Effect of long-period stacking ordered phase on mechanical properties of Mg97Zn1Y2 extruded alloy

The mechanical properties of Mg97Zn1Y2 extruded alloy, composed of Mg matrix phase and a long-period stacking ordered phase, the so-called LPSO phase, with a volume fraction of approximately 24%, were investigated using compression tests at room temperature. The microstructure was varied to a large degree by various heat treatments at high temperatures above 400 °C, and the relationship between the microstructure and mechanical properties was clarified. The plastic behavior of the Mg/LPSO two-phase alloy was compared with that of Mg99.2Zn0.2Y0.6 alloy, composed almost Mg-solid-solution phase, and the strengthening mechanisms at work in the Mg97Zn1Y2 extruded alloy are discussed. The existence of the LPSO phase strongly enhanced the refinement of Mg matrix grains during extrusion, which led to a large increase in yield stress through the Hall–Petch relationship. In addition, the LPSO phases, which were aligned along the direction of extrusion in the Mg97Zn1Y2 extruded alloy, acted as hardening phases, being roughly coordinated with the short-fiber reinforcement mechanism.     

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。     

Ti含量对铸态Mg93Zn6Y1合金组织和力学性能的影响

采用光学显微镜、扫描电镜和X射线衍射仪等研究了Ti含量对铸态Mg93Zn6Y1合金凝固组织和力学性能的影响.结果 表明,添加Ti能够显著细化铸态合金的凝固组织.随着Ti含量的增加,合金中初生α-Mg相的晶粒尺寸先减小后增加,准晶相的形貌由连续网状转变为不连续网状,合金的抗拉强度和伸长率均先增加后降低.当添加0.4 at...     

Corrosion behavior of as-cast Mg68Zn28Y4 alloy with/-phase

Mg₆₈Zn₂₈Y₄ alloys with stable icosahedral quasicrystals (Zn₆₀Mg₃₀Y₁₀) were prepared by cast method. By simulating the environment of ocean, the alloy was eroded in 3.5% (mass fraction) NaCl for 2, 4 and 30 h. The microstructures of the samples and eroded alloys were analyzed by OM and SEM. The compositions and the quasiperiodic structures were identified respectively by EDS and TEM. And the corrosion potential and corrosion current density before and after immersion were measured by potentiodynamic polarization measurements in 3.5% NaCl. The results show that I-phases grow in the mode of conglomeration, piling and transfixion. The Mg₇Zn₃ matrix and α(Mg) solid solution are eroded badly, while W-phase is eroded partially. At the same time, the I-phases exhibit excellent corrosion resistance property. The resistance to corrosion of Mg₆₈Zn₂₈Y₄ alloy is improved by increasing exposed I-phases. With adding element Y to Mg₆₈Zn₃₂ alloy, the corrosion current is decreased by one order of magnitude. And after the immersion of as-cast Mg₆₈Zn₂₈Y₄ alloy for 30 h, the corrosion current density is reduced by two orders of magnitude compared with that of uneroded Mg₆₈Zn₃₂ alloy.     

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。     

Y对Mg-3Al-1Zn镁合金铸态组织的影响

研究Y对Mg-3Al-1Zn镁合金铸态组织的影响。结果表明,在Mg-3Al-1Zn合金中加入w(Y)=0.3%和w(Y)=0.6%对合金组织中合金相种类没有影响,但当w(Y)=0.9%时有Al3Y相存在。同时,加入微量Y使合金组织中Mg17Al12相基本上转变为断续状和颗粒状分布,且其分布具有一定方向性,同时其数量也逐渐减少。此外,研究结果还发现微量Y对Mg-3Al-1Zn合金的组织有一定的细化作用。     

钕添加及铸锭均匀化退火对ZK20镁合金组织与性能的影响

利用金相显微镜(OM)、扫描电镜(SEM)和万能材料试验机,对ZK20和ZK20+0.5Nd镁合金不同温度均匀化退火后的组织以及挤压态合金的力学性能进行研究。退火温度分别为603、633、663、693K,保温时间均为10h。结果表明:均匀化退火使铸锭中的Mg-Zn和Mg-Nd-Zn合金相不断固溶到基体中,同时枝晶偏析大幅度降低;与未均匀化相比,ZK20+0.5Nd合金均匀化退火后挤压,挤压态塑性有较大幅度提高,而强度并没有降低;稀土Nd细化ZK20合金晶粒,使均匀化退火提高挤压态合金塑性的作用更加明显,增强均匀化退火效果。对于ZK20合金,663K,10h是最优的均匀化退火工艺;对于ZK20+0.5Nd合金,693K,10h是较合适的退火工艺。     

稀土钇对铸态Mg-8Li-3Al-3Zn合金显微组织和力学性能的影响

镁锂(Mg-Li)合金是现今最轻的金属结构材料,在航空航天及交通运输等领域具有重大的应用价值.但铸造镁锂合金绝对强度低限制了其发展和应用.在Mg-Li二元合金中添加铝(Al)、锌(Zn)和稀土元素钇(Y)三种强化元素制备Mg-Li-Al-Zn-Y五元铸态镁锂合金来提高镁锂合金的力学性能.利用X射线衍射仪(XRD)、扫描...     

