结果表明:形变对Al-4.5Cu合金的时效析出过程具有十分明显的加速作用,随着形变度增加,时效加速作用进一步加强;莫来石短纤维对Al-4.5Cu合金的时效析出过程具有加速作用;纤维和形变同时存在时,复合材料的时效析出过程还会进一步加快。但是,形变或/和纤维抑制了Al-4.5Cu合金中GP区的形成。     

快速凝固铸造合金中的偏析与组织

本文讨论了不同凝固速度下合金铸件与铸锭中,以至快速凝固的粉末或薄膜中的枝晶臂间距与偏析。以Al-4.5Cu作为例子。在这类工业合金的快速凝固中我们很少去注意不平衡现象。较多的倒是在于寻求途径以获得均匀、平衡的凝固组织。增大凝固速度可提高均匀性,它的作用包括:减少枝晶臂间距,降低树枝晶尖端温度,降低共晶生长温度,消除树枝晶,造成初生相或次生相形核前的过冷。     

微量Cu和形变热处理对Al-Fe合金性能的影响

观察Al-Fe合金的显微组织并测量其力学性能和导电性能,研究了Cu元素和形变热处理对其性能的影响。结果表明：在铸态Al-Fe-Cu合金组织中,Cu元素在基体内均匀分布,而Fe元素在晶界处偏析;挤压态的Al-0.7Fe-0.2Cu合金其性能最优：导电率为59.90%IACS,抗拉强度为108 MPa,硬度为31.2HV;随着退火温度的提高Al-0.7Fe-0.2Cu合金的抗拉强度急剧降低,在400℃退火时其抗拉强度最低(100 MPa),伸长率最高(31.3%);在250℃退火时导电率出现峰值(62.61%IACS)。在退火Al-0.7Cu-0.2Cu合金中有许多细小针状的θ(Al₂Cu)相析出,并与位错交互缠结。随着退火温度的提高合金中的位错密度降低,晶粒细化。     

短纤维增强铝铜二元合金复合材料凝固偏析的数值模拟

根据凝固过程中的守恒原理,建立了铝基复合材料凝固过程的数学模型.根据所建立的模型对氧化铝短纤维增强铝铜二元合金复合材料进行数值模拟,模拟结果表明:氧化铝短纤维周围有低熔点物质及溶质富集;随冷却速度增大,复合材料基体偏析加剧;随复合材料中纤维体积分数增大,基体中偏析减小.     

冷却速率对Al-20％Si合金Si相形貌及性能的影响

使用高精度测温仪、金相显微镜(OM)和扫描电镜(SEM)等手段,研究了冷却速率、过冷度和再辉温度对Al-20%Si合金Si相形貌和性能的影响。结果表明:Al-20%Si合金初生Si的平均尺寸(D)与冷却速率(v)呈幂函数关系D=260.6v^-3/4,而与再辉温度(T_m)则呈线性关系D=0.25T_m-143.12;降低初生Si生长的再辉温度,是控制晶粒长大的关键;铜模的高蓄热系数能持续降低初生Si的形核温度和再辉温度,使初生Si细小;初生Si由小平面生长转变为非小平面生长的临界过冷度为70 K,与理论计算结果(74 K)基本一致;随着冷却速率的增大、过冷度的增加和再辉温度的降低,Al-20%Si合金的凝固组织显著细化,合金的抗拉强度由167 MPa提高到210 MPa,延伸率则由2.14%提高到3.89%。     

凝固速度对镁合金阳极组织与性能的影响

以Mg-Hg-X合金为研究对象,利用金相显微镜、扫描电子显微镜、电化学测试仪等研究了不同铸造凝固速度对镁合金阳极经混合酸侵蚀后显微组织、电化学性能和腐蚀速率的影响.结果表明,Mg-Hg-X合金中Mg、Hg形成的第二相化合物组成随合金铸造凝固速度变化而改变,缓慢凝固主要形成Mg3Hg相,快速凝固主要形成Mg2Hg相;同时随铸造凝固速度加快,Mg-Hg-X合金材料腐蚀速率有所降低,电极电位正移.     

