Creep mechanism of as-cast Mg-6Al-6Nd alloy

The creep mechanism of as-cast Mg-6Al-6Nd alloy was studied. The stress exponent for creep is 5.8 under the applied stresses of 50–70 MPa at 175°C. The activation energy for creep is 189 kJ·mol⁻¹ under the applied stress of 70 MPa in the range of 150–200°C. The true stress exponent and threshold stress for creep are calculated as 4.96 and 10.2 MPa, respectively. The true stress exponent indicates that its creep mechanism belongs to the dislocation climb-controlled creep, which is in agreement with the microstructure changes before and after creep. The high value for stress exponent is attributed to the interaction of Al₁₁Nd₃ phase with dislocations. The activation energy is more than the self-diffusion activation energy of Mg, which is attributed to the load transfer taking place from the matrix to Al₁₁Nd₃ phase during creep.     

Effect of rare-earth element Sm on the corrosion behavior of Mg-6Al-1.2Y-0.9Nd alloy

The effect of Sm (0 wt.%-2 wt.%) addition on the corrosion behavior of Mg-6Al-1.2Y-0.9Nd alloy in 3.5 wt.% NaCl solution has been studied by static corrosion tests, corrosion morphology observation, corrosion scale and microstructure analysis. The results show that, with the increasing of Sm content, the corrosion rate of the alloy decreases at first, then increases and reaches the valley at 0.5 wt.% Sm. The reason is that the proper content of Sm addition can refine the precipitates and make the component and microstructure uniform, and therefore, it remarkably improves the corrosion resistance of the alloy.     

Effect of Ti-6Al-4V particle reinforcements on mechanical properties of Mg-9Al-1Zn alloy

Mg-9Al-1Zn (AZ91) magnesium matrix composites reinforced by Ti-6Al-4V (TC4) particles were successfully prepared via powder metallurgical method. The yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) showed a mountain-like tendency with the increase of the TC4 content. The mechanical properties of AZ91 magnesium matrix composites reached the optimal point with TC4 content of 10 wt.%, realizing YS, UTS, and EL of 335 MPa, 370 MPa, and 6.4%, respectively. The improvement of mechanical properties can be attributed to the effective load transfer from the magnesium matrix to the TC4 particles, dislocations associated with the difference in the coefficient of thermal expansion, good interfacial bonding between the Mg matrix and TC4 particles, and grain refinement strengthening.     

Effects of Sb,Sm, and Sn additions on the microstructure and mechanical properties of Mg-6Al-1.2Y-0.9Nd alloy

The microstructure and mechanical properties of Mg-6Al-1.2Y-0.9Nd magnesium alloy with Sb, Sm, or Sn addition were investigated through X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The results show that small amounts of Sb, Sm, and especially Sn can refine the grains of the alloy. High melting point Sb₃Y₅, Al₂Sm, and Nd₅Sn₃ intermetallic compounds can be formed respectively when Sb, Sm, and Sn are added to the alloy. Sb and Sm can improve the tensile strength of the alloy at ambient and elevated temperatures. The tensile strength of the alloy with Sm addition is the highest at 293 and 423 K. However, the tensile strength of the alloy with Sn addition is the highest at 448 K.     

Mg-5.5Al-0.5Y-xSm合金的显微组织和力学性能

采用XRD、OM、SEM和EDS等手段研究了Mg-5.5Al-0.5Y-xSm(x=0~2.0%)合金的显微组织和力学性能。实验结果表明,加入适量的Sm后,合金晶粒和Al2Y相得到细化,Mg17Al12相数量减少,同时基体中出现高熔点相Al2Sm相。随着Sm含量的增加,合金的室温(25℃)和高温(150℃和175℃)力学性能先升高后降低,且在Sm含量为1%时达到最佳。     

