稀土元素对镁合金力学行为影响的研究现状

系统论述了不同稀土元素的结构特性,基于镁合金的强化机制,并结合当前稀土镁合金的研究现状,展示了稀土元素的添加对镁合金在强度、塑性及抗蠕变性能等方面带来的变化,尤其是对镁合金塑性的影响.其中,区别于传统的强化机制,对添加稀土元素后出现的LPSO结构相对镁合金性能的影响也进行了重点讨论,进一步对镁合金中的稀土元素合金化后的改性作用及前景进行了探讨和展望.     

相变温度附近等温热处理对Mg97Zn1Y2合金组织演化的影响

研究了相变温度附近等温热处理温度和保温时间对含长周期结构Mg97Zn1Y2合金的组织的影响，并对演变机理进行了探讨。主要研究结论如下：500℃固溶处理时，随着时间的增加，长周期结构有增长的趋势。采用等温热处理可以将Mg97Zn1Y2合金中的枝晶组织转变为球状晶，当合金保温温度范围从540℃~600℃时，组织尺寸由大-小-大的顺序变化，即经过了粗化、分离及球化至最后粗化三个过程。在等温热处理温度为575℃的组织大致演变趋势为：枝晶态-不规则球形+块状-球形状，当保温时间15min，其组织为均匀、圆整的球状晶。     

Effects of Zn and Y on hot-tearing susceptibility of Mg–xZn–2xY alloys

The effect of Zn and Y on hot-tearing susceptibility (HTS) of Mg–xZn–2xY (x?=?1, 1.67, 2.67) alloys is investigated. It is found that the microstructure of the alloys is mainly composed of α-Mg, long-period stacking-ordered (LPSO) phase and W-phase. Both theoretical and experimental results illustrated that HTS of the investigated alloys is in the following order: Mg–1Zn–2Y > Mg–1.67Zn–3.34Y > Mg–2.67Zn–5.34Y. For Mg–2.67Zn–5.34Y alloy, LPSO phase content reaches at the maximum and its grain size reaches at minimum of 16.4 µm, and the pinning effect of the LPSO phase on grain boundaries is considered to be an important reason for reducing HTS of the alloy.     

超声振动对含LPSO结构的Mg98Y1.0Ni0.5Al0.5合金显微组织与力学性能的影响(英文)

低Y、Ni含量的LPSO结构增强镁合金具有低成本、优异力学性能的特点。为进一步提升其综合力学性能,掺杂Al元素及熔体超声振动处理是可行的途径。通过扫描电子显微镜、能谱分析、透射电子显微镜、X射线衍射和纳米压痕测试研究掺杂Al元素后低Y、Ni含量的Mg98Y1.0Ni0.5Al0.5合金的显微组织,对比超声振动对显微组织与力学性能的影响。掺杂Al后LPSO结构的含量降低,且在块状LPSO结构相邻处析出圆整的Al₂NiY相。Al₂NiY相与LPSO结构和Mg基体在界面处均不共格。通过对熔体施加超声振动处理后,Al₂NiY相被有效细化为短片状,并均匀分布在基体中,阻碍微裂纹的产生和扩展,从而提高Mg₉₈Ni_0.5Y_1.0Al_0.5合金的力学性能。与未经超声处理Mg₉₈Ni_0.5Y_1.0Al_0.5合金相比,其极限抗拉强度和伸长率提升至187 MPa和7.9...     

Precipitate evolution in Mg−7Gd−3Y−1Nd−1Zn−0.5Zr alloy during isothermal ageing at 240 °C

The morphology and crystal structure of the precipitates in Mg−7Gd−3Y−1Nd−1Zn−0.5Zr alloy during isothermal ageing at 240 °C were investigated using transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). After under-ageing for 2 h, the precipitates in the alloy are ordered solute clusters with rare earth atomic columns exhibiting hexagonal ring structure, zigzag GP zones and β' in its early formation. After peak-ageing for 18 h, the precipitates are mainly β' and new rod-like β'_p accompanied with β'. After over-ageing for 100 h, the precipitates are β', β₁, long-period stacking ordered (LPSO) building block known as γ′ and 14H-LPSO. β' has the three-dimensional shape of convex lens with smaller length-to-width ratio viewed along 〈0001〉_α than that in the EW75 alloy. The excellent thermal stability of this alloy can be attributed to the γ' and 14H-LPSO retarding the growth of β' and β₁, low diffusion rate of rare earth atoms and physical character of β' and β₁.     