原位自生TiB2/Al-4.5Cu复合材料微观组织和力学性能

采用混合盐反应法制备TiB2含量分别为0%,2%,5%,8%(质量分数,下同)的TiB2/Al-4.5Cu复合材料,T6热处理后,采用XRD,ICP,OM,SEM,EDS等测试手段和室温拉伸实验进行微观组织观察和力学性能测试。XRD和ICP测试证实,合金体系中仅含α-Al,Al2Cu及TiB2,无Al3Ti,Al2B等反应中间产物。OM和SEM发现,基体材料中α-Al平均晶粒尺寸为167.5μm,而在2%,5%,8%的TiB2/Al-4.5Cu中,其平均晶粒尺寸依次为110.4,87.2,75.2μm,晶粒细化效果显著。TEM观察发现,TiB2颗粒主要分布在晶界处,呈四方和六方结构。室温拉伸实验表明,随着TiB2含量的增加,强度、显微硬度值均呈增加趋势,但伸长率不断下降。当加入8%TiB2时,屈服强度、抗拉强度、弹性模量和显微硬度分别达到356 MPa,416 MPa,92.5GPa和96.5HV,但其伸长率从10.3%降低到4.3%。载荷传递强化、细晶强化、位错增殖强化是TiB2/Al-4.5Cu复合材料力学性能得以大幅提升的影响因素,尤其是在位错增殖强化作用下,TiB2颗粒周边致密分布的位错胞、位错环对强度的提升起到了决定性作用。     

Microstructure modification for 2219 Al alloy through ultrasonic treatment and fast cooling

The combined effects of ultrasonic treatment and fast cooling on the bulk hydrogen content, the refinement of α-Al grains and θ-Al₂Cu precipitated phase in the 2219 Al alloy were investigated in this work. Results showed that under the combined effects of ultrasonic treatment and liquid nitrogen cooling, the bulk hydrogen content was dramatically reduced. Metallography and scanning electron microscopy results indicated that both the α-Al grains and θ-Al₂Cu precipitated phase were greatly refined under the combined effects of ultrasonic treatment and liquid nitrogen cooling. Correspondingly, the 2219 Al alloy sample exhibited excellent mechanical properties due to the refinement of α-Al grains and θ-Al₂Cu precipitated phase as well as the low bulk hydrogen content.     

Computer simulation of solidification and microsegregation in presence of particles

A computer simulation was used to study the influence of particles on microsegregation during solidification. Particles in the melt can affect the solidification microstructure by changing the cooling curves, acting as barriers to solute diffusion, reducing the metal volume, affecting the coarsening process, etc. The computer simulation model used in the present work calculates the effect of particles of different thermal properties on the cooling curves and the consequent changes to microsegregation and dendrite arm spacing. The microsegregation calculations are valid for cases where the interparticle spacing is much smaller than the dendrite arm spacing. By using the simulation, it was possible to study various contributing factors in isolation as well as in combination so that the relative significance of each factor could be evaluated. It was observed that the reduction of liquid volume by the presence of the particles was the largest contributing factor to the influence of particles on the solidification microstructure. Thus, the changes in matrix microstructure of cast metal matrix composites depend more on the volume fraction of the reinforcing particles than on the properties of the particles themselves. Irrespective of the thermal properties of the particles, the dendrite arm spacing and microsegregation in the composite matrix was seen to be less than in the unreinforced alloy solidified under the same external conditions.

MST/3405     

Effect of the Presence of SiCp on Dendritic Coherency of Al-Si-Based Alloys During Solidification

In order to explore the effect of the presence of SiC particles on dendritic coherency during solidification of Al-Si based metallic alloys, a factorial fractional two levels experimental design was implemented to allow an identification of the main effects of the particle content, silicon content, grain refinement, and cooling rate on the solid fraction at coherency. This solidification parameter was determined for Al-3wt%Si and Al-7%Si alloys, and Al-3%Si/SiCp and Al-7%Si/SiCp metal matrix composites. The cooling process during solidification was monitored by performing cooling curve measurements at two radial locations within samples poured into cylindrical molds at two cooling rates. The experimental cooling curves were numerically processed by the Fourier thermal analysis method to know the evolution of solid fraction as a function of time. The effect of grain size was included using samples with or without grain size refinement. The grain refinement was obtained by adding predetermined quantities of TiAlB master alloy. It was found that presence of SiC particles affects the coherency point of the metal matrix composites increasing the solid fraction at coherency. However this effect is relatively small when compared to the effect of grain refinement, cooling rate, and Si content on dendritic coherency of experimental probes.     

Influence of cooling rate on interlaminar fracture properties of unidirectional commingled CF/PEEK composites

The influence of cooling rates on the mechanical property profile (transverse flexure properties and modes-I and -II interlaminar fracture toughness) has been investigated for unidirectional commingled CF/PEEK composites. A laboratory hot press with a steel mould was used to process the composites at 400°C for 60 min, at an applied pressure of 1 MPa. Cooling rates from fast (quenching in oil) to slow (hot press cooling) were achieved at ambient pressure. The results indicate that different matrix morphology was found at different cooling conditions, although deconsolidation occurred in the CF/PEEK composites during cooling. When the cooling rate was shifted from slow to fast, consolidation quality of the CF/PEEK composites was improved. The resulting effect of the consolidation quality and cooling rates on the mechanical property profile of commingled CF/PEEK composites is presented. It was found that the effect of the cooling rate on the mechanical property profile of the commingled CF/PEEK composites could not be isolated from the consolidation quality.     