Microstructure and creep properties of Mg-4Al-2Sn-1 （Ca,Sr） alloys

The effects of Ca and Sr addition on the microstructure and creep properties of Mg-4Al-2Sn alloys were examined.Tensile tests at 25℃ and 200℃ and creep tests at 150℃ and 200℃ were carried out to estimate the room temperature and high temperature mechanical properties of these alloys.The microstructure of the Mg-4Al-2Sn alloy showed dendriticα-Mg,Mg17Al12 and Mg2Sn phases.The latter two phases precipitated along the grain boundaries.The addition of Ca and Sr resulted in the formation of ternary CaMgSn and SrMgSn phases within the grain.The grain size was reduced slightly with the addition of Sr and Ca.The tensile strength was decreased by the addition of Ca and Sr at room temperature.However,the high temperature tensile strength was increased.The creep strength was improved by the addition of Ca and Sr.     

ZK60镁合金ACPP挤压棒材组织演变及其时效析出强化

利用630T挤压机对ZK60镁合金棒材挤压工艺进行试验研究。设计了分流环形通道焊合挤压(ACPP)模具。通过对坯料、ACPP挤压态和ACPP挤压态+人工时效热处理三种状态下的性能进行了测试和分析。通过在420 ℃下的ACPP,成功地挤出了超级细晶ZK60镁合金棒材。试验结果表明,在前期的分流和等通道挤压过程中晶粒已经有一定程度的细化,在进行了焊合完成整个ACPP挤压之后,晶粒细化更为明显。最终晶粒尺寸大多在20～30 μm之间。室温下的挤压态抗拉强度为312 MPa,通过人工时效热处理后的抗拉强度为331MPa,析出强化是抗拉强度高的主要原因;这两个状态对应的硬度分别是59 HV和57 HV。     

Coherent strengthening of aging precipitation in rapidly solidified Cu-Cr alloy

1INTR0DUCTIONHavinghighstrengthandgoodelectricalandthermalconductivities,Cu-Cralloysareusedinanumberofengineeringapplications,suchaselectricresistanceweldingelectrode,thelinertubeofcontinuouscastingcrystallizer,integrat-edcircuitleadframe,stiltwire0felectricloco-motive.However,higherstrengthismoreandmorerequiredforc0pperalloyswiththerapiddevelopmentofelectronicindustry.Forexam-ple,tensilestrengthdb>600MPa,hardnessHV>180andconductivity>80%(IACS)arede-mandedforleadframematerialsinverylar…     

Mg-9AI-6Si镁合金组织及性能研究

利用普通重力铸造方法,制备了Mg-9Al-6Si镁合金.用光镜(OM),扫描电镜和能谱仪(SEM/EDS)研究了铸态Mg-9Al-6Si镁合金的显微组织,用XRD分析了合金的相组成,测试了合金室温拉伸力学性能和硬度,用SEM观察了合金拉伸断口形貌.结果表明:Mg-9Al-6Si镁合金铸态组织主要由α-Mg基体和分布在其上的粗大棱状枝晶或多边形块状初晶Mg2Si相及连成网状的β-Mg17Al12相组成,无汉字状Mg2Si相.该合金室温拉伸断口是以准解理断裂为主的脆性断裂,断裂沿α-Mg基体和Mg2Si相的界面处产生并扩展,抗拉强度为137.45 MPa,硬度为123 Hv1.     

挤压Mg-(8,11)Al-Mn-Y-Gd-La合金的显微组织和力学性能

研究了添加稀土元素的不同高铝含量的变形挤压态镁合金的微观组织和力学性能。结果表明,铝含量的增加,挤压合金晶粒的得到了明显的细化,平均晶粒尺寸为(12±4)μm。挤压态合金的显微硬度高于固溶态合金的显微硬度;随着铝含量的增加,合金的时效硬化行为得到明显的改善。这些主要是由于在挤压过程中晶粒的细化和沿着挤压方向第二相的析出。另外,随着铝含量的增加,合金的屈服强度和抗拉强度也有所提高,分别达到了306和348 MPa。这主要取决于晶粒的进一步细化和析出相体积分数的增加。因镁稀土相和β-Mg17Al12相都为脆性相,铝含量的增加引起析出相体积分数的增加,也同时导致合金的伸长率有所下降。     

