Mg17Al12、Al2Y及Al2Ca相稳定性与弹性性能第一原理研究

采用基于密度泛函理论的Castep和Dmol程序软件包,计算了Mg17Al12、Al2Y及Al2Ca相的结构稳定性、弹性性能与电子结构。形成热和结合能计算结果表明:Al2Y具有最强的合金化形成能力和结构稳定性;热力学性质计算结果表明:在298~573 K温度范围内,Al2Y的Gibbs自由能始终最小,其结构热稳定性最好,Al2Ca次之,Mg17Al12最差,Y和Ca合金化Mg-Al系合金形成Al2Y及Al2Ca利于提高镁合金的高温抗蠕变性能;弹性常数的计算结果表明:3种金属间化合物均为脆性相,Mg17Al12的塑性最好;采用弹性常数计算结果预测的Al2Y熔点最高,其结构热稳定性最好。态密度和Mulliken电子占据数的计算结果表明:Al2Y结构最稳定的原因,主要源于体系在Fermi能级以下区域成键电子存在强烈的共价键作用。     

Mg-Al-Si-Ca合金系金属间化合物的电子结构和力学性能的第一性原理计算

采用基于密度泛函理论的第一性原理赝势平面波方法,计算了Mg-Al-Si-Ca合金系金属间化合物Mg2Si,Mg2Ca,Al2Ca以及Si2Ca四相的形成焓,结合能,弹性常数及态密度。形成焓和结合能的计算结果表明:Al2Ca的合金化能力最强,Si2Ca相的结构最稳定;体模量(B)、剪切模量(G)、杨氏模量(E)和泊松比(ν)的计算结果表明:四相均为脆性相,且Mg2Si相的塑性最差,结合弹性模量和态密度分析,得出Mg2Ca的塑性最好;态密度和Mulliken布居分析表明:四相中均存在离子键和共价键,共价键由强到弱顺序为Si2Ca,Al2Ca,Mg2Si,Mg2Ca;而离子键强弱顺序按Mg2Si,Al2Ca,Si2Ca,Mg2Ca依次递减;而Si2Ca最稳定的原因是其共价键比其他三相更强。     

热处理对ATX525镁合金中CaMgSn相形貌演化的影响

采用XRD、SEM和EDS研究了热处理温度对ATX525镁合金相组成、显微组织和析出相成分的影响,考察了保温时间为24 h条件下,Ca Mg Sn相随温度变化的演化规律。结果表明,合金组织中析出相由热稳定性较高的Mg2(Al,Ca)、Al2Ca和Ca Mg Sn等相组成。其中,Ca Mg Sn相中Sn和Ca含量随处理温度变化而变化,从而使其热稳定性和形貌发生变化。当温度低于500℃时,主要发生Ca Mg Sn溶断和破碎过程,体积分数没有显著变化;当温度为550℃时,Ca Mg Sn相发生溶入基体过程,体积分数减少;然而当处理温度为570~600℃,Ca Mg Sn相出现长大现象。获得细化Ca Mg Sn相貌的热处理温度为500~550℃。合金经过550℃/24 h处理后,经200℃/96 h时效,Ca Mg Sn相以条状和细小的颗粒状析出,与颗粒形貌相比,条状Ca Mg Sn相具有铸态时的形貌特征。     

喷射沉积Mg-4Al-3Ca-1.5Zn合金的显微组织

采用扫描电镜、透射电镜等方法对喷射沉积Mg-4Al-3Ca-1.5Zn合金的组织变化进行了试验研究.结果表明,金属型铸态合金中强化相沿晶界析出,主要成分为C36[(Mg,Al)2Ca]和C14(Mg2Ca)相;而喷射沉积快速凝固的合金组织均匀,强化相为C15(Al2Ca)和C36相,其中C15相以棒状和粒状分布于C36基体中;C36相处于亚稳态,经过高温保温处理会转变为C15相;热挤压过程中合金发生动态再结晶,在晶界处有C36相析出.     

