时效温度对SCFs/AZ31B复合材料组织和性能的影响

目的 探究提高固相合成SCFs/AZ31B镁基复合材料力学性能的最佳时效温度.方法 采用固相合成工艺制备SCFs/AZ31B镁基复合材料并在415℃固溶处理20 h,然后分别在155,175,195,215℃下进行20 h时效处理.采用金相显微镜(OM)与扫描电镜(SEM)观察微观组织,并测试拉伸性能、硬度等力学性能,研究时效温度对显微组织及力学性能的影响.结果 时效过程中,碳纤维稳定存在于基体中.随着时效温度的升高,晶粒尺寸先增加后减小,175℃时效晶粒尺寸最小为14.84μm,时效析出的第二相为Al2Mg.当时效时间为20 h、时效温度为175℃时,材料的屈服强度、抗拉强度、伸长率和维氏硬度最高,分别为188 MPa,259 MPa,6.9％,70.2HV.在该实验条件下,最佳时效温度为175℃.结论 随着时效温度的升高,第二相从非连续析出转为连续析出.时效处理可以改善材料的力学性能.     

AZ91D镁合金凝固过程分析

采用差热法以及冷却曲线测定AZ91D镁合金的相变温度,通过金相试验,研究了AZ91D镁合金凝固过程中显微组织的变化,为制定合理的AZ91D镁合金热处理工艺,提高合金力学性能提供了依据.     

AZ10镁合金均匀化退火工艺研究

通过金相组织分析、显微硬度测试和热压缩实验,研究了不同退火温度和时间条件下AZ10镁合金铸坯的显微组织、显微硬度、热压缩变形抗力以及变形能,分析了退火温度和时间对铸坯组织转变、成分均匀化、变形抗力和变形能的影响.结果表明,退火温度对均匀化起主要作用,AZ10镁合金铸锭的均匀化退火的优化工艺为400 ℃×18 h.     

热处理对AZ91D及AZ71镁合金组织及力学性能的影响

研究了热处理工艺对AZ91D及AZ71镁合金显微组织及力学性能的影响。结果表明,在AZ91D和AZ71镁合金中,温度升高,β相含量都是先增加后减小,400℃时合金中的β相几乎消失,完全由α基体相组成;硬度都是先减小后增加,235℃时硬度最大;耐冲击性都是先减小后增加,235℃时耐冲击性最低。     

Cu-Ni-Si合金的时效析出与再结晶

通过分析时效期间Cu-Ni-Si合金显微硬度、导电率及微观组织的变化,研究了析出相和再结晶行为的相互作用,以期为该合金多级复合工艺的制定提供参考.研究发现,时效初期析出相对随后的再结晶过程具有强烈阻碍作用.在450、550℃较低温度时效时,合金发生原位再结晶,析出相在其体积分数略微升高或不变的情况下发生粗化;导电率上升趋势为先快后慢并趋于稳定,因而其变化曲线上无峰值出现;显微硬度则由于时效后期析出颗粒粗化,析出强化效果降低而出现峰值.在750℃高温时效时,合金发生不连续再结晶,析出相在体积分数略有降低的情况下发生粗化;导电率先快速上升后缓慢下降,因而出现峰值,而显微硬度由于析出物迅速粗化,一开始就表现为持续下降.     

AZ61镁合金的均匀化处理

研究了不同退火温度和时间条件下AZ61铸态镁合金的显微组织以及硬度值,分析了温度和保温时间对组织转变和成分均匀性的影响.得出温度是影响均匀化进程的主要因素,并推荐AZ61铸态镁合金的退火工艺为400 ℃×12 h.     

