Zn添加对铸造Mg-Gd-Y-Zr合金组织和力学性能的影响（英文）

研究Zn添加对Mg-10Gd-3Y-0.6Zr(wt.%)合金在铸态、固溶态和峰时效态下显微组织和力学性能的影响。实验结果表明,不含Zn的铸态合金由α-Mg和Mg_(24)(Gd,Y)_5相组成,而含0.5wt.%Zn的铸态合金由α-Mg、(Mg,Zn)_3(Gd,Y)和Mg_(24)(Gd,Y,Zn)_5相组成。随着Zn含量增加到1 wt.%,Mg_(24)(Gd,Y,Zn)_5相消失,一些针状堆垛层错沿晶界分布。此外,在含2wt.%Zn的铸态合金中观察到18R型长周期结构相。固溶处理后,Mg_(24)(Gd,Y)_5和Mg_(24)(Gd,Y,Zn)_5共晶相完全溶解,(Mg,Zn)_3(Gd,Y)相、针状堆垛层错和18R型长周期结构相均转化为14H型长周期结构相。适当体积分数的14H型长周期结构相和细小的椭球状β′相共同赋予峰时效态下含0.5 wt.%Zn合金优良的综合力学性能,该合金的抗拉强度、屈服强度和伸长率分别为338 MPa、201 MPa和6.8%。     

热处理对Mg94Zn2Y4合金微观组织与力学性能的影响

研究了在773 K、48h 条件下热处理对Mg94Zn2Y4合金的微观组织与力学性能的影响。研究结果表明，块形和板条结构的18R 长周期堆垛结构相可直接从熔体凝固过程中形成。热处理后，绝大多数的块形和板条结构相转变为细片状或针状的14H相。在热处理过程中，有相当体积分数的 LPSO（长周期堆垛结构）相由 18R 转变为 14H。结果还表明，经过热处理，块形和板条结构相与针状相可以在 α-Mg 基体中共存，并作为影响因素，使合金晶粒得到细化，晶粒尺寸为14-24 μm（平均晶粒尺寸为19 μm），使极限拉伸强度、屈服强度以及伸长率分别由铸态时的 182 MPa、135 Mpa 和 10.2% 提高至 245 MPa、157 MPa 和 13.8%.     

热处理对Mg_(94)Zn_2Y_4合金微观组织与力学性能的影响（英文）

研究了在773 K、48 h条件下热处理对Mg_(94)Zn_2Y_4合金的微观组织与力学性能的影响。结果表明,块形和板条结构的18R长周期堆垛结构相可直接从熔体凝固过程中形成。热处理后,绝大多数的块形和板条结构相转变为细片状或针状的14H相。在热处理过程中,有相当体积分数的LPSO(长周期堆垛结构)相由18R转变为14H。结果表明,经过热处理,块形和板条结构相与针状相可以在α-Mg基体中共存,并作为影响因素,使合金晶粒得到细化,晶粒尺寸为14~24μm(平均晶粒尺寸为19μm),使极限抗拉强度、屈服强度以及伸长率分别由铸态时的182 MPa、135 MPa和10.2%提高至245 MPa、157 MPa和13.8%。     

LPSO堆垛结构转变对挤压态Mg-2.0Zn-0.3Zr-5.8Y镁合金组织性能的影响

通过改变挤压温度以获得含有不同堆垛结构长周期相(LPSO)的Mg-2.0Zn-0.3Zr-5.8Y合金,研究LPSO相堆垛结构转变对挤压态合金组织性能的影响规律及其作用机制。结果表明:挤压温度为390℃,合金中有18R和14H 2种堆垛结构的LPSO相,其平均晶粒尺寸为(9.5±3.0)μm,合金的抗拉强度达到280 MPa,延伸率为18.7%;当变形温度达到420℃,合金中18R LPSO相全部转变为14H结构,平均晶粒尺寸大幅细化至(3.1±1.1)μm,合金的抗拉强度和延伸率均得到明显提高,分别达到330 MPa和20.8%;随着挤压温度的进一步提高,合金的平均晶粒尺寸逐渐变大,强度和延伸率开始逐渐降低。由于LPSO相堆垛结构转变和晶粒尺寸变化引起基面织构和柱面织构的强度发生变化,LPSO相形态改变以及晶粒细化是Mg-2.0Zn-0.3Zr-5.8Y挤压态合金室温力学性能变化的主要因素。     

