SiCP/AZ91复合材料的显微组织、力学性能及强化机制

通过搅拌铸造工艺制备出SiC_P体积分数分别为2%、5%、10%和15%的4种5 μm SiC_P/镁合金（AZ91）复合材料。对5 μm SiC_P/AZ91进行了固溶、锻造和热挤压。通过与AZ91对比,研究了SiC_P对AZ91基体热变形后显微组织和力学性能的影响规律。结果表明：SiC_P/AZ91热变形后的晶粒尺寸取决于SiC_P的体积分数。SiC_P的体积分数由0%增加到10%时,SiC_P/AZ91热变形后的平均晶粒尺寸减小;当SiC_P颗粒继续增加到体积分数为15%时,平均晶粒尺寸反而增大。SiC_P的加入能显著提高AZ91的屈服强度和弹性模量,并随颗粒体积分数的增加而增大。SiC_P对AZ91基体的强化作用主要源于位错强化、细晶强化和载荷传递作用,其中,细晶强化对屈服强度的贡献最大。     

挤压包覆轧制对SiCP增强镁合金(AZ91)复合板显微组织和力学性能的影响

通过热挤压复合的方式将AZ91合金引入至SiC_P增强镁合金（AZ91）（SiC_P/AZ91）复合材料中,制备出厚度为2 mm的AZ91-（SiC_P/AZ91）复合板,研究了热轧对其显微组织和力学性能的影响规律。研究结果表明:AZ91的引入显著提高了SiC_P/AZ91的轧制成形能力。与AZ91层相比,SiC_P/AZ91层内晶粒尺寸小,硬度高。随轧制压下量的增加,AZ91-（SiC_P/AZ91）复合板晶粒尺寸变大,析出相数量减少且尺寸增大,导致硬度呈现下降的趋势。与挤压态AZ91-（SiC_P/AZ91）复合板相比,当压下量为50%时,轧制态AZ91-（SiC_P/AZ91）复合板屈服强度由272 MPa提高至341 MPa,抗拉强度由353 MPa提高至404 MPa。在拉伸过程中,因SiC_P与基体界面脱黏导致裂纹优先在SiC_P/AZ91层内萌生和扩展,AZ91层对微裂纹扩展具有一定的阻碍作用。      

短切碳纤维/AZ91D镁合金复合材料高温变形动态再结晶行为

在变形温度为340~400℃、应变速率为0.001~0.1 s^-1、最大真应变为0.7的条件下,采用等温压缩实验研究了短切碳纤维（CF_s）/AZ91D复合材料和AZ91D镁合金的动态再结晶行为。结果表明：CF_s/AZ91D复合材料和AZ91D镁合金在高温压缩过程中均发生了显著的动态再结晶;CF_s极大地促进了AZ91D基体的动态再结晶过程,减小了动态再结晶临界应变并细化了再结晶晶粒组织;AZ91D镁合金动态再结晶体积分数随应变量增加表现为典型的"S"型变化曲线,而CF_s/AZ91D复合材料则呈现出快速增长-缓慢增长-趋于平稳的非线性变化规律。根据实验结果分别建立了CF_s/AZ91D复合材料和AZ91D镁合金的动态再结晶临界应变模型和动力学模型,在此基础上分析了二者高温变形动态再结晶行为的差异。     

SiC_P/AZ91复合材料的显微组织、力学性能及强化机制

通过搅拌铸造工艺制备出SiCP体积分数分别为2%、5%、10%和15%的4种5μm SiCP/镁合金(AZ91)复合材料。对5μm SiCP/AZ91进行了固溶、锻造和热挤压。通过与AZ91对比,研究了SiCP对AZ91基体热变形后显微组织和力学性能的影响规律。结果表明:SiCP/AZ91热变形后的晶粒尺寸取决于SiCP的体积分数。SiCP的体积分数由0%增加到10%时,SiCP/AZ91热变形后的平均晶粒尺寸减小;当SiCP颗粒继续增加到体积分数为15%时,平均晶粒尺寸反而增大。SiCP的加入能显著提高AZ91的屈服强度和弹性模量,并随颗粒体积分数的增加而增大。SiCP对AZ91基体的强化作用主要源于位错强化、细晶强化和载荷传递作用,其中,细晶强化对屈服强度的贡献最大。     

粉煤灰漂珠粒径对粉煤灰漂珠/AZ91D镁合金复合材料阻尼性能的影响

通过搅拌铸造法向半固态AZ91D镁合金中添加粉煤灰漂珠（FAC）制备了FAC/AZ91D镁合金复合材料,研究了FAC粒径对该复合材料阻尼性能的影响。结果表明:FAC/AZ91D镁合金复合材料的阻尼性能明显优于基体材料,在FAC含量相同时,FAC的粒径越大,其阻尼性能越好。室温下FAC对提高FAC/AZ91D镁合金复合材料的阻尼性能起重要作用,FAC附近的基体产生了高密度的位错,形成了塑性区。室温下FAC粒径越大,在其附近产生的塑性区越大,阻尼性能越好。随温度的升高,FAC/AZ91D镁合金复合材料的阻尼性能迅速提高。位错、晶界以及FAC和基体之间的界面运动是提高阻尼性能的关键。      

