漂珠/AZ91D复合材料微观组织与性能的研究

采用搅拌铸造法,向镁合金熔体中添加漂珠,制备了漂珠/AZ91D复合材料,研究了该复合材料微观组织的均匀性、相组成、力学性能和阻尼性能。结果表明,漂珠在基体中分布均匀,无偏聚现象。在复合材料制备过程中,漂珠与镁合金熔体发生反应并被填充,使得复合材料中有Mg₂Si和MgO相生成。与基体合金相比,复合材料的力学性能和阻尼性能均得到明显提高。复合材料的断裂是以解理断裂为主的脆性断裂,在断裂过程中漂珠壁被撕裂。复合材料的阻尼机制主要是位错阻尼和界面阻尼。     

A Novel Method to Fabricate CNT/Mg–6Zn Composites with High Strengthening Efficiency

A novel method was developed to fabricate carbon nanotubes （CNTs）-reinforced Mg matrix composites. The method consists of two steps： CNTs pre-dispersion by ball-milling and the ultrasonic melt processing. Mechanical ball- milling effectively pre-dispersed CNTs on Zn flakes with suitable rotational speed and ball-milling time. Serious CNT entanglements were dispersed by the ball-milling. However, ball-milling for a long time at high speed would damage the morphology of CNTs. The ultrasonic overcame the poor wettability between Mg melt and CNTs and then dispersed pre-dispersed CNTs in the Mg melt. CNTs were distributed well in the composites and maintained integrated structure. CNTs significantly improved the mechanical properties of the matrix. The strengthening efficiency reached to 37.1, which proves the superiority of this novel method. Besides grain refinement, load transfer may make a great contribution to the improvement of the strength for the composites.     

Processing,Microstructure and Mechanical Properties of Ti6Al4V Particles-Reinforced Mg Matrix Composites

Novel Ti6Al4V particles-reinforced AZ91 Mg matrix composites were successfully fabricated by stir casting method. The stirring time in semisolid condition directly affected the particle distribution and the quality of the ingots.Furthermore, the optimal speed of the heating and the liquid stirring could overcome particle settlement caused by the density difference between the matrix and the particles. Ti6Al4V particles distributed uniformly in the composites with different particle contents. The average grain size decreased with the increase in the particle contents. The Ti6Al4V particles bonded pretty well with the alloy matrix. In addition, there were some interfacial reactions in the composites.There were rod-like Al_3Ti phases at the interface. The precipitates extended from the particle surface to the matrix, and they might improve the interfacial bonding strength. The ultimate tensile strength, yield strength and elastic modulus were enhanced as the particle contents increased, and the elongation was much better than that of the same matrix material reinforced with SiC particles. Thus, the novel composites exhibit better comprehensive mechanical properties.     

Be、RE对AZ91D阻燃性、组织及力学性能的影响

研究了Be的加入量对镁合金AZ91D起燃温度的影响,以及Be、RE对AZ91D显微组织与力学性能的影响.结果表明,含0.3％Be的AZ91D的起燃温度提高近300℃,Be的加入促进Mg17Al12相以离异共晶方式析出,降低了AZ91D的拉伸性能.加入1.0％RE可抑制Mg17Al12相的析出,从而强化了基体,Al4 RE相可阻止裂纹的形成与扩展,增大试验合金的断裂抗力,使抗拉强度显著提高.固溶处理后拉伸性能得到了进一步提高.     

n-SiC_p/AZ91D镁基复合材料高温力学性能

采用机械搅拌和高能超声处理法制备了n-SiCp/AZ91D镁基复合材料,测试了复合材料的室温及高温力学性能。结果表明,n-SiCp的加入能显著提高复合材料的高温力学性能,当n-SiCp加入量为1.5%时,复合材料的抗拉强度和伸长率都达到最大值。随着温度的升高,复合材料的强度降低,伸长率增加。断口形貌观察表明,复合材料的断裂方式由室温下的准解理断裂转变为高温下的韧性断裂。     

碳纳米管预制块铸造法制备CNTs/AZ91复合材料研究

在氢气保护下,采用碳纳米管预制块铸造法制备了碳纳米管/AZ9I镁基复合材料.观察和分析了复合材料的微观组织,测试了其室温力学性能,并利用扫描电子显微镜(SEM)和能谱分析(SED)对复合材料拉伸断口形貌进行了观察和分析.研究结果表明:该方法能有效地将碳纳米管添加到镁合金熔体中并且均匀分散;随着碳纳米管的加入,复合材料的晶粒组织得到不断的细化,综合力学性能得到明显提高.     

