Nd对AM50力学性能及高温性能的影响

对加Nd的AM50镁合金铸态试样进行固溶处理(420℃/12 h),研究了Nd对其显微组织、力学性能和抗高温蠕变性能的影响.结果表明:Nd的加入细化了晶粒,导致AM50合金室温力学性能的提高.Nd在AM50合金中形成了Al11Nd3高温稳定相,Al11Nd3的存在使加Nd的AM50合金在200℃的稳态蠕变率及高温(150℃)力学性能大幅度提高.     

片层宽度对全片层TiAl合金蠕变性能的影响

通过不同的热处理工艺。得到了具有相近晶粒度不同片层宽度的全片层TiAl合金组织，并在T=800℃，σ=205MPa条件下，测试了其蠕变性能，研究了片层宽度对蠕变性能的影响规律及其机理。研究结果表明，全片层TiAl合金的初始蠕变量和最小蠕变速率随片层宽度的增加而提高。片层界面在蠕变过程中能向基体中发射位错。同时又能阻碍位错的发射和位错的运动。     

Si对AM30变形镁合金组织和力学性能的影响

为了提高Mg-3Al-0.4Mn合金的常温力学性能,研究了铸态和挤压态下Si含量对AM30合金的组织和力学性能的影响.结果表明,增加Si的添加量会生成粗大的汉字状的Mg2Si相,不利于提高合金的力学性能;但经过挤压后,呈汉字状Mg2Si相破碎,变成颗粒细小的Mg2Si相,晶粒细化,有利于提高合金的性能.     

挤压AM50(-Ca)镁合金的显微组织与力学性能研究

研究了挤压AM50(-Ca)镁合金的微观组织和力学性能.研究发现添加钙在AM50合金中生成新的Al2Ca相,并细化合金的晶粒尺寸.大于2wt.%的钙使铸态AMS0的晶粒尺寸从200 μm减小到40 μm,使挤压态AM50的晶粒尺寸从15 μm减小到7.5 μm.含钙量较少时,晶粒内仍含有少量的Mg17Al12相,Al2Ca相主要分布在晶界;含钙量多于2wt.%时,合金中的Mg17Al12完全消失,除晶界处的Al2Ca相外,在晶粒内部出现大量的针状Al2Ca相.加钙提高了AM50合金的低温抗拉强度,同时在所有试验温度下合金的屈服强度得到提升.     

稀土镁合金抗高温蠕变性能的研究进展

稀土元素在镁合金中能够细化晶粒尺寸,可以利用其固溶强化和第二相强化机制提高合金力学性能,改善镁合金的抗高温蠕变能力。介绍了镁合金的蠕变机理,以及稀土Y元素、Gd元素、Sc元素和Ce元素对镁合金组织和蠕变性能的影响,综述了目前国内外开发的Mg-Y、Mg-Gd、Mg-Sc、Mg-Ce等一系列稀土镁合金的研发现状,对稀土镁合金的发展现状给予意见,并对稀土镁合金的发展前景进行展望。     

Fe3Al基合金力学性能和显微组织的关系研究

显微组织对Ｆｅ３Ａｌ基合金的室温和高温力学性能以及抗蠕变性能有较大影响。研究表明，减少横向晶界并不是提高Ｆｅ３Ａｌ合金室温塑性的最途径。     

低铌新锆合金的抗蠕变性能

通过对低铌新锆合金板材的蠕变性能数据和变形亚结构的分析,探讨了低铌新锆合金的蠕变过程及其抗蠕变性能.结果表明,①工业规模生产的1.4 mm厚的Zr-1Sn-0.3Nb-0.3Fe-0.1Cr合金板,在400℃,3种应力(117 MPa,137 MPa,157 MPa)条件下,200 h的蠕变,第2阶段的时间-应变关系分别为:117 MPa时,ε=0.24676+0.0189t(R=99.9%);137 MPa时,ε=1.95822+0.03417t(R=99.8%);157 MPa时,ε=6.17578+0.15793t(R=98.0%).②低铌新锆合金的蠕变速率远低于Zr-4合金.     

