等通道角变形对搅拌铸造SiC_P/AZ91复合材料显微组织与室温性能的影响

采用搅拌铸造法成功制备了SiC_P/Mg(AZ91)复合材料并对铸态复合材料进行了等通道角挤压变形(Equal channel angular pressing,ECAP)。结果表明,搅拌铸造态SiC_P/AZ91复合材料的基体组织致密,颗粒与基体结合良好,没有出现宏观团聚;SiC_P大部分聚集在晶界附近区域并呈"项链状"分布。ECAP变形可以有效地消除铸态SiC_P/AZ91复合材料中的SiC_P"项链状"分布,并且随着ECAP道次的增加,SiC_P分布更加均匀;在ECAP过程中,SiC_P发生了一定断裂但并不明显。SiC_P/AZ91复合材料基体晶粒随着变形道次的提高而逐渐细化。基体晶粒细化以及SiC_P分布均匀化是SiC_P/AZ91复合材料屈服强度和抗拉强度随着道次提升而逐渐增加的主要原因。     

挤压对AZ91铸造镁合金力学性能的影响

对挤压变形前后的AZ91镁合金进行了微观组织和力学性能研究.结果表明:挤压成形后合金的抗拉强度和塑性均得到提高;孪晶的产生,导致挤压合金室温压缩的应力-应变曲线上有屈服平台出现;晶粒尺寸强烈影响合金的强度.室温时,挤压合金的流变强度较铸态的高,而高温压缩的强度则较铸态的低.     

搅拌铸造法制备短碳纤维/AZ91复合材料的组织与性能

采用搅拌铸造法制备了不同体积分数（10vol%、15vol%、20vol%）的短碳纤维增强镁基（CF_s/AZ91）复合材料,并选取了三个挤压比和两个挤压温度对其进行热挤压变形,采用光学显微镜（OM）、SEM和TEM对CF_s/AZ91复合材料的显微组织进行了观察,并测试其室温力学性能及阻尼性能。研究结果表明,热挤压能够有效降低CF_s/AZ91复合材料气孔率;在热挤压过程中,纤维沿挤压方向定向排列,同时基体发生动态再结晶。随着挤压温度及挤压比的增大,晶粒呈现等轴状,组织更加均匀。CF_s/AZ91复合材料经过挤压后,其力学性能得到提高,屈服强度和抗拉强度随挤压比和CF_s体积分数的增大而增大,然而CF_s纤维在热挤压后发生明显断裂,限制了挤压态复合材料强度的进一步提升。低温低挤压比条件下,CF_s/AZ91复合材料具有较好的阻尼性能,随着挤压比及挤压温度的升高,CF_s/AZ91复合材料室温及高温阻尼性能均有所降低。      

SiC晶须增强SiCf/SiC复合材料的力学性能

以连续SiC纤维为增强体,采用前驱体浸渍裂解工艺,在复合材料基体中引入SiC晶须制备出多级增强的SiCf/SiC-SiCw复合材料,并采用化学气相渗透工艺在SiC晶须表面制备BN界面层,研究了SiC晶须及其表面BN界面层对复合材料的性能影响.结果表明:在复合材料中引入SiC晶须后,由于晶须的拔出、桥连及裂纹偏转等作用增加了裂纹在基体中传递时的能量消耗,使SiCf/SiC复合材料的压缩强度有明显提高,当引入体积分数为20％的SiC晶须时,复合材料压缩强度提高了22.6％,可达673.9 MPa.通过化学气相渗透工艺在SiC晶须表面制备BN界面层后,复合材料的拉伸强度、弯曲强度和断裂韧度分别为414.0,800.3 MPa和22.2 MPa·m1/2,较SiC晶须表面无界面层时分别提高了13.9％,8.8％和19.0％.     