Mg对原位自生TiB2/Al-4.5Cu复合材料微观组织及力学性能的影响

采用Al-K₂TiF₆-KBF₄混合盐原位自生反应法,制备了不同Mg质量分数的3wt% TiB₂/Al-4.5Cu复合材料。采用SEM、TEM、HM硬度测试和室温拉伸等方法研究了Mg含量和多级热处理对3wt% TiB₂/Al-4.5Cu复合材料微观组织和力学性能的影响。微观组织观察发现:Mg质量分数为3wt%时,经过多级热处理后,TiB₂颗粒的团聚现象明显改善,反应生成的TiB₂颗粒平均尺寸约为130 nm,基体内伴随有大量弥散分布的纳米级颗粒,且α-Al的晶粒尺寸也明显减小。力学测试结果表明:多级热处理后,3wt% TiB₂/Al-4.5Cu复合材料的硬度和抗拉强度随Mg含量的增加而提高,但过量的Mg (≥4wt%)会造成TiB₂颗粒细化效果下降。分析表明:Mg的加入能够降低TiB₂/α-Al界面能,减少脆性相Al₃Ti、Al₂B的生成,并通过反应生成的MgAl₂O₄使界面结构变成TiB₂/MgAl₂O₄/α-Al,从而有效抑制了TiB₂的团聚,改善了TiB₂颗粒与Al液界面的润湿性,提高了形核率,进一步细化了α-Al晶粒尺寸。      

电化学浸渗法制备纤维/铜基复合材料

基于电化学浸渗技术(ECI)在室温下制备了连续铜纤维、碳纤维和玻璃纤维增强铜基复合材料。实验结果表明,在本实验工艺条件下可获得致密的纤维/Cu基复合材料,并具有优良的力学性能。复合材料的断口形貌及显微结构的SEM观察表明,纤维与铜基体之间的界面结合良好,纤维不受任何损伤。证实了ECI在室温下快速制备纤维增强金属基复合材料的可行性。     

Numerical Modelling and Experimental Investigation of Microse-gregation in Al-4.45 wt pct Cu: Effect of Dendrite Joining

1.IntroductionNumerical simulation of solute microsegregationhas become increasingly popular over the last severaldecades.The effects of solute back diffusion[1,2],den-drite coarsening[3],tip undercooling[4,5]and variation ofequilibrium data at the solid/liquid(S/L)interface[6~8]on the microsegregation have been investigated in vari-ous segregation models.In these models,dendrites arerepresented in spherical,cylindrical or plate-like geome-tries.During calculation the whole dendrite surface w…     

Effect of Matrix Constitution on Microstructure and Mechanical Properties of Rheocast Metal Matrix Composites

In this study, aluminum-based metallic matrices with varying amounts of copper (I wt.% Cu, 3 wt.% Cu and 4.5 wt.% Cu) were reinforced with SiC particulates using a partial liquid phase casting technique. Microstructural characterization studies conducted on the composite samples revealed an increase in uniformity of distribution of SiC particulates and SiC/Al interfacial integrity and a decrease: in porosity in the metallic matrix with decreasing weight percent of copper. The results of the ageing studies revealed an accelerated ageing kinetics for the Al-1% Cu/SiC composite when compared to Al-3% Cu/SiC and Al-4.5% Cu/SiC samples. Results of ambient temperature mechanical tests demonstrate an increase in 0.2% yield strength and ultimate tensile strength of the composites and a decrease in ductility and strain hardening rate with an increasing weight percent of copper in the metallic matrix. Fracture studies revealed the presence of interfacial debonding, particulate breakage and cracks in the matrix of tensile specimens. The results of microstructural characterization, mechanical testing and fractography were finally rationalized in terms of the effect of variation in weight percent of copper in the metallic matrix.     

碳纤维-AlN/聚醚醚酮复合材料的制备与性能

以聚醚醚酮(PEEK)为基体树脂、碳纤维(CF)和氮化铝(AlN)为填料,通过模压成型的方法制备了抗静电耐热型CF-AlN/PEEK复合材料。采用高阻计、导热系数测定仪、热失重、差示扫描量热仪和SEM研究了CF-AlN/PEEK复合材料的抗静电性能、热性能、力学性能以及降温速率对复合材料性能的影响,并探讨了后期热处理对力学性能的影响。结果表明:当CF和AlN的质量分数均为10%时,CF-AlN/PEEK复合材料的性能较优,其表面电阻率达到108 Ω,比PEEK的表面电阻率提高了6个数量级;导热系数为0.418 W·(m·K)-1,初始分解温度高达573℃;拉伸强度提高了40.4%;降温速率越低,复合材料的熔点越高;后期热处理会影响CF-AlN/PEEK复合材料的力学性能,在270℃下热处理2 h,其拉伸强度可达146 MPa,表明在生产过程中,加工温度是影响复合材料性能的因素之一。