固溶处理对常规铸造Mg-Y-Zn-Ni合金显微组织的影响

通过OM、XRD、SEM和差热分析对Mg-Y-Zn-Ni合金的显微组织做了详细系统的研究。研究结果显示,随着合金中Ni含量的减少,18R长周期有序堆垛相的热稳定性逐渐降低,Ni被Zn取代后,长周期结构在固溶过程中逐渐溶解,同时镁基体晶粒内部析出一种新型的14H结构的长周期相。     

Cu-Al-Mn合金马氏体结构及其在时效过程中的变化

利用X射线衍射、透射电镜观察等方法研究了Cu 11 9Al 2 5Mn合金的马氏体结构及其在时效过程中的变化。该合金淬火态马氏体为单斜 18R结构 (M18R) ,点阵常数为 :a =0 4 4 75nm ,b =0 5 2 2 9nm ,c=3 815nm ,β =89 6°。特点是单斜角β很大 ,已非常接近正交 18R结构 (N18R) ;马氏体内存在两种类型的面缺陷 ,一种是基面堆垛层错 ,另一种是非基面堆垛层错 ;时效时马氏体由单斜向正交转变的过程在一定程度上受到抑制 ,因而具有较高的抗马氏体稳定化的能力。     

合金元素对铸态镁合金中长周期堆垛结构的形成与特征的影响

感应熔炼法制备了Mg97Y2M1(M=Zn,Ni,Ag)合金,运用TEM和SEM对铸态合金中的长周期堆垛结构(LPS)进行了分析.结果表明,铸态Mg97Y2Zn1中的LPS主要为6层周期堆垛,但不同于理想的6H型堆垛结构;在Mg97Y2Ni1中也存在LPS结构,与Mg97Y2Zn1相比,Mg97Y2Ni1中LPS具有较大的晶格畸变;Mg97Y2Ag1中未观察到LPS.结合实验结果,对影响LPS形成的因素进行了讨论.     

Zr(Cr,V)2 Laves相长周期堆垛结构的高分辨电子显微术观察

应用高分辨电子显微术对退火态Zr（Cr，V）2Laves相的显微结构进行了观察．结果表明退火态Zr（Cr，V）2Laves相在低倍显微观察下呈现层片状组织，并存在长周期堆垛结构；高分辨电镜和快速Fourier变换分析证明，退火态Zr（Cr，V）2长周期结构为C36（4H）结构，同时存在8H堆垛结构和少量其它过渡性多层堆垛结构、并就合金元素V对ZrCr2Laves相稳定性的影响进行了讨论．     

热轧Mg_(97)Zn_1Y_2合金板材组织和力学性能的研究

采用X射线衍射、扫描电子显微镜、透射电子显微镜和室温拉伸等方法,研究了总压下量分别为25%和50%的热轧Mg_(97)Zn_1Y_2(at%)合金板显微组织以及力学性能。结果表明:轧制过程中,具有14H长周期堆垛结构(LPSO)的Mg_(12)Zn Y相发生了扭折变形。随着轧制变形量的增大,LPSO相扭折变形程度增大。同时,轧制变形量较大的合金板材具有较强的基面织构,较高的抗拉强度和较好的塑性。     

热处理对Mg_(81)Ni_8Zn_5Y_6合金中长周期结构的影响

采用铜模铸造法制备直径为3 mm的Mg_(81)Ni_8Zn_5Y_6非晶复合材料,并分别在473和773 K条件下对材料等温热处理5 h。采用扫描电镜(SEM)、高分辨透射电子显微镜(HRTEM)、X射线衍射仪(XRD)等方法分别对铸态、热处理态复合材料的组织、相组成和结构进行分析,研究长周期(LPSO)相的热稳定性及不同长周期(LPSO)结构间的转化过程。结果表明:铸态Mg_(81)Ni_8Zn_5Y_6非晶复合材料的LPSO相为14H结构;473 K热处理5 h后,LPSO相转化为18R结构;773 K热处理5 h后,LPSO相转化为稳定的6H结构;成分和热处理温度均对长周期转化类型有影响。     

The 18R and 14H long-period stacking ordered structures in Mg–Y–Zn alloys

The 18R and 14H long-period stacking ordered structures formed in Mg–Y–Zn alloys are examined systematically using electron diffraction and high-angle annular dark-field scanning transmission electron microscopy. In contrast to that reported in previous studies, the 18R structure is demonstrated to have an ordered base-centred monoclinic lattice, with Y and Zn atoms having an ordered arrangement in the closely packed planes. Furthermore, the composition of 18R is suggested to be Mg₁₀Y₁Zn₁, instead of the Mg₁₂Y₁Zn₁ composition that is commonly accepted. The 14H structure is also ordered. It has a hexagonal unit cell; the ordered distribution of Y and Zn atoms in the unit cell is similar to that in the 18R and its composition is Mg₁₂Y₁Zn₁. The 18R unit cell has three ABCA-type building blocks arranged in the same shear direction, while the 14H unit cell has two ABCA-type building blocks arranged in opposite shear directions.     

