Y对普通凝固Mg-Zn-Y系合金组织及准晶相形成的影响

采用普通凝固技术在高镁、低锌和低钇合金中制备出镁合金稳定态准晶相，为制备准晶增强自生复合材料的可行性开辟途径。通过光学显微镜、X—ray衍射、扫描和透射电镜显微分析技术，确定了准晶的组织、相成分及结构。分析了由于合金成分小同，特别是稀土元素Y摩尔分数的不同导致准晶的分布、数量等差异。结果表明：Mg-Zn-Y三元合金在室温冷却过程中，准品相直接从液相形核、长大；伴随Y摩尔分数的增加，准晶相的晶粒度、圆整度和分布均匀化程度均有提高。     

Al65Cu20Fe15合金的凝固组织及二十面体准晶的生成

用Ｘ射线能谱分析、电子背散射衍射和粉末Ｘ射线衍射等技术研究了Ａｌ６５Ｃｕ２０Ｆｅ１５合金的铸锭及其退火后的显微组织和相组成。发现铸锭中的初生晶是λ－（Ａｌ,Ｃｕ）１３Ｆｅ４,呈明显的枝晶结构。     

Mg-Zn-Y三元合金富Mg区凝固组织及二十面体准晶相形貌

通过常规凝固方法在Mg28Zn2Y三元合金中的富Mg区获得了二十面体稳定准晶相。Mg28Zn2Y三元合金铸态组织中存在α-Mg相，Mg7Zn3相和二十面体准晶相。该合金的准晶形貌有两种：一种为尺寸较大、具有五次对称性的花瓣状；另一种为尺寸稍小、对称性不太明显的团状。五次对称性的花瓣状形貌是二十面体准晶，是按其特有的五次对称轴的择优方向自由生长所致。冷却速率直接影响合金凝固过程中准晶熟化时间。熟化时间越长，越容易使准晶花瓣端部粗化以及在端部发生分又。端部的分叉容易使得花瓣准晶破碎，破碎的准晶游离到低温相中，在界面能的作用下形成多边形形貌。     

含二十面体准晶相Mg-Zn-Y合金的组织和性能

采用常规凝固技术制备了MgZn_6xY_x(x=0.7,1.0,1.5,2.0)合金,研究了Y含量对含有二十面体准晶相(I相)MgZn_6xY_x合金组织和性能的影响。结果表明,MgZn6xYx合金由α-Mg基体和分布在晶界周围的(α-Mg+I相)共晶组织组成。随着Y含量增加,基体晶粒尺寸减小,共晶组织尺寸增大,含量增加,由不连续分布转变为连续分布。在凝固过程中,二十面体准晶相通过共晶转变形成。Mg_89.5Zn_9.0Y_1.5合金的抗拉强度和伸长率达到最大值,分别为179.2MPa和3.5%。MgZn_6xY_x合金的断口呈现准解理断裂特征。     

Mg-Zn-Y三元合金中二十面体准晶相生长形貌及其演化

采用常规凝固方法在Mg-Zn-Y三元合金系中获得了大体积分数的二十面体准晶。二十面体准晶相有2种典型形貌特征：一种为花瓣状，另一种为多边形形状。这是准晶在生长过程中形貌演化的结果。合金的成分和冷却速率是影响准晶形貌的主要岗素。准晶合金中生成的低温相越多，冷却速率越慢，准晶相生长的时间和空间条件越好，准晶相越容易由花瓣状演化成多边形状。准晶的形成有包晶反应参与，包晶反应是一种由初生固态相扩散控制的反应，因此，准晶在生长初期和最终形态其元素含量有明显差别，分析表明，准晶生长初期Mg元素含量偏低，Zn和Y元素含量偏高。     