ECAP变形对Mg2Si增强耐热镁合金组织及性能的影响

为了提高镁合金的耐热性能,在Mg-Zn合金中加入Si,形成Mg-Zn-Si镁合金.采用ECAP工艺在变形温度为573 K和挤压路径为Bc条件下对Mg-Zn-Si镁合金进行不同道次的变形.运用金相显微镜(OM)、X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等手段对变形后的Mg-Zn-Si镁合金进行了组织表征,对变形后的合金进行了室温拉伸和高温蠕变等力学性能测试.结果表明:随着挤压道次增加,α-Mg基体、Mg Zn相及Mg2Si相均得到细化且分布趋于均匀.1道次挤压后部分基体α-Mg细化,4道次挤压后α-Mg的尺寸减小为5~10μm,且晶粒大小趋于均匀;2道次挤压后Mg2Si相枝晶在原位置破碎为颗粒状,6、8道次挤压后Mg_2Si相呈弥散分布.4道次挤压后合金的屈服强度和抗拉强度均提高120%,伸长率提高353%;8道次挤压后合金的抗拉强度和伸长率与4道次相比变化不大,但屈服强度进一步提高了19%.随着挤压道次增加,高温抗蠕变性能提高,8道次后高温稳态蠕变速率降低5倍.Mg2Si相细化机理为受剪切而机械碎断.     

锰对Al—Cu合金固液态区间蠕变及应力松弛的影响

在自行研制的流变性能测试装置上研究了锰对Ａｌ－５％Ｃｕ合金固液态区间蠕变和应力松弛的影响，考察了锰加入量对合金蠕变，蠕变速率及残余应力的影响程度。研究结果表明，锰能不同程度地减少合金的蠕变量，降低蠕变速率。此外，锰还能使残余应力提高。锰加入量增加，效果显著。     

Ca对Mg-8Zn-3.2Al-0.9Si-0.3Mn合金显微组织及性能的影响

采用光学显微镜(OM)、X射线衍射仪(XRD)、带能谱分析(EDS)的扫描电子显微镜(SEM)等分析手段研究了元素Ca对Mg-8Zn-3.2Al-0.9Si-0.3Mn合金基体及Mg2Si相的细化效果及其细化机制。结果表明:Ca的加入能够使Mg2Si初生相由粗大的汉字状变为细小、弥散分布的颗粒状,并使合金基体组织显著细化。Ca对Mg2Si相的变质是以CaSi2作为Mg2Si相的异质形核核心和Ca作为表面活性元素影响其生长两种机制共同作用的结果。由于显微组织的改善,使得合金的室温和高温力学性能均得到提高。     

Effect of Sn on the Microstructure and Mechanical Properties of Mg-5Al-2Si Alloys

The effect of Sn addition on the microstructures and mechanical properties of Mg-5Al-2Si alloys was investigated with variations of Sn contents （3 and 6 wt pct）. The microstructure of the alloy was characterized by the presence of Mg2Sn particles within matrix and at grain boundaries. As the Sn contents increased, yield and ultimate tensile strength were increased at room temperatures and 150℃. Creep properties were improved with the increasing amount of Sn due to the fine precipitation of Mg2Sn phases within grain during creep.     

Microstructures and mechanical properties of AZ91 alloy with combined additions of Ca and Si

Ca and Si additions to AZ91 alloy have been investigated and the results show that addition of Ca or Ca combined with Si resulted in the refinement of the as-cast microstructure, increase the thermal stability of β phase and the inhibition of discontinuous precipitations. Small amounts of Ca added to the AZ91 alloy mainly dissolved into β phase and raised the thermal stability of the phase, thus strengthening the alloy at elevated temperatures. Combined additions of Si with Ca to the AZ91 alloy were more effective on increasing the tensile strength at both ambient and elevated temperatures. The creep resistance of the alloy was also improved significantly in the alloy with Ca and Si additions. The creep rate of the alloy containing 0.3% Ca and 0.6% Si, tested at 473 °K and 50 MPa, was one order of magnitude lower than that of the base alloy (without Ca and Si addition). The mechanism of mechanical properties improvement caused by Ca and Si was also discussed.     

Effect of Sr on microstructure,tensile properties and wear behavior of as-cast Mg–6Zn–4Si alloy

The microstructure, tensile properties and wear behavior of as-cast Mg–6Zn–4Si alloy with strontium additions at ambient and elevated temperature were investigated by means of X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), standard high temperature tensile testing and a pin-on-disc type apparatus. The results indicated that the grain size of the primary Mg₂Si decreased initially and then gradually increased with increasing Sr amount. Meanwhile, the morphology of the primary Mg₂Si in the alloys changed from large dendritic to polygonal or fine block, and that of the eutectic Mg₂Si phase turned to fine fibre with increasing Sr content. Tensile testing results showed that Sr addition improved the ultimate tensile and elongation of the Mg–6Zn–4Si alloys at both ambient temperature and 150 °C. Dry sliding wear tests indicated that the change trend of wear rate was basically coincident with that about the average size of the primary Mg₂Si phases. Optimal mechanical properties and wear behavior could be achieved by a Sr addition of 0.5%. An excessive Sr addition resulted in the formation of the needle-like SrMgSi compound, which was detrimental to the tensile properties and wear behavior of the alloys.     