热挤压对双尺度SiCp/AZ91镁基复合材料显微组织与拉伸性能的影响

目的 细化SiCp/AZ91镁基复合材料基体晶粒,提高其拉伸强度.方法 基于半固态搅拌铸造的方法制备出双尺度SiCp/AZ91镁基复合材料(标记为M-9+S-1).在不同温度下对M-9+S-1进行慢速挤压,研究挤压温度对其显微组织和力学性能的影响规律.结果 SiCp一方面能够促进DRX形核,使M-9+S-1复合材料基体晶粒得以显著细化;另一方面,能够促进大量细小Mg17Al12相的动态析出,显著提升热挤压后的性能.结论 M-9+S-1经250℃热挤压后,基于动态析出和动态再结晶的双重作用,拉伸性能得以显著提升,其中,屈服强度和抗拉强度可分别提升至～342 MPa和～380 MPa.     

挤压复合AZ91-(SiC_(P)/AZ91)复合板材显微组织和力学性能EI北大核心

在300,350,400℃下成功通过挤压复合法制备多层AZ91-(SiC_(P)/AZ91)复合板,探究AZ91-(SiC_(P)/AZ91)复合板中SiC_(P)/AZ91复合材料层和AZ91层的显微组织演变、界面的演化机制和力学性能变化规律。结果表明:热挤压复合中,AZ91-(SiC_(P)/AZ91)多层复合板中合金层发生完全动态再结晶,晶粒细化,合金组织随挤压温度的升高更均匀,而且外层合金层比内层合金层晶粒尺寸略大;SiC_(P)/AZ91复合材料层同样发生完全动态再结晶,晶粒尺寸小于合金层,随着挤压温度的升高,SiC_(P)的分布更加均匀;不同挤压温度下AZ91-(SiC_(P)/AZ91)复合板合金层与复合材料层界面均未出现明显的分层以及开裂现象;AZ91-(SiC_(P)/AZ91)复合板的室温力学强度位于AZ91合金与SiC_(P)/AZ91复合材料之间,SiC_(P)/AZ91层中SiC_(P)与基体界面脱粘是导致复合板材失效的主要原因。     

镍涂层短碳纤维增强AZ91D镁基复合材料的界面特征和阻尼性能

使用表面化学镀镍的短碳纤维为增强体、AZ91D粉为基体金属,用粉末冶金法和热挤压工艺制备镁基复合材料,用SEM、TEM-EDS、拉伸和动态热机械分析(DMA)等手段表征其微观形貌、界面结构、力学性能和阻尼性能,研究了金属镍涂层短碳纤维对AZ91D镁基复合材料的界面和阻尼性能的影响。结果表明,碳纤维在复合材料中分布均匀,沿着挤压方向定向排列;镍涂层改善了碳纤维与AZ91D基体之间的润湿性;不同频率的应变谱和G-L特征线都表明:复合材料的阻尼机制,除了位错之外还有其他机制;随着应变频率的提高复合材料的阻尼机制由以界面滑移为主转变为以位错为主。随着温度的升高涂层碳纤维增强镁基复合材料的阻尼容量增大,在250~300℃出现一个阻尼峰。随着频率的提高阻尼峰值的温度移向高温,表现出热激活弛豫过程的特征,根据Arrhenius公式计算出其热激活能(H)为3.448 e V。     

SiCp/AZ91复合材料大口径管材的热挤压成形研究

目的 解决镁基复合材料大口径管材成形加工困难的问题。方法 通过搅拌铸造技术制备的SiC颗粒增强AZ91镁基复合材料百公斤级铸锭坯料,开展了大口径镁基复合材料管材的热挤压成形工艺优化,分析复合材料变形过程中组织与力学性能演变规律,并揭示了其微观机制。结果 复合材料管材最佳热挤压工艺参数为：挤压温度为400 ℃,挤压速度为1 mm/s,在最佳的工艺下成功成形出外径260 mm和130 mm的SiC颗粒增强AZ91镁基复合材料挤压管材,复合材料挤压管材的弹性模量、屈服强度、抗拉强度、伸长率分别可以达到72 GPa,302 MPa,356 MPa,1.2%。结论 对温度、挤压比、挤压速度等工艺参数的优化,以及利用SiC颗粒对再结晶行为的促进作用,是制备出大尺寸复合材料管材的关键。     