Al-Sc金属间化合物的电子结构及稳定性和热力学性质

采用基于密度泛函理论的赝势平面波法,计算Al-Sc的4个稳定相的电子结构,分析其成键情况,并采用基于第一性原理的热力学计算公式,计算各相的生成焓、结合能、德拜温度、体弹模量和自由能。结果表明:Al-Sc金属间化合物在费米面以下,主要通过Al3s-Sc3d和Al3p-Sc3d杂化成键,在费米面以上则以Sc3d成键为主;随着Al在各相中所占比例的增大,体系中共价性增大,稳定性提高,且Al2Sc与Al3Sc在低能级区成键电子较多,结构较为稳定。在4个化合物中,0K时合金化形成能力最强的是Al2Sc(H0=-52.02kJ/mol),最弱的是AlSc2(H0=-35.93kJ/mol)。自由能计算所得曲线表明:Al2Sc的结构稳定性最好,AlSc2的最差;随着温度的升高,晶体稳定性都降低。所有热力学计算值与试验值吻合良好。     

Sn合金化MgZn_2相及Mg_2Sn相结构稳定性的第一原理研究

采用基于密度泛函理论CASTEP和DMol程序软件包,从合金形成热、结合能、热力学性能和电子结构等方面,研究Sn合金化MgZn2相及Mg2Sn相的结构稳定性,探讨Sn合金化改善ZA62镁合金抗蠕变性能的机理。结果表明:当Sn和Al分别置换ZA62镁合金中MgZn2相的Zn(Ⅰ)和Zn(II)原子时,仅Sn与Al置换的MgZn2相中Zn(Ⅰ)原子能形成稳定的MgZn2固溶体结构,而Sn在MgZn2相中的固溶量有限;与合金化形成的固溶体结构相比,其稳定性比未合金化时的弱,而析出的第二相金属间化合物Mg2Sn的结构比MgZn2的更稳定。而不同温度下热力学性能的计算结果表明:合金体系中形成了结构稳定性强的Mg2Sn,其结构稳定性在温度373～473K的范围内并不因温度的升高而消失,仍比MgZn2的高;由于ZA62镁合金体系中形成了高热稳定性的Mg2Sn相,Sn合金化有利于ZA62镁合金抗蠕变性能的提高。电子态密度和Mulliken电子占据数的分析结果表明:与MgZn2、Mg2AlZn3及Mg2SnZn3固溶体相比,热稳定性强的Mg2Sn相形成的主要原因在于Mg2Sn体系中存在强烈的离子键与共价键的共同作用。     

Mg17Al12相Ca合金化结构稳定性的第一原理研究

采用第一原理赝势平面波方法,计算了Mg17Al12相Ca合金化前后的能态与电子结构.计算结果显示:当Ca分别置换Mg17Al12相中Mg(Ⅰ)、Mg(Ⅱ)和Mg(Ⅲ)原子时,(Mg17-xCax)Al12相(x=0,1,4,12)的负生成热逐渐升高、结合能逐渐增大,表明Ca置换Mg17Al12相中Mg(Ⅲ)原子时其Ca合金化能力最强,合金化后形成的(Mg5Ca12)Al12相结构稳定性最高.电子态密度(DOS)分析结果表明:Ca合金化后Mg17Al12相结构稳定性升高的主要原因是由于合金化后来自Al(p)和Ca(s)的价电子使其在低能区的成键电子数增多.     

Sr、Ca复合添加对AZ31镁合金中合金相的影响

采用XRD、SEM和DSC等手段对Sr、Ca复合添加后的AZ31镁合金中合金相的类别进行了鉴别。结果表明,Ca与Mg元素在基体中形成了Mg2Ca合金相,并不是形成生成焓更低的Al2Ca。随着Ca含量的增加,基体中Mg2Ca合金相的含量增加,当Ca含量增加至0.6%(质量分数)时,基体中出现了带状析出相,并且在Mg2Ca合金相中发现了Sr元素的存在。利用合金相形核理论论证了基体中出现Mg2Ca而不是Al2Ca的原因,计算结果表明虽然Al2Ca的生成焓比较低,但是形核时产生的化学自由能变较大。且Al2Ca合金相的弹性模量与镁基体差异太大,其形核所产生的弹性应变能比Mg2Ca大,所以阻碍了Al2Ca在AZ31基体中形成。     

