Effect of forging temperature on the microstructures and mechanical properties of the SiC_p/AZ91 magnesium matrix composite

In this paper,10 vol.pct SiCp/AZ91 magnesium matrix composite was fabricated by stir casting technology.The ingots were forged at temperatures of 320,370 and 420℃,respectively.XRD,OM and SEM were used to characterize microstructure of the composites.It was shown that the clusters of particles in the as-cast composite were largely eliminated,and that the tensile strength was improved obviously.     

Effect of hot extrusion on microstructures and mechanical properties of SiC nanoparticles reinforced magnesium matrix composite

Particulate reinforced magnesium matrix nanocomposite prepared with semisolid stirring assisted ultrasonic vibration was subjected to extrusion at 350 °C with an extrusion ratio of 12:1. Extrusion of the SiCp/AZ91 nanocomposite induced large scale dynamic recrystallization resulting in a fine matrix microstructure. There were two kinds of zones in the extruded nanocomposite: SiC nanoparticle bands parallel to the extrusion direction and refined-grain zones between the SiC nanoparticle bands. In the SiC nanoparticle bands, there were SiC nanoparticles along the boundaries of refined grains. The distribution of SiC nanoparticles was uniform although some agglomerates of SiC nanoparticles still existed in the SiC nanoparticle bands. The ultimate tensile strength, yield strength and elongation to fracture of the SiCp/AZ91 nanocomposite were simultaneously improved by extrusion. Results from the extruded SiCp/AZ91 nanocomposite tensile testing at different temperatures (75, 125, 175 and 225 °C) revealed an increase of the tensile strength and ductility values compared with the unreinforced and extruded AZ91 alloy.     

Anti-corrosion microarc oxidation coatings on SiCP/AZ31 magnesium matrix composite

The corrosion-resistant ceramic coatings up to 80 μm thick were fabricated on SiC_P/AZ31 magnesium matrix composite by microarc oxidation (MAO) technique in Na₃PO₄ + KOH + NaF solution. The microstructure, composition and phase constituent of ceramic coatings were analyzed by SEM and XRD, and the electrochemical corrosion behaviour of coatings was evaluated by the electrochemical polarization method. The thicker coating is compact and displays a good adhesion to the composite substrate. The ceramic coatings consist of MgO, Mg₂SiO₄, MgF₂, Mg₃(PO₄)₂, furthermore, a few residual SiC phases were also found in the coatings by means of SEM observation and EDX analysis. Most of SiC reinforced particles in the oxidized composite substrate have transformed into the oxides under microarc discharge sintering, but a few residual SiC reinforcements in the MAO coatings have not disrupted the continuity of coatings. So the corrosion resistance of the SiC_P/AZ31 composite is greatly improved by MAO surface treatment, however, the corrosion resistance of coated composite also depends on the coating thickness.     

等温模锻对AZ91D镁合金组织和性能的影响

采用金相分析、拉伸试验、SEM分析等方法测试和分析了AZ91 D镁合金在铸态、锻压态及锻后+人工时效处理态下的金相显微组织和力学性能.研究表明:锻前均匀化退火能使沿晶界分布的网状βMg_(17)Al_(12)相全部溶人基体α-Mg中;等温模锻成形过程中,合金发生了明显的动态再结晶,形成细小的再结晶等轴晶粒组织,合金力学...     

真空压力浸渗制备SiCp/AZ91复合材料的显微组织、力学性能和磨损行为

采用真空压力浸透法制备SiC_p/AZ91复合材料,研究其显微组织、力学性能和耐磨性。结果表明,SiC颗粒均匀分布于金属基体中,并与基体界面结合良好。Mg₁₇Al₁₂相在SiC颗粒附近优先析出,SiC与AZ91基体的热膨胀系数失配导致高密度位错的产生,加速基体的时效析出。与AZ91合金相比,SiC颗粒的加入提高了复合材料的硬度和抗压强度,这主要是由于载荷传递强化和晶粒细化强化机制。此外,由于SiC具有优异的耐磨性,在磨损过程中形成稳定的支撑面保护基体。     