热处理对AZ91D及AZ71镁合金组织及力学性能的影响

研究了热处理工艺对AZ91D及AZ71镁合金显微组织及力学性能的影响。结果表明，在AZ91D和AZ71镁合金中，温度升高，β相含量都是先增加后减小，400℃时合金中的口相几乎消失，完全由α基体相组成；硬度都是先减小后增加，235℃时硬度最大；耐冲击性都是先减小后增加，235℃时耐冲击性最低。     

退火工艺对 AZ61镁合金铸坯组织及加工性能的影响

研究了均匀化退火对AZ61半连续铸锭的组织及变形性能的影响.通过组织观察、显微硬度测量以及在1500D Gleeble实验机上进行热压缩并计算变形能,分析比较了均匀化温度和时间对坯料组织和变形性能的影响.结果表明:均匀化退火有利于消除铸态组织中的枝晶偏析,不同均匀化退火工艺对第二相化合物的存在方式存在影响;AZ61镁合金硬度值随着退火温度的升高呈降低趋势;退火温度越高,AZ61镁合金热变形峰值应力大小随保温时间的波动逐渐变大;AZ61镁合金优化的退火工艺参数为400 ℃×12 h.     

漂珠/AZ91D镁合金复合材料的高温压缩变形行为

采用搅拌铸造法制备了漂珠(FAC)/AZ91D镁合金复合材料。研究了该复合材料的高温压缩变形行为,分析了压缩变形温度和应变率对FAC/AZ91D镁合金复合材料压缩变形行为的影响规律,并计算了其热变形激活能。结果表明:FAC/AZ91D镁合金复合材料的高温压缩真应力-真应变曲线分为4个阶段:弹性变形、加工硬化、峰值应力和稳态流变阶段。相同应变率下,FAC/AZ91D镁合金复合材料的峰值应力和稳态流变应力随压缩变形温度的升高而降低;相同压缩变形温度下,流变应力随应变率增大而升高。在相同应变率或相同压缩变形温度下,FAC/AZ91D镁合金复合材料的热变形激活能随压缩应变率或压缩变形温度的升高而增大,其热压缩行为可以用双曲正弦函数形式的Arrhenius关系来描述。压缩变形温度与应变率对FAC/AZ91D镁合金复合材料的高温压缩组织均有重要影响。提高压缩变形温度或增大应变率,均可加速动态再结晶的进程。     

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。     

Relationship between age-hardening by continuous precipitation and damping capacity in AZ91 alloy

The strain-amplitude-dependent and strain-amplitude-independent damping capacities of a cast AZ91 magnesium alloy as functions of its age-hardening response induced by continuous precipitation have been investigated. The damping capacities of the AZ91 alloy exhibited a decreasing tendency in the order of solutionised, underaged, overaged, and peak aged states in the strain-amplitude-dependent region, whereas they increased continuously with aging time in the strain-amplitude-independent region. In view of the microstructural evolution during aging, the lower Al concentration in the α-(Mg) matrix and the lower number density of continuous precipitates are thought to be responsible for the better damping capacities of the AZ91 alloy in the strain-amplitude-independent and strain-amplitude-dependent regions, respectively.     

Microstructure evolution of thixomolding AZ91D magnesium alloy during heat treatment

The microstructure evolution of thixomolding AZ91D magnesium alloy during heat treatment was investigated by means of SEM, XRD, and Vickers hardness measurement. The thixomolding AZ91D alloy has faster β phase dissolution kinetics in comparison with the HPDC alloy at 415 °C solution treatment. Both the discontinuous precipitation and the continuous precipitation were observed during aging treatment. The thixomolding specimen exhibited an accelerated age-hardening kinetics in comparison with the HPDC specimen.     