含长周期堆垛有序结构Mg94Zn2Y4挤压态合金的显微组织与力学性能

采用SEM和TEM等分析方法研究包含长周期堆垛有序结构的挤压态Mg94Zn2Y4合金的显微组织和力学性能。结果表明：铸态Mg94Zn2Y4合金由18R-LPSO和α-Mg两相组成。挤压后,长周期相分层,并形成宽度为50~200 nm的α-Mg 薄片。合金经498 K时效处理36 h后达到时效峰值,在其组织中析出β′相,该析出相的出现显著提高了α-Mg基体的显微硬度,从HV108.9增加到HV129.7;而LPSO结构的显微硬度稳定在HV145左右。TEM分析及其电子衍射花样表明,β′相与α-Mg和LPSO结构具有独特的位相关系,其原子最密排面的堆垛方向垂直于α-Mg和LPSO相最密排面的堆垛方向。由于β′相和18R-LPSO相的共同存在,处于时效峰值态的Mg94Zn2Y4合金的抗拉强度达到410.7 MPa。     

Microstructure and mechanical properties of a compound reinforced Mg95Y2.5Zn2.5 alloy with long period stacking ordered phase and W phase

The microstructure evolution of Mg100-2xYxZnx(x=2, 2.5, 3, 3.5) alloys was investigated. Results show that the Mg100-2xYxZnx alloys are composed of α-Mg, long period stacking ordered(LPSO) phase and eutectic structure phase(W phase), and the Mg95Y2.5Zn2.5 alloy has the best comprehensive mechanical properties. Subsequently, the microstructure evolution of the optimized alloy Mg95Y2.5Zn2.5 during solidification and heat treatment processes was analyzed and discussed by means of OM, SEM, TEM, XRD and DTA. After heat treatment, the lamellar phase 14H-LPSO precipitated in α-Mg and W phase transforms into particle phase(MgYZn2). Due to the compound reinforcement effect of the particle phase and LPSO phase(18R+14H), the mechanical properties of the alloy are enhanced. The tensile strength and elongation of the Mg95Y2.5Zn2.5 alloy is improved by 9.1% and 31.3% to 215 MPa and 10.5%, respectively, after solid-solution treatment.     

Mg97Y2Zn1合金中18R型长周期有序相的微观结构（英文）

通过第一性原理计算研究Mg97Y2Zn1合金中18R型长周期有序相(LPSO)的微观结构,从理论上确定Zn和Y原子在LPSO相中的排列。结果表明:添加原子首先分布在18R型LPSO相两端的层错层,然后向内部的层错层延伸。计算结果与实验现象非常吻合。同时,也揭示了18R与其他LPSO相之间的微观结构关系;结合能和形成焓表明了18R型LPSO相的稳定性与Y和Zn原子含量之间的关系。计算得到的电子结构揭示了18R型LPSO相微观结构和稳定性潜在的机理。     

The structure of long period stacking/order Mg-Zn-RE phases with extended non-stoichiometry ranges

We propose structural models of the unique long period stacking/order (LPSO) phases formed in Mg-Zn-RE alloys, based on Z-contrast scanning transmission electron microscopy observations and first principles calculations. The LPSO structures are long period stacking derivatives of the hcp Mg structure, and the Zn/RE distributions are restricted at the four close-packed atomic layers forming local fcc stacking (i.e. a local ABCA stacking). Chemical order is well developed for the LPSO phases formed in Mg₉₇Zn₁Er₂ (14H type) and Mg₈₅Zn₆Y₉ (18R type) alloys with pronounced superlattice reflections, and the relevant Zn/RE distributions clearly emerge in the Z-contrast atomic images. Initial ternary ordered models were constructed by placing all the atoms at the ideal honeycomb sites, leading to plausible space groups of P6₃/mcm for the 14H type and C2/m, P3₁12 or P3₂12 for the 18R type. The characteristic ordered features are well represented by local Zn₆RE₈ clusters, which are embedded in the fcc stacking layers in accordance with the L1₂ type short-range order. Energy favored structural relaxations of the initial model cause significant displacement of the Zn/RE positions, implying that strong Zn-RE interactions may play a critical role in phase stability. The LPSO phases seem to tolerate a considerable degree of disorder at the Zn and RE sites with statistical co-occupations by Mg, extending the non-stoichiometric phase region bounded along the Zn/RE equiatomic line from ∼Mg_94.0Zn_2.0Y_4.0 to ∼Mg_83.3Zn_8.3Y_8.3.     