放电等离子体烧结制备Mg85Zn6Y9颗粒增强Mg-9Al-1Zn复合材料组织与力学性能

采用高能球磨法和放电等离子体烧结（SPS）技术,以包含100%长周期堆垛有序结构（LPSO）相Mg₈₅Zn₆Y₉镁合金为原料,通过将其球磨成纳米晶颗粒后与Mg-9Al-1Zn（AZ91）镁合金雾化颗粒进行机械混合,并在350℃烧结温度下成功制备出不同质量分数（0~30wt%）的LPSO相Mg₈₅Zn₆Y₉颗粒增强AZ91复合材料（Mg₈₅Zn₆Y₉/AZ91）。采用光学显微镜（OM）、SEM及TEM对Mg₈₅Zn₆Y₉/AZ91复合材料的微观组织结构进行表征;采用XRD分析其固溶处理前后的相转变;与此同时对复合材料进行显微硬度与压缩试验,综合研究其微观组织与力学性能的关系。相关结果表明,Mg₈₅Zn₆Y₉颗粒经3 h高能球磨后颗粒尺寸显著减小,硬度随晶粒细化而提升。Mg₈₅Zn₆Y₉增强颗粒主要分布在AZ91基体颗粒边界处,随着Mg₈₅Zn₆Y₉质量分数的增加,增强相颗粒有相互结合成连续网格状趋势。增强颗粒与基体界面处未见明显过渡层,基体界面处的β相经400℃×24 h固溶处理后进入基体,部分增强颗粒亦转变为Mg相。本实验条件下制备的最佳性能的20wt% Mg₈₅Zn₆Y₉/AZ91复合材料经固溶处理后的室温屈服强度从200 MPa转变为230 MPa,屈服强度均较未添加Mg₈₅Zn₆Y₉的AZ91镁合金有较大的提高。     

Influences of extrusion parameters on microstructure and mechanical properties of particulate reinforced magnesium matrix composites

SiCp/AZ91 composites fabricated by stir casting were extruded at different extrusion temperatures and ratios. Extrusion reduced the necklace-type particle distribution and improved particle distribution of the composites. As extrusion temperatures and ratios increased, particle distribution was improved, and the grain sizes of matrix increased. The mechanical properties of the composites were improved with the increase of extrusion temperatures and ratios. The microstructure evolution of matrix was not the main influential factor of the mechanical properties of the composites. The particle evolution, which included particle redistribution and particle cracking induced by extrusion, significantly affected the mechanical properties of the extruded composites.     

Fabrication,microstructures, and tensile properties of magnesium alloy AZ91/SiCp composites produced by powder metallurgy

Abstract

The tensile properties and microstructural evolution of hot extruded AZ91 magnesium alloy with and without reinforcement of SiC particles have been investigated in terms of extrusion parameters, such as extrusion ratio and extrusion temperature. Also, the effect of SiC particles on the grain size of the matrix in the composites was evaluated using the Hall-Petch equation. The AZ91 magnesium alloy powders prepared by wet attrition milling from magnesium machined chips were hot pressed with and without SiC particles, hot extruded, and then solution treated. Microstructural observation revealed that both the composites and the magnesium alloy have fine equiaxed grains due to the dynamic recrystallisation during hot extrusion. The tensile strength of both materials increased with increasing extrusion ratio, and the strengths of the composites were higher than that of the magnesium alloy without reinforcement. It was found that the tensile strength of both the materials decreased after solution treatment, and the decrease in tensile strength of the composites was considerably smaller than that of the magnesium alloy. From analyses of the microstructures and the mechanical properties, combined with examination of the H all–Petch relationship, the refinement of the matrix was primarily responsible for the improvement in the yield strength of the composites. The grain growth of the matrix was inhibited by the introduction of the SiC particles.     

碳纤维表面改性增强Fe3Al-Al2O3复合材料的制备及组织性能

采用溶胶-凝胶分散和热压烧结制备了短切碳纤维（CF_s）/Fe₃Al-Al₂O₃复合材料。分别通过电化学镀Cu和化学气相沉积SiC对CF_s表面修饰和改性,研究了Cu镀层和SiC涂层对CF_s/Fe₃Al-Al₂O₃复合材料显微组织、相组成、力学性能及断裂行为的影响。结果表明,未修饰的CF_s在Fe₃Al-Al₂O₃基体中受到严重侵蚀,CF_s/Fe₃Al-Al₂O₃复合材料致密度低,抗弯强度仅为239.0 MPa,与Fe₃Al-Al₂O₃强度相当;表面镀Cu可有效保护CF_s不被侵蚀,同时提高了CF_s/Fe₃Al-Al₂O₃复合材料的烧结致密性和界面结合强度,从而明显提高了复合材料的断裂强度,但断裂过程中纤维拔出较短;CF_s表面沉积SiC的CF_s/Fe₃Al-Al₂O₃复合材料组织均匀致密,表面涂层完整,且与纤维及基体之间结合力相当,断裂过程中,涂层既可随纤维一起拔出基体,也可与CF_s分离而留在基体之中,SiC涂层与纤维及基体之间的弱相互作用很大程度上促进了纤维脱黏和拔出,从而促进CF_s/Fe₃Al-Al₂O₃复合材料韧化所需的渐进破坏机制。      