Experiments and modeling of double-peak precipitation hardening and strengthening mechanisms in Al-Zn-Mg alloy

The aim of the present work is to develop a model for simulating double-peak precipitation hardening kinetics in Al-Zn-Mg alloy with the simultaneous formation of different types of precipitates at elevated temperatures based on the modified Langer-Schwartz approach. The double aging peaks are present in the long time age-hardening curves of Al-Zn-Mg alloys. The physically-based model, while taking explicitly into account nucleation, growth, coarsening of the new phase precipitations and two strengthening mechanisms associated with particle-dislocation interaction (shearing and bypassing), was used for the analysis of precipitates evolution and precipitation hardening during aging of Al-Zn-Mg alloy. Model predictions were compared with the measurements of Al-Zn-Mg alloy. The systematic and quantitative results show that the predicted hardness profiles of double peaks via adding a shape dependent parameter in the growth equation for growth and coarsening generally agree well with the measured ones. Two strengthening mechanisms associated with particle-dislocation interaction (shearing and bypassing) were considered operating simultaneously in view of the particle size-distribution. The transition from shearing to bypassing strengthening mechanism was found to occur at rather early stage of the particle growth. The bypassing was found to be the prevailing strengthening mechanism in the investigated alloys.     

Enhancement of mechanical properties of duplex Mg-9Li-3Al alloy by Sn and Y addition

For enhancement of mechanical properties in Mg-9Li-3Al alloys, Mg-9Li-3Al duplex alloys were alloyed by addition of Sn and Y. Microstructure evolution and mechanical property response of as-cast Mg-9Li-3Al alloys by alloying with Sn and Y were investigated by optical microscopy, scanning electron microscopy, X-ray diffractometry and tensile tests. The results indicate that considerable blocky dendrites of primary α phase in Mg-9Li-3Al alloys become lath-like due to the addition of Sn. With addition of Y, Mg-9Li-3Al alloy consists of both block-like and lath-like α-Mg dendrites. The as-cast Mg-9Li-3Al-1Sn-1Y alloy shows a yield strength of 118 MPa, ultimate tensile strength of 148 MPa and the elongation to failure of 21%. Improvement in both strength and elongation of Mg-9Li-3Al alloys with Sn and Y addition is attributed to the combined action of MgLi₂Sn and Al₂Y intermetallic compounds.     

复合挤压对Mg-4Sn-2Al-1Zn合金组织及力学性能的影响

针对镁合金室温强度低、塑性差的问题,采用复合挤压工艺在250℃对Mg-4Sn-2Al-1Zn合金进行了挤压,研究了复合挤压对合金的组织演变、织构及力学性能的影响。结果表明,复合挤压能将Mg-4Sn-2Al-1Zn合金的晶粒尺寸由45.2μm细化至3.1μm,组织均匀。挤压后的合金硬度提升,均匀性改善,屈服强度、抗拉强度和断后伸长率分别为204 MPa、287 MPa和21.0%,较匀质态分别提高了140.0%、91.3%和156.1%。动态再结晶是晶粒细化的主要机制,晶粒细化以及挤压后基面织构增强、织构向挤压方向均匀扩展使合金强度、塑性提高,挤压过程中Mg2Sn相破碎进一步提高了合金的力学性能。上述研究表明复合挤压是一种能有效提高镁合金综合性能的工艺。     

Si含量对Mg-8Zn-4Al-0.3Mn镁合金时效过程的影响

采用光学显微镜、扫描电镜(附EDAX能量分散光谱系统)和差示扫描量热仪(DSC)等分析手段研究了不同Si含量(0～1.61wt%)对Mg-8Zn-4Al-0.3Mn(ZA84)合金时效过程的影响。结果表明,合金经固溶处理后显微硬度较铸态下提高了8%左右,其Mg2Si、τ(Mg32(Al,Zn)49)等相基本未溶入基体中。随着ZA84合金中加入Si量的增加,合金的析出相形成激活能呈增加趋势,峰值时效时间由ZA84合金的2h左右推迟至8h左右,析出相粗化时间较ZA84合金推迟4h以上。合金中加入不同含量Si后其峰值时效显微硬度提高幅度为4%～12%。     