SiC_w/Al 复合材料轧制变形研究(英文)

研究了 SiC_w/Al 复合材料轧制变形。研究结果表明挤压后复合材料的可轧性大为改善,挤压态复合材料应垂直于晶须的取向方向进行轧制;而铸态的复合材料要获得较大的变形量必须交叉轧制。文中详细讨论了变形前后强度和塑性的变化及影响因素,分析了在两种轧制变形方式下,晶须转动和取向及轧制对晶须长径比(l/d)的影响。     

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。     

搅拌铸造SiCp/2024复合材料热挤压-轧制变形组织及性能

利用搅拌铸造-热挤压-轧制工艺制备SiCp/2024复合材料薄板。通过金相观察(OM)、扫描电镜(SEM)及力学测试等手段研究了该复合材料在铸态、热挤压态及轧制态下的显微组织及力学性能,分析了材料在塑性变形过程中显微组织及力学性能的演变。结果表明,该复合材料铸坯主要由80～100μm的等轴晶组成,粗大的晶界第二相呈非连续状分布,SiC颗粒较均匀地分布于合金基体中;热挤压变形后,晶粒沿挤压方向被拉长,SiC颗粒及破碎的第二相呈流线分布特征;轧制变形后,基体合金组织进一步细化,晶粒尺寸为30～40μm,SiC颗粒破碎明显,颗粒分布趋于均匀,轧制变形对挤压过程中形成的SiC颗粒层带状不均匀组织有显著的改善作用。数学概率统计指出,塑性变形有利于提高颗粒分布的均匀性。力学测试表明,塑性变形后,复合材料的抗拉强度、屈服强度和延伸率显著提高。SiCp/2024铝基复合材料主要的断裂方式为:合金基体的延性断裂、SiC颗粒断裂及SiC/Al界面脱粘。     

等径道角 挤压工艺对铸态 AZ91D 镁合金组织的影响

目的介绍等径道角挤压的原理及其对铸态AZ91D镁合金的组织产生的作用。方法通过确定的试验工艺参数,对AZ91D镁合金进行了等径道角挤压变形试验。使用金相显微镜和扫描电镜(SEM),对变形前后的材料进行了显微组织的观察。结果通过进行ECAE挤压后,AZ91D镁合金中的黑色共晶相(Mg17Al12)产生了回溶,在机械剪切和动态再结晶的综合作用下,晶粒得到了细化。结论通过等径道角挤压,能明显改善铸态AZ91D镁合金的组织。     

热挤压对SiCw·SiCp/2024Al组织与性能的影响

为了研究SiCw·SiCp/2024Al复合材料的热变形行为,对压铸法制备的SiCw·SiCp/2024Al复合材料进行了热挤压变形,并测定了其变形前后的室温拉伸性能.利用扫描电镜和透射电镜对复合材料热变形前后的微观组织进行观察.研究表明:增强体在基体中分布均匀,并与基体有良好的界面结合;热挤压后,纳米颗粒分布的均匀性和分散性得到改善,SiC晶须产生了沿挤压方向的定向排列,且SiC晶须与基体合金的界面结合良好;随着SiC颗粒含量的增加,混杂增强复合材料的抗拉强度随之升高,挤压后复合材料的抗拉强度进一步提高;与基体合金相比,混杂增强复合材料的延伸率下降,热挤压有利于提高混杂复合材料的延伸率.     

晶须取向对SiCw／Al复合材料力学性能的影响

研究了压铸态及挤压态20％（体积分数SiCw/6061Al复合材料中晶须取向及其拉伸力学性能,结果表明,压铸态复合材料中晶须取向趋于混乱分布状态,因而其力学性能具有较高的各向均匀性,复合材料经过挤压变形后晶须呈定向排列,沿挤压方向的各项力学性能均有所提高,尤其是伸长率得到显著改善。     

Fabrication of SiC particles-reinforced magnesium matrix composite by ultrasonic vibration

Magnesium matrix composites reinforced with two volume fractions (1 and 3%) of SiC particles (1 μm) were successfully fabricated by ultrasonic vibration. Compared with as-cast AZ91 alloy, with the addition of the SiC particles grain size of matrix decreased, while most of the phase Mg₁₇Al₁₂ varied from coarse plates to lamellar precipitates in the SiCp/AZ91 composites. With increasing volume fraction of the SiC particles, grains of matrix in the SiCp/AZ91 composites were gradually refined. The SiC particles were located mainly at grain boundaries in both 1 vol% SiCp/AZ91 composite and 3 vol% SiCp/AZ91 composite. SiC particles inside the particle clusters may be still separated by magnesium. The study of the interface between the SiC particle and the alloy matrix suggested that SiC particles bonded well with the alloy matrix without interfacial reaction. The ultimate tensile strength, yield strength, and elongation to fracture of the SiCp/AZ91 composites were simultaneously improved compared with that of the as-cast AZ91 alloy.     