挤压铸造准晶增强AZ91D镁基复合材料组织与性能

为了改善AZ91D镁合金的性能,采用挤压铸造法制备了Mg-Zn-Y准晶中间合金增强AZ91D镁基复合材料,研究了准晶中间合金含量对复合材料组织和性能的影响。结果表明挤压铸造工艺可以有效细化晶粒,复合材料的显微组织主要由α-Mg基体、晶界上分布的β-Mg17Al12相以及Mg3Zn6Y准晶颗粒组成,准晶颗粒和α-Mg基体之间形成稳定结合。当准晶中间合金含量为5%时,抗拉强度和断后伸长率达到最大值,分别为194.3MPa和9.2%。复合材料的强化机制为细晶强化和准晶颗粒强化。     

挤压前的时效处理对AZ80镁合金组织和力学性能的影响

本文主要研究了挤压前的时效处理工艺对AZ80镁合金显微组织的力学性能的影响,同时结合扫描电子显微镜对断口进行分析。结果表明：挤压前时效处理可以明显细化晶粒;时效过程中析出的Mg₁₇Al₁₂粒子弥散分布在晶界处,在动态再结晶过程中起到阻碍晶界移动、阻止晶粒长大、细化组织的作用;随着时效时间的延长或者时效温度的提高,晶粒细化效果减弱;时效后进行挤压,材料的屈服强度、抗拉强度和延伸率均提高。通过对断口形貌的分析发现,早期裂纹产生于晶界处粗大的第二相周围,导致了拉伸过程中延伸率的下降。本文中挤压前时效处理对AZ80的强化效果为高性能镁合金的设计和开发提供了一种全新的思路。     

Effects of SiCp on microstructures of semi-solid extruded AZ91D magnesium alloys in recrystallization process

AZ91D and 8.5vol.% SiC_p/AZ91D magnesium matrix composites were fabricated by a semi-solid extruded processing method,and treated with solution and aging heat treatment.The effects of SiC_p on the microstructures of the semi-solid extruded AZ91D magnesium alloy during recrystallization were studied by observing and analyzing the microstructure evolution during extrusions and heat treatments.The results show that the addition of SiC_p inhibits the dynamic recrystallization of AZ91D during the semi-solid extrusion with only 26% of the volume fraction of recrystallization.Furthermore,the addition of SiC_p refines the sizes of grains and second phases,and upgrades the volume fraction of second phase.After solution and aging treatment,the recrystallization continues,and the addition of SiC_p promotes the recrystallization and the recrystallized microstructure is much more stable.Meanwhile,the sizes of grains and second phases continue to be refined,and the volume fraction of second phases continues to increase.     

Effect of temperature on mechanical properties of Ti-based metallic glass matrix composite

Systematic mechanical behaviors were investigated in a Ti-based metallic glass matrix (MGM) composite containing the in-situ β-dendrite phase at 100 K–298 K. We found that the yielding strength increased but the plastic strain decreased with a decrease temperature. The sharp ductile to brittle transition occurred at 100 K. The MGM composite exhibits the large work-hardening behavior at 298 K, but all sample display the work-softening behavior below 298 K. The nominal work-hardening parameter was employed to express the dependence of mechanical properties on temperatures including the brittle failure, the work-hardening and work softening behaviors. It may provide a useful way to evaluate the dependence of mechanical properties on temperatures of MGM composite.     

Transient liquid phase bonding of TiC particulate reinforced magnesium metal matrix composite （ TiCp/AZ91 D）

Microstructures and mechanical properties of transient liquid phase （TLP） bonded magnesium metal matrix composite （ MMC） joints using copper interlayer have been investigated. With an increase of bonding times from 5 min to 50 min at bonding temperature of 510 ℃ , the average concentration of copper in the bonded zone decreased, the microstructure in the zone changed from Cu, α-Mg and CuMg2 to α-Mg, CuMg2 and TiC, and mechanical properties of the joint increased. The shear strength of the joint bonded at 510 ℃ for 50 min reached 64 MPa due to the metallurgical bonding of the joint and improving its homogeneity of composition and microstructure. It is favorable to increase the bonding time for improving mechanical properties of TLP bonded magnesium MMC joint.     