TiC含量对高温钛基复合材料组织与性能的影响

通过真空非自耗熔炼工艺制备了不同TiC含量(1,2.5,5,7.5,10,15vol.%)的近α高温钛合金基复合材料。采用X射线衍射仪(XRD)、金相显微镜(OM)、扫描电镜(SEM)和万能材料试验机,系统研究了TiC_p含量对近α高温钛合金基复合材料显微组织和力学性能的影响规律。研究结果表明,可以利用Ti与C之间的原位反应制备TiC/Ti复合材料,随着TiC含量的升高,TiC的形态逐渐由长条状向等轴状、枝晶状发展,其不同的形态主要是由其凝固路径决定的。室温压缩性能表明,随着TiC含量的升高,抗压强度和屈服强度明显升高,但达到一定值后强度有不同程度的降低,而压缩率随着TiC含量的升高明显降低。     

混合稀土对压铸AZ91D合金的组织及力学性能的影响

研究了不同添加量的混合稀土对压铸AZ91D合金的组织和力学性能的影响。添加混合稀土后,常温力学性能没有明显改善。在100℃时,混合稀土含量为0.4%的压铸AZ91D合金的力学性能与不含混合稀土的试样几乎相等。在170℃时,混合稀土含量为0.4%的压铸AZ91D合金的抗拉强度、屈服强度及伸长率分别为206MPa、142MPa、26%,比不含混合稀土的压铸AZ91D试样的力学性能分别提高15.7%、10%及30%。这是因为添加适量的混合稀土后,形成热稳定性较高的强化相,增加了位错滑移阻力并阻碍裂纹扩展,镁基体中稀土元素起到固溶强化作用,从而提高镁合金的高温抗拉强度。     

原位合成TiC/AZ91复合材料力学性能的研究

采用重熔稀释法原位制备了不同质量分数的TiC颗粒增强的镁基复合材料,并对复合材料进行了力学性能测试。结果表明,原位合成的镁基复合材料的强度相比基体合金有了明显提高,塑性稍微降低。镁基复合材料强度的增加主要是因为位错强化、弥散强化和细晶强化协调作用的结果。     

纳米碳管增强镁基材料的复合工艺及性能研究

采用正交试验方法研究了碳纳米管加入量、复合温度、搅拌时间等工艺参数对用铸造方法制备纳米碳管增强镁基复合材料过程的影响,并探讨了这些工艺参数对复合材料力学性能和显微组织的作用.试验结果表明:碳纳米管(CNTs)能明显细化复合材料的晶粒组织,提高复合材料的抗拉强度、伸长率.在3个工艺参数中,CNTs对材料的力学性能影响最大,其含量约为1%时对力学性能最为有利;其次是加热温度,温度取低值(680 ℃)较好;搅拌时间在3 min时,其综合性能较好.影响材料拉伸强度的3个因素最优组合为A 2B 1C 3,影响伸长率的3个因素的最优组合为A 2B 1C 3.     