Zn添加对Mg-8Al-2Sn镁合金组织和性能的影响

本文以Mg-8Al-2Sn变形镁合金为研究背景,通过在Mg-8Al-2Sn合金中添加0-2 wt.%含量的Zn元素,研究了Zn添加对Mg-8Al-2Sn挤压镁合金显微组织和性能的影响。研究结果表明,铸态Mg-8Al-2Sn-xZn合金的相组成主要是α-Mg相、Mg₁₇Al₁₂相和Mg₂Sn相。在添加Zn元素以后,合金中的共晶化合物的形态发生变化,由共晶组织变为离异共晶组织。挤压过后,晶粒组织尺寸更均匀。Zn元素的加入,会促进合金中第二相在挤压过程中的动态析出以及第二相尺寸的粗化。合金在时效中产生的析出相的数量也随着Zn含量的增多而增加。随着Zn含量的增加,挤压态和时效态合金的屈服强度和抗拉强度都随之增加。当Zn含量达到2 wt.%时,合金力学性能最好,其时效态的抗拉强度,屈服强度和延伸率分别是385 MPa, 291 MPa和6.44%。     

Si对铸态Al-5.3Cu-0.8Mg-0.6Ag合金显微组织与时效析出的影响

通过熔炼铸造法制备了一系列含Si的Al-Cu-Mg-Ag合金,采用金相观察、扫描电镜(SEM)、透射电镜(TEM)及硬度测试,研究了Si的添加对铸态合金的显微组织与时效过程影响。结果表明,高含量Si的添加降低了铸态合金的时效硬度与高温耐热性能,延长了铸态合金在185℃时的峰时效时间,完全抑制了基体合金中强化相-Ω相的析出。含6.0%Si的Al-5.3Cu-0.8Mg-0.6Ag合金的强化相主要由θ′相及少量σ相(Al5Cu6Mg2)组成。     

Mg-12Zn-xCa合金T6处理后的组织与硬度

研究了铸态Mg-12Zn-xCa(x=0、1、2、3)合金T6处理后的组织与硬度。结果表明,铸态Mg-12Zn-xCa合金经T6处理后,组织中α-Mg相由枝晶变为等轴晶且细化,硬度提高。随着Ca含量增加,T6处理Mg-12Zn-xCa合金组织细化,硬度提高,但Ca含量超2%时,组织出现枝晶化,硬度降低。     

Nd变质过共晶Al-17.5%Si合金的微观组织和断口形貌

采用单一稀土元素Nd对过共晶Al-17.5%Si合金进行变质;采用扫描电镜、金相显微镜、电子探针、透射电镜及X射线衍射等方法对变质前后合金的微观组织、成分和相组成进行分析;并对变质前后合金的断口形貌进行分析.结果表明:加入0.3%Nd(质量分数)到过共晶Al-17.5%Si合金中可同时变质初生硅和共晶硅,经过变质处理后,初生硅的形状由星形和不规则形状变为块状,尺寸由40～60 μm减小到10～30 μm,共晶硅由长针状变成球状或短棒状;初生硅区域的主要成分是硅,中心边缘几乎检测不到Nd元素,Nd沿晶界分布;与未变质合金相比,经0.3%Nd变质后的Al-17.5%Si合金硅相上孪晶密度增大,变质后的合金中没有生成新相,a(Al)相和硅相的晶格常数变大;经0.3%Nd变质后,合金的整体性能大幅度提高,抗拉强度提高了35.8%,从120 MPa提高到163 MPa,伸长率从0.8%提高到2.2%,提高了175%.