热压烧结镀Cr碳纤维/Cu复合材料的制备及热性能

采用热压法将拥有超高导热率和负热膨胀系数（CTE）的中间相沥青基短碳纤维（CF_s）与Cu复合,并利用化学气相沉积技术对CF_s镀Cr以改善其与Cu的结合状况,研究了所制备的镀Cr CF_s/Cu复合材料的显微结构与热性能。结果表明：在制备中Cr层的大部分与CF_s表层的C反应形成连续、均匀的界面薄层Cr₇C₃,少量的扩散于Cu基体中,使CF_s与Cu之间的界面由结合极差的机械结合转化成良好的冶金结合,有效提升了复合材料的热性能。CF_s含量为40vol%~55vol%时,镀Cr CF_s/Cu复合材料致密度高于97.5%,平面方向上的热导率达393~419 W（mK）^-1,平面方向的CTE在5.1×10^-6~8.4×10^-6 K^-1之间。高的热导率、低的CTE以及优良的可加工性能使其成为极有潜力的电子封装材料。     

Microstructures and mechanical properties of ultrafine-grained Ti/AZ31 magnesium matrix composite prepared by powder metallurgy

The microstructure of ultrafine grain for magnesium alloys can result in drastic enhancement in their room temperature strength, but the issue of low strength at elevated temperature becomes more serious as well due to grain boundary slide. Here ultrafine-grained Ti/AZ31 magnesium matrix composites with high strength at both room and elevated temperature were prepared by vacuum hot pressing and subsequent hot extrusion. The microstructure of the composite samples before and after consolidation processing was characterized, and the mechanical properties of the as-consolidated bulk samples were measured at room and elevated temperatures. The results indicate that after extrusion ultrafine-grained magnesium alloys were obtained and Ti particulates with particulate size of ～310?nm disperse in Mg matrix. The magnesium grain of AZ31-15at.%Ti grows from 66?nm to 800?nm. Meanwhile, the relative densities of Ti/AZ31 composites are higher than 99%. The yield strength (YS) of extruded AZ31-15at.%Ti composite at room temperature is 341?MPa, being 2.4 times higher than original AZ31 alloy. Theoretical estimation shows that remarkably enhanced room-temperature mechanical strength attributes to grain boundary strengthening with the contribution ratio of 74%. In addition, the peak stress of extruded AZ31-15at.%Ti composite at 573?K is 82?MPa and ultrafine Ti dispersions are responsible for the enhanced strength.     

热挤压AZ91D镁合金边角料组织和性能的研究

采用热挤压工艺直接热挤出AZ91D镁合金边角料,研究挤压温度对挤压成形镁合金组织和性能的影响,并讨论其断裂行为.结果表明:在450℃热挤压时,晶粒尺寸均匀,组织中已不存在原始边角料之间未打碎的结合面,边角料之间结合较好;在350～450℃之间热挤出时,AZ91D镁合金随挤压温度的升高,抗拉强度和延伸率均增加,当挤压温度...     

EFFECT OF EXTRUSION PARAMETERS ON STRUCTURE AND PROPERTIES OF 2124 ALUMINUM ALLOY MATRIX COMPOSITES

Discontinuously reinforced aluminum matrix composites (DRA) have been attracting attention because of their amenability to undergo deformation processing by conventional metalworking techniques. Extrusion is used in processing of DRA composites for consolidation, redistribution of reinforcements, and shape forming. The important parameters that control the extrusion process are temperature and strain rate, which is a function of several equipment/extrusion parameters. Vacuum hot-pressed (VHP) 2124 Al/30 SiC_p composite billets were extruded at different ram speeds (1, 10, 100 mm sec^-1) and using different extrusion ratios (4:1, 10:1, and 20:1). The extruded samples were studied for their integrity, microstructure, and mechanical properties. The integrity of the extruded composite rod was very good at minimum extrusion speed of 1 mm sec^-1, whereas 100 mm sec^-1 extrusion speed resulted in extensive fir tree cracking. Extrusion of VHP billets, with necklace structure, resulted in elongated alternate stringers of matrix and SiC_p in the extrusion direction. Matrix stringer width and aspect ratio were found to vary with extrusion ratio. Because of the microstructural refinement, both the strength and ductility of the metal matrix composites (MMCs) were improved. Microhardness of the matrix stringers was found to be a function (power relation) of their width, irrespective of the location and extrusion ratio.