Microstructure,tensile properties and creep behavior of Al-12Si-3.5Cu-2Ni-0.8Mg alloy produced by different casting technologies

The relationship between the as-cast microstructure and mechanical properties of the Al-12Si-3.5Cu-2Ni-0.8Mg alloys produced by permanent mold casting (PMC) and high pressure die casting (HPDC) is investigated. The alloys in both PMC and HPDC consist of Al, Si, Al₅Cu₂Mg₈Si₆, Al₃CuNi, and Al₇Cu₄Ni phase. However, the microstructure of the HPDC alloy is significantly refined. Compared to the PMC alloy, the ultimate tensile strength of the HPDC alloy is significantly increased from 244 MPa to 310 MPa, while the elongation shows a reverse trend at room temperature. At low stress and temperature range, slight variations of stress exponent and activation energy indicate that the minimum creep rate is controlled by the grain boundary creep. Then the minimum creep rate is higher for the specimen with the smaller grain size, where grain boundary creep is the dominant creep mechanism. At high stress region, the stress exponent for the PMC alloy and HPDC alloy is 5.18 and 3.07, respectively. The different stress exponents and activation energies measured at high stress and high temperature range indicates that the creep mechanism varies with the casting technologies.     

Microstructure and mechanical properties of Mg–8Li–xAl–0.5Ca alloys

The effect of the Al content on the microstructure and mechanical behaviour of Mg–8Li–xAl–0.5Ca alloys is investigated. The experimental results show that an as-cast Mg–8Li–0.5Ca alloy is mainly composed of α-Mg, β-Li and granular Mg₂Ca phases. With the addition of Al, the amount of α-Mg phase first increases and then decreases. In addition, the intermetallic compounds also obviously change. The microstructure of the test alloys is refined due to dynamic recrystallisation that occurs during extrusion. The mechanical properties of extruded alloys are much more desirable than the properties of as-cast alloys. The as-extruded Mg–8Li–6Al–0.5Ca alloy exhibits good comprehensive mechanical properties with an ultimate tensile strength of 251.2?MPa, a yield strength of 220.6?MPa and an elongation of 23.5%.     

Microstructural,mechanical and tribological properties of Al–7Si–(0–5)Zn alloys

A series of Al–7Si–(0–5)Zn alloys were produced by permanent mould casting and their microstructure, mechanical and tribological properties were investigated in as-cast state. The microstructure of Al–7Si alloy consisted of α-Al dendrites surrounded by eutectic Al–Si mixture and a small amount of primary silicon particles. Addition of zinc into Al–7Si alloy resulted in the formation of α-solid solution and an increase in size and volume fraction of primary silicon particles. Moreover, these particles gathered inside interdendritic regions of the ternary Al–7Si–Zn alloys. The density, strength and hardness of Al–7Si–Zn alloys increased continuously with increasing zinc content, but their elongation to fracture and impact energy showed a reverse trend. It was also observed that zinc had no significant effect on the friction coefficient of the alloys, but their wear volume decreased with increasing zinc content up to 4%, above which the trend reversed. The wear surfaces of the alloys were characterized mainly by smearing layer with some degree of oxidation. In addition, delamination and fine scratches were observed on the worn surface. It was concluded that the addition of zinc up to 4% improves both mechanical and wear behaviour of Al–7Si alloy.     

微量Sc和Zr对Al—Az—Mg合金组织与性能的影响

采用铸锭冶金法制备了Al-6.2Zn-2.0Mg-0.25Zr和Al-6.2Zn-2.0Mg合金,测试不同处理态的拉伸力学性能。利用金相显微镜和透射电子显微镜研究其不同处理态的显微组织,结果表明：添加微量Sc和Zr可明显细化合金的铸态晶粒,并显著提高Al-Zn-Mg合金的力学性能,其作用机理主要为Al3(Sc,Zr)造成的细晶强化,亚结构强化和弥散强化。