AZ91筒形件旋压的组织衍化及微纳力学性能

本文采用强力正旋的方式对AZ91镁合金筒形件进行多道次旋压,通过光学显微镜(OM)和配有电子背散射衍射和能谱的扫描电子显微镜(SEM-EBSD-EDS)对不同旋压道次的微观组织衍化进行观察,结合EDS和X-Ray衍射仪（XRD）对筒形件的物相进行分析,通过纳米压痕试验仪对不同旋压道次镁合金的微区力学性能进行测试。研究结果表明：当AZ91镁合金筒形件的壁厚减薄率达到88.3%时,表面成形良好,无裂纹、褶皱产生;在旋压的初期,主要为外壁镁合金发生塑性变形,随着旋压变形量的增加,筒形件内外壁镁合金变形趋于一致,组织均匀,脆性相Mg17Al12发生破碎,呈流线形弥散地分布在镁合金内部,同时镁合金晶粒也得到细化,并发生动态再结晶;随着变形量的增加,筒形件的强度提高,硬度最高可达1.036 GPa,强化方式主要为第二相弥散强化和细晶强化。     

稀土元素Nd对AM50镁合金金相组织和力学性能的影响

以镁合金AM50为研究对象，向其中加入分别加入0．5％。1．0％和1．5％的稀土Nd。AM50合金由金属型铸造方法制备。对AM50镁合金进行了微观组织观察、力学性能测试。结果表明，合金组织随着稀土的加入得到细化。合金的各项力学性能也得到显著提高，如抗拉强度σb、硬度HB、延伸率δ等。当合金中加入1％Nd的时候，合金表现出最好的显微组织和力学性能。     

Using ARB process as a solution for dilemma of Si and SiCp distribution in cast Al-Si/SiCp composites

A major challenge in achieving the best potential of SiC_p-reinforced aluminum composites is to homogeneously disperse SiC particles within the aluminum alloys. The presence of coarse Si fibers with non-uniform distribution in cast Al-Si alloys, which may lead to poor mechanical properties, is another important problem that limits the application of these alloys. In order to eliminate these problems, accumulative roll bonding (ARB) process was used in this study as a very effective method for improving the microstructure and mechanical properties of the Al356/SiC_p composite. It was found that when the number of ARB cycles was increased, the uniformity of the Si and SiC_p in the aluminum matrix improved, the Si particles became finer and more spheroidal, the free zones of Si and SiC particles disappeared, the porosity of composite decreased, the bonding quality between SiC_p and matrix improved, and therefore mechanical properties of the composites were improved. The microstructure of the manufactured Al356/SiC_p composite after six ARB cycles indicated a completely modified structure so that its tensile strength and elongation values reached 318 MPa and 5.9%, which were 3.1 and 3.7 times greater than those of the as-cast composite, respectively.     

电磁铸造对AZ91D合金组织及力学性能的影响

研究了电磁场对AZ91D合金组织的影响 ,分析和测试了AZ91D合金挤压变形后的组织及性能。结果表明 :电磁搅拌使AZ91D合金枝晶组织发生球化和细化 ,β Mg17Al12 相数量增加 ,并使Zn元素在 β Mg17Al12 相的偏聚倾向降低 ;挤压成形后的合金极限抗拉强度高达 2 85MPa,比压铸合金提高 30 %,延伸率为 12 %,是压铸合金的 2倍多。     