Microstructure and mechanical properties of SiCp/AZ91 composite deformed through a combination of forging and extrusion process

In this paper, 10 vol.% SiCp/AZ91 magnesium matrix composites were fabricated by stir casting technology. The as-cast ingots were forged at 420 °C with 50% reduction, and then extruded at 370 °C with the ratio of 16 at a constant ram speed of 15 mm/s. The results showed that the grains were refined during forging. A much finer grain size (∼2.7 μm) of composite matrix was obtained by subjecting the as-forged composite to hot extrusion. The fine SiC particulates restricted the dynamic recrystallized grain growth during the hot extrusion processing, resulting in a remarkable grain refinement. The yield stress and ultimate tensile stress were increased in the as-extruded composite, with the reasons of eliminated casting flaws, the uniform particle distribution and grains refinement. The grain refinement and uniform particle distribution caused an obvious increase in work hardening rate in the as-extruded composite during tensile deformation at room temperature.     

Fabrication of (TiB<Subscript>2</Subscript> − TiC)<Subscript>p</Subscript>/AZ91 magnesium matrix hybrid composite

Magnesium MMCs reinforced with TiB₂−TiC particulates were fabricated successfully via a master alloy route using a low cost Al-Ti-B₄C system as starting material system. Microstructural characterization of the (TiB₂−TiC)/AZ91 composite shows relatively uniform distribution of TiB₂ and TiC particulates in the matrix material. Moreover, the results show that the hardness and wear resistance of the composites are higher than those of the unreinforced AZ91 alloy.     

石墨烯纳米片/AZ91镁基复合材料的显微组织与力学性能

采用铸造工艺制备了石墨烯纳米片(GNPs)增强的AZ91镁基复合材料,测试了复合材料的力学性能,并利用光学显微镜、X射线衍射仪、透射电子显微镜、扫描电子显微镜和能谱仪对复合材料的微观组织、界面结合和断口形貌进行了表征和分析,讨论了复合材料的强化机理。结果表明:石墨烯纳米片可有效细化镁基体的晶粒组织,在添加少量石墨烯纳米片时(0.1%),复合材料的屈服强度、延伸率和显微硬度分别为(164±5)MPa、(7.7±0.1)%和(74.2±2)HV,比基体分别提高了37.8%、13.2%和24.7%。GNPs与镁基体形成了强界面结合,这更有利于发挥应力转移强化、细晶强化等作用,提高镁合金强度、塑性等力学性能。     

Study on fracture behavior of particulate reinforced magnesium matrix composite using in situ SEM

The fracture behavior of SiCp/AZ91 magnesium matrix composite fabricated by stir casting is investigated using the in situ SEM technique. Experimental results show that (1) the dominant microcrack nucleation mode is interface decohesion in particle-dense regions because of the weak interface formed during the solidification process of the composite and large stress concentrations caused by particle segregation, (2) microcracks coalesce by the failure of matrix ligaments between microcracks while additional microcracks are initiated in the particle-dense region ahead of the coalesced microcracks, and (3) cracks propagate by coalescence of microcracks or along the particle/matrix interface. And so we come to the conclusion that the fracture mechanism of SiCp/AZ91 composite is interface-controlled. The in situ SEM observations are verified by complementary SEM studies of the fractured specimens of conventional tensile tests. And so, the in situ SEM observations can be qualitative representation on the fracture behavior of bulk SiCp/AZ91 composite.     

Influence of nano-sized carbon nanotube reinforcements on tensile deformation,cyclic fatigue,and final fracture behavior of a magnesium alloy

Magnesium alloy (AZ31) based metal matrix composite reinforced with carbon nanotubes (CNTs) was fabricated using the technique of disintegrated melt deposition followed by hot extrusion. In this research paper, the microstructure, hardness, tensile properties, tensile fracture, high cycle fatigue characteristics, and final fracture behavior of CNTs-reinforced magnesium alloy composite (denoted as AZ31/1.0 vol.% CNT or AZ31/CNT) is presented, discussed, and compared with the unreinforced counterpart (AZ31). The elastic modulus, yield strength, tensile strength of the reinforced magnesium alloy was noticeably higher compared to the unreinforced counterpart. The ductility, quantified both by elongation-to-failure and reduction in cross-section area of the composite was higher than the monolithic counterpart. A comparison of the CNT-reinforced magnesium alloy with the unreinforced counterpart revealed a noticeable improvement in cyclic fatigue life at the load ratios tested. At all values of maximum stress, both the reinforced and unreinforced magnesium alloy was found to degrade the cyclic fatigue life at a lower ratio, i.e., under conditions of fully reversed loading. The viable mechanisms responsible for the enhanced cyclic fatigue life and tensile behavior of the composite are rationalized in light of macroscopic fracture mode and intrinsic microscopic mechanisms governing fracture.     