具有长周期结构的Mg–Gd–Zn–Zr合金的微结构和摩擦学行为

利用传统的熔铸法制备Mg-14.28Gd-2.44Zn-0.54Zr合金,研究铸态和固溶态合金的微结构。利用销-盘装置研究铸态和固溶态合金的室温润滑滑动摩擦磨损行为研究。在外载荷为40 N,滑动速度为30-300 mm/s以及滑行路程为5000 m情况下,测量磨损率和摩擦因数。研究结果表明：铸态合金主要由α-Mg固溶体、分布在基体内的层片状的14H型长周期结构（LPSO）和β-[（Mg,Zn）3Gd]相组成。经过温度为773 K固溶处理35 h后,大量的β相转变成具有14H型X相LPSO结构。由于固溶处理后大量β相转变为热稳定的韧性X-Mg12Gd Zn长周期结构相,固溶合金呈现较低的抗磨损能力。     

Microstructure and phase composition of as-cast Mg–9Er–6Y–xZn–0.6Zr alloys

The microstructure and phase composition of as-cast Mg–9Er–6Y–xZn–0.6Zr (x=1, 2, 3, 4; normal mass fraction in %) alloys were investigated. In low Zn content, aside from the major second phase of Mg₂₄(Er, Y, Zn)₅, there are a few lamellar phases that grow parallel with each other from the grain boundaries to the grain interior. With Zn content increasing, the Mg₂₄(Er,Y,Zn)₅ phase decreases, but the Mg₁₂Zn(Y, Er) phase and lamellar phases continuously increase. When Zn content reaches 4% (normal mass fraction), the Mg₁₂Zn(Y,Er) phase mainly exists as large bulks, and some α-Mg grains are thoroughly penetrated by the lamellar phases. Moreover, the crystallography structures of the Mg₁₂Zn(Y,Er) and Mg₂₄(Er,Y,Zn)₅ phases are confirmed as 18R-type long-period stacking ordered structure and body-centred cubic structure, respectively.     

Hydrogen storage properties of Mg98.5Gd1Zn0.5 and Mg98.5Gd0.5Y0.5Zn0.5 alloys containing LPSO phases

In this work, the as-cast Mg-rich Mg_98.5Gd₁Zn_0.5 and Mg_98.5Gd_0.5Y_0.5Zn_0.5 alloys are prepared by the semi-continuous casting method, and their hydrogen storage performance and catalytic mechanisms are investigated by experimental and first-principles calculations approaches. The results show that the LPSO phases decompose and in-situ form the RE(Gd/Y)H_x(x = 2,3) nano-hydrides upon hydrogenation. These nano-hydrides not only serve as the in-situ catalysts to promote the hydrogen ab/desorption of Mg matrix, but also present the pinning effect to inhibit the growth of Mg/MgH₂ grains during hydrogenation and dehydrogenation. Comparatively, the two alloys exhibit the similar hydrogen absorption kinetics, while the hydrogen desorption kinetics of Mg_98.5Gd₁Zn_0.5 is superior to that of Mg_98.5Gd_0.5Y_0.5Zn_0.5. The first-principles calculations reveal that the GdH₂ and YH₂ hydrides exhibit different catalytic effects on weakening the bond strength of H–H within H₂ and Mg–H within MgH₂, which interprets well the differences in the hydrogen ab/desorption kinetics between Mg_98.5Gd₁Zn_0.5 and Mg_98.5Gd_0.5Y_0.5Zn_0.5 alloys.     

A 12R long-period stacking-ordered structure in a Mg-Ni-Y alloy

A hitherto unreported long-period stacking-ordered (LPSO) phase, designated 12R, was observed in a Mg₈₀Ni₅Y₁₅ (at.%) alloy. Microstructure was investigated by electron diffraction and high-angle annular dark-field scanning transmission electron microscopy. Results show that the 12R has a trigonal lattice (a = b = 1.112 nm, c = 3.126 nm, α = β = 90°, and γ = 120°). Unit cell of the 12R is consisted of three ABCA-type building blocks and each building block contains dominant Ni₆Y₈-type building clusters. A sound structural model is proposed based on relative positions of Ni₆Y₈ clusters in neighboring building blocks.     

热处理对GWZK94合金微观组织与力学性能的影响

为了改善铸态GWZK94合金微观组织的不均匀性,使用电阻加热炉在温度505-520 ℃范围内保温8-20 h进行热处理实验。本文采用光学显微镜（OM）,差示扫描量热仪（DSC）,X射线衍射仪（XRD）,扫描电子显微镜（SEM）,能谱仪（EDS）,电子背散射衍射技术（EBSD）,万能试验机和维氏硬度计进行微观组织演变及力学性能分析。铸态合金组织主要包括树枝状α-Mg基体,包含亚稳态层错（SFs）的片层结构,共晶相Mg24(Gd, Y, Zn)5,块状长周期有序堆垛结构(LPSO, Mg12(Gd, Y) Zn)和少量的富稀土相。在均匀化处理过程中,片层结构和共晶相Mg24(Gd, Y, Zn)5逐渐溶于基体中,同时块状LPSO相体积分数逐渐减小并伴随有片层状LPSO相像晶粒内部生长,颗粒状相在晶界附近析出。加热温度为520 ℃时出现复熔三角晶界,说明此时发生了合金的过烧现象。经过均匀化处理后,合金的极限抗拉强度（UTS）和合金屈服强度（TYS）表现出了与组织演变规律相同的变化趋势,同属得到了较为均匀的硬度分布情况。最佳的均匀化制度为515 ℃/16 h.