Strengthening Mechanism and Microstructure of Deformable Ti Particles Reinforced AZ91 Composite

In this study, the deformable titanium (Ti) particles reinforced AZ91 composite was successfully prepared by powder metallurgy and subsequent extrusion. The mechanical properties and microstructural evolution of pure AZ91 and 5Ti/AZ91 composite were studied. The yield strength, ultimate tensile strength, and elongation of 5Ti/AZ91 composite are measured to be 212 MPa, 323 MPa, and 10.1%, respectively. Microstructure analysis revealed that Ti particles are elongated along the extrusion direction, forming a discontinuous strip Ti particles, fine precipitated Mg₁₇Al₁₂ phase inhibits dynamic recrystallization (DRX) behavior through Zener pinning effect and hinders the growth of matrix grains, resulting in refiner grains of 5Ti/AZ91 composite. Heterogeneous deformed Ti particles and magnesium (Mg) matrix to generate additional heterogeneous deformation-induced (HDI) strengthening. Heterogeneous deformation-induced strengthening mainly contributed to the increment of yield strength for 5Ti/AZ91 composite.     

碳纤维增强AZ91D复合材料微观组织

采用压力浸渗法制备碳纤维增强AZ91D镁基复合材料,利用扫描电子显微镜、能谱分析仪、透射电子显微镜等分析测试手段对其微观组织进行研究.结果表明,基体镁合金中的Al元素在界面处发生偏聚.随着纤维石墨化程度提高,界面反应程度降低,界面反应物Al4C3的量逐渐减少.由于受到复合材料制备过程中产生的热应力以及制备压力的共同作用,致使基体镁合金发生塑性变形,在近界面区形成大量的位错.在远离界面的基体合金中存在大量块状和杆状的a-Mg17Al12析出相.     

TiC/Ti层状复合材料组织与力学性能研究

为了平衡钛基复合材料（titanium matrix composites, TMCs）的强度和延展性,通过电泳沉积将氧化石墨烯（graphene oxides, GOs）沉积到Ti箔表面,然后进行放电等离子烧结（spark plasma sintering, SPS）制备了具有层状结构的原位TiC/Ti复合材料,并对复合材料进行冷轧和退火处理从而进一步优化复合材料的综合力学性能。结果表明,烧结过程中,Ti箔表面的GOs与Ti基体反应形成了原位TiC,从而形成了TiC/Ti层状复合材料,随着沉积时间的增加,分布在Ti层之间的TiC的含量增加;复合材料经过冷轧和退火后,退火态材料的晶粒为等轴晶,且TiC仍然保持层状分布特征。沉积时间120 s时,烧结态材料的抗拉强度（UTS）为555 MPa,伸长率（δ）为15%;退火态材料的抗拉强度为568 MPa,伸长率为27%,相比于烧结态材料,退火态材料达到了较好的强塑性匹配。此外,基于微观组织及断裂行为的分析对复合材料的强韧化机制进行了讨论。     

CNTs/AZ91D镁基纳米复合材料的热处理及其力学性能

采用高能超声分散技术和金属型重力铸造工艺制备了CNTs/AZ91D镁基纳米复合材料,并对复合材料进行了固溶T4热处理和固溶时效T6热处理。T4态1.0CNTs/AZ91D复合材料的抗拉强度、伸长率分别为285 MPa、17.3%,与铸态复合材料的抗拉强度(196MPa)和伸长率(4.1%)相比,分别提高了45%、322%。T6态的抗拉强度进一步提高到296MPa,特别是屈服强度显著提高到155MPa,伸长率有所降低,但仍有5.5%。利用OM、SEM、TEM观察1.0CNTs/AZ91D复合材料的显微组织。结果表明,碳纳米管具有细化晶粒、促进滑移和孪生、载荷转移等作用,从而能够明显提高CNTs/AZ91D复合材料的综合力学性能。     

Influences of Asymmetric Reduction Rolling on the Microstructure and Mechanical Properties of AZ91