zA62镁合金中AB_2型金属间化合物的结构稳定性与弹性性能的第一原理计算

采用基于密度泛函理论Castep和Dmol程序软件包, 计算了ZA62镁合金中AB₂型金属间化合物 MgZn₂, Mg₂Sn和MgCu₂的结构稳定性、弹性性能与电子结构. 合金形成热和结合能的计算结果显示:  Mg₂Sn具有最强的合金化形成能力, 而MgCu₂结构最稳定; 体模量(B)、弹性各向异性系数(A)、Young's模量(E)、剪切模量(G)和Poisson比(ν)的计算结果表明: MgZn₂和MgCu₂为延性相, 而Mg₂Sn为脆性相, MgZn₂的塑性最好; 采用弹性常数、体模量和结合能的经验公式计算金属间化合物的熔点, 实验值均在采用弹性常数(±300 K)和体模量(±500 K)计算熔点预测的范围内, 采用弹性常数比采用体模量和结合能预测熔点的平均相对误差小, 其中采用弹性常数计算Mg₂Sn的熔点与对应的实验值十分接近, 相对误差仅为0.31%. 不同温度下热力学性质的计算结果表明, 在298-573 K温度范围内, MgCu₂的Gibbs自由能始终最小, 其结构热稳定性最好, 结构稳定性的强弱顺序并不随温度的升高而消失; 而对MgZn₂和Mg₂Sn, 以475 K为临界, 结构稳定性的强弱顺序随温度的升高发生了变化; 态密度和Mulliken电子占据数的计算结果表明: MgCu₂ 结构最稳定的原因主要在于体系在Fermi能级以下区域成键电子存在强烈的离子键作用.     

Al4Sr,Mg2Sr和Mg23Sr6相的电子结构与弹性性能的第一原理研究（英文）

采用第一性原理计算Al4Sr,Mg2Sr和Mg23Sr6相的电子结构与弹性性能。合金形成热与结合能的计算结果显示Al4Sr具有最强的合金化形成能力和最高的结构稳定性。通过计算弹性常数、体模量、剪切模量、弹性模量和泊松比,讨论了体系的韧性与塑性行为。结果表明,Al4Sr和Mg2Sr为延性相,Mg23Sr6为脆性相,在3种金属间化合物中,Mg2Sr的塑性最好。     

Structural stability of intermetallic compounds of Mg-Al-Ca alloy

A first-principles plane-wave pseudopotential method based on the density functional theory was used to investigate the energetic and electronic structures of intermetallic compounds of Mg-Al-Ca alloy, such as Al2Ca, Al4Ca and Mg2Ca. The negative formation heat, the cohesive energies and Gibbs energies of these compounds were estimated from the electronic structure calculations, and their structural stability was also analyzed. The results show that Al2Ca phase has the strongest alloying ability as well as the highest structural stability, next Al4Ca, finally Mg2Ca. After comparing the density of states of Al2Ca, Al4Ca and Mg2Ca phases, it is found that the highest structural stability of Al2Ca is attributed to an increase in the bonding electron numbers in lower energy range below Fermi level, which mainly originates from the contribution of valence electron numbers of Ca（s） and Ca（p） orbits, while the lowest structural stability of Mg2Ca is resulted from the least bonding electron numbers near Fermi level.     

Thermodynamic calculation of intermetallic compounds in AZ91 alloy containing calcium

1 Introduction Magnesium alloy is regarded as a promising structural material in the 21 century because of its excellent properties such as low density, high specific strength, good castability and machinability[1?5]. The common magnesium alloy AZ91 is, however, unsuitable for using at the temperatures above 120 ℃ because of its poor creep resistance and strength at elevated temperatures[2]. Adding other elements, like calcium, is an important method to improve the mechanical properties of A…     

镁合金表面新颖多层的耐腐蚀Mg-Al金属间化合物涂层(英文)

通过AlCl3-NaCl熔盐扩散表面改性,在镁合金表面制备多层的Mg-Al金属间化合物层。熔盐扩散的处理温度为400 °C,此温度低于纯铝粉扩散的处理温度。熔盐扩散处理后,在镁合金表面形成 Al12Mg17、Al0.58Mg0.42和Al3Mg2多相层的金属间化合物涂层。通过电化学阻抗实验将表面改性和未经表面改性的镁合金的耐蚀性进行比较,发现镁合金表面经过熔盐扩散处理的极化电阻远大于未经表面改性镁合金的。这是因为在镁合金表面形成均匀的多相金属间化合物层。     

Effect of HEA/Al composite interlayer on microstructure and mechanical property of Ti/Mg bimetal composite by solid-liquid compound casting

In this study,HEA/AI composite interlayer was used to fabricate Ti/Mg bimetal composites by solidliquid compound casting process.The Al layer was prepared on the surface of TC4 alloy by hot dipping,and the FeCoNiCr HEA layer was prepared by magnetron sputtering onto the Al layer.The influence of the HEA layer thickness and pouring temperature on interface evolution was investigated based on SEM observation and thermodynamic analysis.Results indicate that the sluggish diffusion effect of HEA can ...     