Microstructure and Mechanical Behavior of Squeeze Cast SiCw/AZ91 Magnesium Matrix Composites

［1］S.Ryu, J.Kaneko and M.Suganuma: J. Japan Inst. Metals, 1997, 61, 1160. ［2］H.Hu: J. Mater. Sci., 1998, 33, 1579. ［3］B.L.Mordike, K.U.Kainer and B.Sommer: in Proc.3rd Inter. Magnesium Conf., Manchester, UK, 1996, 637. ［4］S.Kamado, T.Shikawa, T.Wada and Y.Kojima: J. Japan. Inst. Light Metal, 1996, 46, 71. ［5］M.Vedani, E.Gariboldi, G.Silva and C.Di. Gregorio: Mater. Sci. Tech., 1994, 10, 132. ［6］B.R.Henriksen and T.E.Johnsen: Mater. Sci. Tech.,1990, 6, 857. ［7］Mingyi ZHENG: Ph.D. Thesis, Harbin Institute of Technology, 1999. (in Chinese)     

Microarc oxidation coating formed on SiCw/AZ91 magnesium matrix composite and its corrosion resistance

A ceramic coating was synthesized on the surface of SiCw/AZ91 magnesium matrix composite by means of microarc oxidation (MAO) technique. Scanning electron microscope (SEM) was employed to characterize the surface morphology and cross-section microstructure of the coating. The phase structure and the chemical composition of the ceramic coating were analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The corrosion resistance of the coating was evaluated by immersion test and electrochemical method. The results showed that the corrosion rate of the coated SiCw/AZ91 composite was decreased greatly compared with that of the bare composite because of the protective microarc oxidation coating.     

T4 热处理对石膏型 AZ91 铸造镁合金组织和性能的影响

用石膏型熔模铸造技术,成功制备了AZ91镁合金铸件.用金相显微镜(OM)、扫描电镜(SEM)、能谱(EDS)以及电子万能实验机等,研究了AZ91镁合金铸态及T4热处理态的显微组织演变和力学性能.结果表明,分布在铸态AZ91镁合金晶界的网状β-Mg17Al12相在T4热处理过程中逐渐溶解,铸态和T4热处理态中均存在大量的A18Mn5化合物,T4处理后,其力学性能显著提高.     

AZ91 Magnesium Alloy/Porous Hydroxyapatite Composite for Potential Application in Bone Repair

AZ91/HA composite was prepared by AZ91 magnesium alloy and porous HA using squeeze casting method.The microstructure and mechanical property of the AZ91/HA composite were studied. The results show that the molten AZ91 alloy completely infiltrated the preform without destroying the porous structure of the HA preform. The compressive strength of AZ91/HA composite increased significantly compared with that of the porous HA. The immersion test indicated that AZ91 alloy shows a lower corrosion resistance and is easier to be corroded in comparison with HA.     

Microstructures and wear property of friction stir welded AZ91 Mg/SiC particle reinforced composite

The microstructures and wear property of friction stir welded AZ91 Mg alloy/SiC particle reinforced composite (AZ91/SiC/10p) were investigated. The initial microstructures of the AZ91/SiC/10p were composed of irregularly distributed β-phases (Al₁₂Mg₁₇) and agglomerated SiC particles, while the friction stir weld zone was characterized by the homogeneous distribution of SiC particles, the recrystallized grain structure and the dissolution of β-phase. Thank to the microstructural modification, an improvement in the hardness and wear property of the weld zone were observed as compared to those of the base metal. The hardness near the weld zone was a higher and more homogeneously distributed and the wear resistance within the weld zone, as evaluated by the specific wear loss, was superior, as compared with the base metal.     

Effects of Ca combined with Sr additions on microstructure and mechanical properties of AZ91D magnesium alloy

Abstract

Weight reduction to improve automobile fuel economy has triggered renewed interest in magnesium. The effects of Ca/Sr separate and composite additions to AZ91D magnesium alloy on its microstructure and mechanical properties have been investigated. The results indicate Ca can refine both the grain and eutectic phase of AZ91D magnesium alloy. Sr hampers microstructure refinement when composite Ca/Sr additions are made. In addition, separate Ca additions to AZ91D magnesium alloy increase yield strength but decrease elongation of this alloy. By adjusting the Ca/Sr composite proportions, additions to AZ91D magnesium alloy are able to improve both microstructure and mechanical properties of the alloy.