挤压变形对SiCw/ZK51A镁基复合材料组织和性能的影响

利用透射电镜、扫描电镜和拉伸试验等实验方法,研究了铸态和挤压态ＳｉＣｗ／ＺＫ５１Ａ镁基复合材料的组织与力学性能。结果表明,挤压铸造ＳｉＣｗ／ＺＫ５１Ａ复合材料经等温热挤压后,其力学性能有很大提高。主要原因是：挤压变形能消除铸造缺陷,增强ＳｉＣ晶须与ＺＫ５１Ａ镁合金基体的界面结合,使复合材料中ＳｉＣ晶须发生定向分布,沿挤压方向呈准一维分布特征,晶须的增强承载能力得到充分发挥。     

Nd添加对AZ80镁合金显微组织及力学性能的影响(英文)

研究添加稀土元素Nd对AZ80镁合金显微组织及力学性能的影响。结果表明:添加1.0%Nd元素可以有效地改善AZ80合金的铸态组织,其晶粒尺寸由448μm细化至125μm,凝固组织中出现条状的Al11Nd3相和块状的Al2Nd相,且β-Mg17Al12相显著细化,由连续网状变为不连续分布。时效过程中Nd元素的添加抑制了晶界处不连续析出相的出现,并推迟合金时效峰值的出现。在AZ80合金中添加1.0%Nd时,合金的综合力学性能最佳,屈服强度、抗拉强度和伸长率分别为103.7MPa、224.0MPa和8.4%。该合金T6态的屈服强度和抗拉强度分别达到141.1和231.1MPa。     

P变质对Si合金化AZ91镁合金显微组织和力学性能的影响

采用X射线衍射、高分辨透射电镜等现代分析测试手段研究了Al-P中间合金变质处理对AZ91 0.7%Si合金的显微组织和力学性能的影响。研究结果表明:AZ91 0.7%Si合金中加入一定量的Al-P中间合金变质处理后,Mg2Si的形貌发生了显著变化,由汉字状变为细小的颗粒状,其颗粒的平均尺寸为6~10μm,且基体组织的平均晶粒尺寸由原来的100μm减小到45μm左右,β-Mg17Al12相出现不同程度的断网,从而使AZ91 0.7%Si合金的力学性能得到显著提高。说明Al-P中间合金对Si合金化的AZ91镁合金具有很好的变质强化功效,是一种Mg2Si化合物的强化粒化剂。     

Microstructural evolution and tensile mechanical properties of thixoformed AZ91D magnesium alloy with the addition of yttrium

The microstructure evolution of AZ91D magnesium alloy in the semi-solid state has been proposed or reported in previous literature. However, no detailed investigation has been conducted regarding the relationship between the microstructure and tensile mechanical properties of the thixoformed AZ91D magnesium alloy. In this paper, the microstructure of AZ91D alloy with the addition of yttrium was produced by the semi-solid thermal transformation (SSTT) route and the strain-induced melt activation (SIMA) route, respectively. Isothermal holding experiments investigated grain coarsening and the degree of spheroidization as a function of holding time in the semi-solid state. The SSTT route and the SIMA route were used to obtain the semi-solid feedstock for thixoforming. The results show that solid particles of the SSTT alloy are spheroidized to some extent but the previous irregular shape is still obvious in some of them. While the SIMA alloy exhibits ideal, fine microstructure, in which completely spheroidized solid particles contain little entrapped liquid. The microstructure of the SSTT alloy is less spheroidized compared with the SIMA alloy under the similar isothermal holding condition. As the holding time increases, the mean solid particle size of the SSTT alloy decreases initially, then increases, while the mean solid particle size of the SIMA alloy increases monotonously at 560 °C. Compared with the SSTT alloy, the SIMA alloy obtains finer grains under the similar isothermal holding condition. The mechanical properties of the thixoformed AZ91D alloy with the addition of yttrium produced by the SIMA route are better than those of the thixoformed alloy produced by the SSTT route. The ultimate tensile strength, yield strength and elongation for the thixoformed alloy produced by the SIMA route are 303.1 MPa, 147.6 MPa and 13.27%, respectively. The tensile properties for the AZ91D alloy with the addition of yttrium thixoformed from starting material produced by the SIMA route are better than those of the AZ91D alloy with the addition of yttrium thixoformed from starting material produced by the SSTT route.