Effect of mischmetal and yttrium on microstructures and mechanical properties of Mg-Al alloy

The effect of yttrium and mischmetal(MMs)on the as-cast and solid solution treated structures of Mg-Al alloys with different Al-contents was investigated.The results show that the MMs in Mg-Al alloy existed in rod Al4(Ce,La)compound while Y in Mg-Al alloy in polygonal Al2Y compound.The amount of Mg17Al12 in Mg-Al alloy is decreased with increasing Y or MMs addition,and Mg17 Al12 intermetallic compound is changed from continuous network to discontinuous one.The Al4(Ce,La)and Al2Y compounds are not dissolved into Mg-Al alloy matrix during solid solution treatment so that their high heat stability can be exhibited.The experiment of mechanical properties indicate that elongation and impact toughness of the Mg-Al-Y alloy with polygonal Al2Y compound are higher than those of Mg-Al-MMs alloy with rod A4(Ce,La) compound.     

焊接温度对Mg/Al扩散焊接头微观组织和性能的影响

采用真空扩散焊在不同焊接温度下对AZ31B镁合金和6061铝合金进行连接。利用光学显微镜（OM）、扫描电镜（SEM）和能谱（EDX）观察Mg/Al异种金属接头的显微组织。结果表明：随着焊接温度的升高,扩散区各层的厚度增加,且组织发生明显变化。440°C时扩散层由Mg2Al3层和Mg17Al12层组成;460和480°C时由Mg2Al3层、Mg17Al12层和Mg17Al12与镁基固溶体的共晶层组成。随着加热温度的升高,高硬度区域显著增多,区域内不同位置的硬度存在明显差别。当焊接温度为440°C时接头的最大抗拉强度为37MPa,脆性断裂发生在Mg17Al12层。     

Novel multilayer Mg–Al intermetallic coating for corrosion protection of magnesium alloy by molten salts treatment

A novel multilayer Mg–Al intermetallic coating on the magnesium alloy was obtained by AlCl₃–NaCl molten salt bath treatment. The molten salt was treated at 400 °C, which is lower than the treatment temperature of solid diffusion Al powder. The thick Al₁₂Mg₁₇, Al_0.58Mg_0.42 and Al₃Mg₂ multilayer Mg–Al intermetallic coating forms on the magnesium alloy. The corrosion resistance of AZ91D alloy with and without coating by multilayer of Mg-Al intermetallic compound was evaluated by electrochemical impedance spectroscopy measurements in 3.5% (mass fraction) NaCl solution. The polarization resistance value of the multilayer coating on the magnesium alloy by molten salt bath treatment is greater than that of the uncoated one, which is attributed to the homogenously distributed intermetallic phases.     

Mg70Al20Ca10合金机械合金化过程中的结构变化

以纯金属Mg、Al和Ca为原料,采用机械合金化的方法制备了Mg70Al20Ca10非晶态合金,分析了球磨过程中粉末试样的晶粒尺寸变化和相结构变化情况.结果表明,球磨过程中形成纳米晶和两种非晶相.Mg-Al-Ca合金在化学驱动力较小的条件下,可以通过机械驱动力的作用提高Ca、Al在Mg中的固溶度,导致非晶转变的发生.     

Effect of Ca addition on microstructure and impression creep behavior of cast AZ61 magnesium alloy

Microstructure and creep properties of AZ61 alloy containing 1 and 3 wt.% Ca were investigated. The creep properties were examined using impression method under different stresses between 200 and 500 MPa at the temperature ranging from 423 to 491 K. The microstructure of AZ61 alloy contains α(Mg) matrix and Mg₁₇Al₁₂ intermetallic phases. It is shown that adding Ca to AZ61 alloy reduces the amount of Mg₁₇Al₁₂ phase via forming (Mg, Al)₂Ca phase; furthermore, increasing the Ca content to 3 wt.% leads to the formation of (Mg, Al)₂Ca phase, as well as the elimination of the Mg₁₇Al₁₂ phase. Creep properties of AZ61 alloy are improved with the Ca addition. The improvement in creep properties is attributed to the reduction in the amount of Mg₁₇Al₁₂ phase and the formation of (Mg, Al)₂Ca phase with high thermal stability. According to the obtained creep data, it is concluded that the pipe diffusion−climb controlled dislocation creep is the dominant creep mechanism and Ca addition has no influence on this mechanism. The effect of pre-deformation on the creep properties of AZ61+3%Ca alloy reveals that the creep resistance of the alloy depends on the continuity of (Mg, Al)₂Ca phase. It is decreased by reducing the phase continuity.