Effects of Cu addition on microstructure and mechanical properties of as-cast Mg-6Zn magnesium alloy

The application of Mg-Zn binary alloys is restricted due to their developed dendritic microstructure and poor mechanical properties. In this study, an alloying method was used to improve the mechanical properties of Mg-Zn alloy. The Mg-6Zn magnesium alloys microalloyed with varying Cu content(0, 0.8, 1.5, 2.0 and 2.5wt.%) were fabricated by permanent mould casting, and the effects of Cu content on the microstructure and mechanical properties of as-cast Mg-6Zn alloys were studied using OM, SEM, XRD and tensile tests at room temperature. The obtained results show that the addition of Cu not only can refine the grains effectively, but also can modify the eutectic morphology and improve the mechanical properties of the alloys. The main phases of the studied alloys include α-Mg, MgZn_2, Mg_2Cu and CuMgZn. When the content of Cu exceeds 0.8wt.%, Mg_2Cu phase appears. Meanwhile, the eutectic morphology is modified into dendritic shape or lamellar structure, which has an adverse effect on the tensile properties. Furthermore, among the investigated alloys, the alloy containing 0.8% Cu shows an optimalultimate tensile strength of 196 MPa, while the alloy with 1.5wt.% Cu obtains an excellent elongation of 7.22%. The experimental alloys under different Cu contents show distinguishing fracture behaviors: the fracture of the alloy with 0.8wt.% Cu reveals a mixed mode of inter-granular and quasi-cleavage, while in other investigated alloys, the fracture behaviors are dominated by cleavage fracture.     

Zn对铸态及ECAP态Mg15Al合金组织与性能的影响

采用XRD、SEM、EDS和拉伸试验,研究添加Zn元素前后铸态和等通道转角挤压(ECAP)态Mg15Al高铝镁合金的组织和力学性能。结果表明,Zn添加到Mg15Al合金中,主要固溶于β-Mg17Al12相,不生成新相。能够促进铸态Mg15Al合金中α-Mg晶粒细化,使β-Mg17Al12相质量分数增加,以及网状化加剧;使ECAP挤压后Mg15Al-1Zn合金中α-Mg基体晶粒平均尺寸由ECAP态Mg15Al合金的11.3μm减少到8.73μm,促进了β-Mg17Al12相的碎化和均匀分布;ECAP挤压能显著提高Mg15Al-1Zn和Mg15Al合金的综合力学性能,ECAP态Mg15Al-1Zn合金的抗拉强度较铸态合金提高了86%,ECAP态Mg15Al合金抗拉强度较铸态提高了60%,而且在屈服强度和塑性变化不大的情况下,ECAP态Mg15Al-1Zn合金比ECAP态Mg15Al合金室温抗拉强度提高了61.8MPa。说明Zn元素添加,能促进ECAP挤压对Mg15Al合金的晶粒细化效果,提高合金的综合力学性能。     

Effects of Pb on microstructure,mechanical properties and corrosion resistance of as-cast Mg97Zn1Y2 alloys

In this present work, Pb was applied in the Mg97Zn1Y2 alloy to improve its microstructure and properties, using conventional casting methods. The microstructure and properties of the Mg97 Zn1 Y2 alloy and Mg97Zn1Y2-x Pb(x=0.6 wt.%, 1.2 wt.% and 1.8 wt.%) alloys were observed by optical microscopy, scanning electron microscopy method and analyzed by X-ray diffraction, hardness and strength measurement and electrochemical testing. After adding Pb to the Mg97Zn1Y2 alloy, a new particle phase Mg_2 Pb was identified along the grain boundaries, and dendrites were refined. In addtion, the hardness of Mg97Zn1Y2-xPb(x=0.6 wt.%, 1.2 wt.% and 1.8 wt.%) alloys was higher than that of the Mg97 Zn1Y2 alloy; with the increase of Pb content, the hardness of the alloy increased first and then decreased, followed by a final slight increase, and reached a maximum of 89.1 HV when the Pb content was 0.6 wt.%. The strength of the alloy increased first and then decreased as the Pb content increased. Moreover, adding a small amount of Pb to the alloy can effectively inhibit corrosion, and Mg97Zn1Y2-0.6 wt.%Pb exhibits the best corrosion resistance ability.     

Microstructural evolution and mechanical properties of Mg95.5Y3Zn1.5 alloy processed by extrusion and ECAP

A Mg_95.5Y₃Zn_1.5 alloy processed via a two-step processing route of extrusion plus ECAP has been investigated. It was found that the ECAP processed Mg_95.5Y₃Zn_1.5 alloy contained ultrafine grains and exhibited excellent mechanical properties. After ECAP, the average grain size of Mg_95.5Y₃Zn_1.5 alloy was refined to about 300 nm. The highest strengths, with yield strength of 444.6 MPa and ultimate tensile strength of 472.7 MPa, were obtained after 1 pass at 623 K. The SAED patterns indicated that the microstructure after ECAP consisted of both high angle and low angle grain boundaries. The fraction of high-angle boundaries increased with increasing numbers of ECAP passes. The Mg_95.5Y₃Zn_1.5 alloy contained a high volume fraction of X-Mg₁₂ZnY phase due to high yttrium and zinc addition. And, it accelerated the growth and coalescence of cracks during tensile testing, resulting in premature fracture and lower elongation of alloy.     

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%.     

Effect of Mg24Y5 intermetallic particles on grain refinement of Mg-9Li alloy

The microstructures of the as-cast and as-extruded Mg-9Li-xY alloys (x = 0, 0.3; wt%) were observed to investigate the effect of Y on the Mg-9Li alloy, and the crystallographic calculations between Mg₂₄Y₅ and the matrix were examined on the basis of the edge-to-edge matching model. The results indicated that with the addition of 0.3 wt% Y, the average grain size of α-Mg phases in the as-cast Mg-9Li alloy and β-Li phases in the as-extruded Mg-9Li alloy were reduced remarkably, which was caused by the formation of Mg₂₄Y₅ intermetallic compound. Furthermore, crystallographic calculations confirmed that Mg₂₄Y₅ particles were effective grain refiners for both α-Mg and β-Li phases in Mg-9Li alloy.