Microstructure and strengthening mechanism of bimodal size particle reinforced magnesium matrix composite

One kind of (submicron + micron) bimodal size SiCp/AZ91 composite was fabricated by the stir casting technology. After hot deformation process, the influence of bimodal size particles on microstructures and mechanical properties of AZ91 matrix was investigated by comparing with monolithic A91 alloy, submicron SiCp/AZ91 and micron SiCp/AZ91 composites. The results show that micron particles can stimulate dynamic recrystallized nucleation, while submicron particles may pin grain boundaries during the hot deformation process, which results in a significant grain refinement of AZ91 matrix. Compared to submicron particles, micron particles are more conducive to grain refinement through stimulating the dynamic recrystallized nucleation. Besides, the yield strength of bimodal size SiCp/AZ91 composite is higher than that of single-size particle reinforced composites. Among the strengthening mechanisms of bimodal size particle reinforced composite, it is found that grain refinement and dislocation strengthening mechanism play a larger role on improving the yield strength.     

Microstructure and mechanical behavior of die casting AZ91D-Fly ash cenosphere composites

The feasibility of incorporating fly ash cenospheres in die cast magnesium alloy has been demonstrated. The effects of fly ash cenosphere additions on the microstructure and some of the salient physical and mechanical properties of magnesium alloy (AZ91D) metal matrix composites were investigated. The control AZ91D alloy and associated composites, containing 5, 10, and 15 wt.% of fly ash cenospheres (added), were synthesized using a die casting technique. A microstructural comparison showed that microstructural refinement – occurred due to the fly ash additions and became more pronounced with an increase in the percentage of the fly ash added. The metal matrix areas nearer to the fly ash particles exhibited a greater degree of refinement than was observed in the areas further away from these particles. Both filled and unfilled fly ash cenospheres, and porosity were observed in the composite microstructures. The composite specimen densities decreased and the coefficient of thermal expansion did not change significantly as the volume percent of fly ash was increased within the range investigated. The hardness values of the composite specimens exhibited an increase in proportion to the increase in percentage of added fly ash. The tensile strength of the composites also increased as the concentration of fly ash cenospheres was increased. In contrast, the Young’s modulus of these composite samples, as measured by non-destructive pulse-echo method, decreased as the percentage of fly ash in the composite was increased. SEM micrographs of the tensile fracture surfaces showed broken cenospheres on the fracture surface and evidence of ‘pull outs’, where fly ash particles were previously embedded in the matrix. Compression testing results showed that the presence of 5 wt.% cenospheres decreased the compressive strength and compressive yield strength of the composite relative to that of the AZ91D matrix alloy. Surprisingly, a significant change in compression strength was not observed for the composites with 10 and 15 wt.% cenospheres in comparison to the AZ91D matrix alloy. In contrast to the tensile tests, no cenosphere remnants were observed on the compressive test fracture surface of the composites. This observation suggests that the fracture of the composite was initiated within the AZ91D matrix by normal void nucleation and growth, followed by crack propagation through the matrix, avoiding any of the cenospheres, leading to composite fracture of the matrix.     

Fabrication of magnesium based composites reinforced with carbon nanotubes having superior mechanical properties

Magnesium (Mg) composite reinforced with carbon nanotubes (CNTs) having superior mechanical properties was fabricated using both pure Mg and AZ61 Mg alloy matrix in this study. The composites were produced via powder metallurgy route containing wet process using isopropyl alcohol (IPA) based zwitterionic surfactant solution with unbundled CNTs. The produced composites were evaluated with tensile test and Vickers hardness test and analyzed by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) equipped with energy dispersive spectroscopy (EDS) and electron back scattered diffraction (EBSD). As a result, only with AZ61 Mg alloy matrix, tensile strength of the composite was improved. In situ formed Al₂MgC₂ compounds at the interface between Mg matrix and CNTs effectively reinforced the interfacial bonding and enabled tensile loading transfer from the Mg matrix to nanotubes. Furthermore, it was clarified that the microstructures and grain orientations of the composite matrix were not significantly influenced by CNT addition.