挤压比及不同Mn含量对Mg-10Gd-6Y-1.6Zn-xMn镁合金组织性能的影响

通过模铸法制备了Mg-10Gd-6Y-1.6Zn-xMn (x=0.4, 0.8, 1.2, 1.6, 2.0, wt.%)系列镁合金,研究了挤压比及Mn含量对Mg-10Gd-6Y-1.6Zn-xMn镁合金显微组织及室温力学性能的影响。研究结果表明：铸态Mg-10Gd-6Y-1.6Zn-xMn合金经热挤压后,合金中的长周期堆垛有序(LPSO)结构由亚稳的18R结构转变为稳定的14H结构。大挤压比能够显著提高合金的室温力学性能,当Mn含量为0.8%时,未时效态抗拉强度达到386MPa,断后延伸率约为10%。     

Controlling Corrosion Resistance of a Biodegradable Mg–Y–Zn Alloy with LPSO Phases via Multi-pass ECAP Process

Mg-RE(rear earth) alloys with long period stacking(LPSO) structures have great potential in biomedical applications. The present work focused on the microstructure and corrosion behaviors of Mg 98.5 Y_1 Zn_(0.5) alloys with 18 R LPSO structure after equal channel angular pressing(ECAP). The results showed that the ECAP process changed the grain size and the distribution of LPSO particles thus controlled the total corrosion rates of Mg 98.5 Y_1 Zn_(0.5) alloys. During the ECAP process from 0 p to 12 p, the grain size reduced from 160–180 μm(as-cast) to 6–8 μm(12 p). The LPSO structures became kinked(4 p), then started to be broken into smaller pieces(8 p), and at last comminuted to fine particles and redistributed uniformly inside the matrix(12 p). The improvement in the corrosion resistance for ECAP samples was obtained from 0 p to 8 p, with the corrosion rate reduced from 3.24 mm/year(0 p) to 2.35 mm/year(8 p) in simulated body fluid, and the 12 p ECAP alloy exhibited the highest corrosion rate of 4.54 mm/year.     

Investigation of two-phase Mg-Gd-Ni alloys with highly stable long period stacking ordered phases

The effects of the Ni addition on the microstructures of Mg-2Gd-xNi (at.%, x = 0, 0.25, 0.5 and 1) alloys were systematically investigated. A series of two-phase Mg-Gd-Ni alloys consisting of long period stacking ordered (LPSO) phase and α-Mg were obtained. The LPSO phase presented block-like shape and was distributed between α-Mg dendrite arms. Its volume fraction was found to be proportional to the Ni content, ranging from 0 to ∼40% with the Ni content increasing from 0 to 1 at.%. After a heat treatment at 500 °C for 100 h, the LPSO phase experienced a structure transformation from 18R to 14H but was hardly dissolved into the α-Mg matrix, which evidenced a high thermal stability. The mechanism for the effects of the Ni addition on the formation of the LPSO phase was discussed.     

Aging kinetics of 14H-LPSO precipitates in Mg-Zn-Y alloy

Alloys with long-period stacking ordered structures(LPSO)have good properties and are highly regarded.Mg-Zn-Y alloy containing LPSO phase was prepared by the traditional casting method,and the aging heat treatment was performed at different temperatures and times.The microstructure and phase constitutions of the alloy were observed by means of optical microscopy and scanning electron microscopy methods.Results show the microstructure of as-cast Mg95.5Zn1.5Y3 mainly consists ofα-Mg,W phases and LPSO phases.During the aging treatment,fine lamellar-shaped 14H-LPSO phase is formed at the grain boundaries and precipitates from the supersaturated magnesium matrix,and the volume fraction increases as the aging time increases.By controlling the aging time,Mg-Zn-Y alloys with different volume fractions of 14H-LPSO phase were prepared.The aging kinetics equation of the 14H-LPSO phase is summarized,that is f=1-exp(-0.2705 t 0.6368).The phase transformation mechanism of 14H-LPSO in Mg95.5Zn1.5Y3 alloy can be described as the change of dislocation energy.