The influence of asymmetric reduction rolling(ARR) on the microstructure, texture and mechanical properties of AZ91 was investigated. The microstructural characteristics of the AZ91 sheet processed by symmetric rolling(SR) were the twins, intersection of twins and dynamic recrystalization(DRX) grains around the coarse grains and within the twins.However, the amount of twins and DRX grains in ARRed AZ91 was much smaller than that in SRed AZ91. The SRed AZ91 after annealing exhibited fine DRX grains and some coarse grains with a size of * 100 lm. The grains in ARRed AZ91 after annealing were much finer and more homogeneous than those in SRed AZ91 after annealing. The intensity of basal texture of ARRed AZ91 after annealing was lower than that of SRed AZ91 rolling after annealing. The average Schmid factor of ARRed AZ91 is 0.34, which is higher than that of SRed AZ91. The yield strength and ultimate tensile strength of the ARRed AZ91 sheet were increased to 16.1% and 31.8% compared to SRed AZ91 sheet, from 155 to180 MPa, and from 220 to 290 MPa, respectively. The improvement of mechanical properties in ARRed AZ91 after annealing was attributed to much finer, more homogeneous DRX grains and weaker basal texture.     

碳纳米管-银复合材料力学性能研究

采用粉末冶金方法制备碳纳米管-银复合材料，研究了碳纳米管的含量对碳纳米管-银复合材料的硬度、抗弯强度影响。实验表明：当碳纳米管的含量小于11％时，复合材料的密度、硬度较好，碳纳米管起到了增强作用；当碳纳米管的含量大于11％时，由于碳纳米管的团聚，导致复合材料密度、硬度迅速下降；由于碳纳米管和银的弱界面结合，以及碳纳米管在拉应力条件下载荷传递的效力比在压应力时低，使得碳纳米管对复合材料抗弯强度的增加不明显。     

Microstructure and Mechanical Properties of TiC-Reinforced Al-Mg-Sc-Zr Composites Additively Manufactured by Laser Direct Energy Deposition

In order to refine the microstructure and improve the performance of direct energy deposited (DED) additively manufactured Al-Mg-Sc-Zr alloy, TiC-modified Al-Mg-Sc-Zr composites were prepared by DED and the effect of TiC content on the microstructure and performance was studied. In the absence of TiC particle, the microstructure of Al-Mg-Sc-Zr alloy prepared by DED consisted of fine grains with average size of 8.36 μm, and well-dispersed nano-Al₃(Sc,Zr) particles inside the grains and Mg₂Si phase along the grain boundaries. With the addition of 1 wt% TiC, the microstructure of TiC/Al-Mg-Sc-Zr prepared by DED became finer apparently compared with that without TiC; while the further increase of TiC content to 3 wt%, the microstructure of TiC/Al-Mg-Sc-Zr prepared by DED became coarser with appearance of a new kind of needle-like (Ti,Zr)₅Si₃ phase. Also, the addition of TiC decreased the porosity of Al-Mg-Sc-Zr prepared by DED. Simultaneously, after the addition of TiC, the tensile strength increased from 283.25 MPa to 344.98-361.51 MPa, and the elongation increased from 3.61% to 9.58-14.10%. The potential mechanism of the microstructure evolution and strength improvement was discussed. This research will provide new insights into the available metal matrix composites by laser additive manufacturing (LAM).     

高能球磨结合粉末冶金法制备碳纳米管增强7055Al复合材料的微观组织和力学性能

采用高能球磨结合粉末冶金工艺制备了碳纳米管(CNT)含量(体积分数)分别为0、1%和3%的CNT/7055Al复合材料。采用OM、SEM、TEM以及拉伸实验等方法研究了CNT/7055Al复合材料的CNT分布、晶粒结构、近界面结构及力学性能,分析了复合材料的强化机制和各向异性。结果表明,CNT/7055Al复合材料为无CNT的粗晶区与富集CNT的超细晶区组成的双模态晶粒结构;CNT在Al基体的超细晶区中分散良好,CNT-Al界面干净清洁,界面反应产物少;3%CNT/7055Al复合材料沿挤压方向的抗拉强度达到816 MPa,但延伸率仅为0.5%。细晶强化和Orowan强化是CNT/7055Al复合材料主要的强化机制。由于CNT沿不同方向的增强效率不同以及粗晶条带组织的存在,复合材料表现出比基体合金更强烈的各向异性,在垂直挤压方向的拉伸性能要弱于沿挤压方向的拉伸性能。