Mg70Zn28Y2合金凝固过程、凝固组织及包晶反应初生相研究

采用XRD，SEM，EDX，TEM，DTA等试验分析手段及快淬方法对MgToZn28Y2准晶合金凝固过程、凝固组织以及对和准晶形成相关的包晶反应初生相进行了研究。Mg70Zn28Y2合金铸态组织由α-Mg枝晶，Mg7Zn3基体相和二十面体准晶相组成。在铸态Mg-Zn-Y合金中观察到了完美的呈5次旋转对称性的平衡态准晶晶体外形。Mg70Zn28Y2合金凝固过程中准晶由包晶反应生成。差热分析显示包晶反应初生相在563℃形成，准晶形成的温度为416℃。能谱分析结果显示包晶反应初生相的成分为Mg22.94Zn55.73Y21.33。通过快淬方法保留的包晶反应初生相呈现粗大枝晶状。然而，通过背散射图片中所观察到准晶中的残留包晶初生相尺寸较小。     

Mg30Zn60Y10合金中二十面体准晶相的形成和生长

通过常规凝固方法在Mg30Zn60Y10三元合金中获得大体积分数准晶。准晶相由包晶反应生成。能谱分析结果表明包晶反应中初生相的成分近似为Mg16.32Zn70.60Y13.08，准晶相成分为Mg36.94Zn56.21Y6.63。差热分析显示初生相在723℃形成，准晶相生成温度为648℃。利用快淬方法使准晶相生长初期形貌得以保留，发现准晶相初期形貌受初生相形貌直接影响，但随后则接其晶体学优先方向生长，最终长成花瓣状准晶。准晶合金凝固过程中生成的低温相越多，准晶相熟化时间越长，越容易使准晶花瓣端部粗化以及在端部发生分叉。端部的分叉使得花瓣准晶破碎，这些破碎的准晶游离到低温相中在界面能的作用下形成多边形结构。     

塑性变形对Zr-Al-Ni-Cu-Ag非晶合金中二十面体准晶相析出的影响

利用x射线衍射(XRD)和差示扫描量热法(DSC)研究了轧制对Zr65Al7.5Ni10Cu12.5Ag5非晶合金中二十面体准晶相析出的影响.实验发现,经轧制塑性变形合金在随后的加热过程中二十面体准晶相的析出量增加,在变形量ε=70%时达到最大.另外,析出的二十面体准晶相的稳定性随着变形量增大而提高,在ε=70%时达到最大,随后又开始降低.这是由于合金在塑性变形过程中的原子组态发生变化所致.     

Mg30Zn60Y10合金中二十面体准晶相的生长及形态演化

利用楔形铜模具激冷浇注方法和SEM、XRD、DTA、TEM等分析手段,研究了Mg30Zn60Y10合金中二十面体准晶相(I-相)的形成过程和不同冷速下该合金的凝固组织.研究结果表明,在中等冷速下,I-相主要以初生相与剩余液相发生包晶反应形成.随着冷速的增大,I-相的生长形貌将由棱面状向枝晶状转变.当冷速大到一定程度时发生初生相的相选择.在利用DTA分析I-相的形成温度时发现,包晶反应即I-相开始形成的温度受分析时采用的温度变化速率影响.     

Mn对Mg—Zn—Y合金中准晶相凝固组织形貌的影响

讨论了Mn对镁基准晶中间合金中三维二十面体球形准晶相形成过程的影响。研究表明：当在Mg-Zn-Y基准晶中间合金熔体中加入一定量的Mn元素后，在常规铸造条件下的结晶凝固过程中，完全可以改变Mg-Zn-Y基准晶中间合金中准晶的形成过程，获得稳定的均一二十面体初生Mg45Zn47Y5Mn3准晶相，避免了十面体准晶相的出现，改变了准晶相最终的形貌，由于Mn的加入，使初生准晶相的颗粒尺寸明显变小，使之由尺寸为60gm～80gm的花瓣状变成尺寸为≤20gm的球形状。Mn的加入，降低了镁基准晶中间合金的生产成本，为工业化生产提供了便利条件。     

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.     

Icosahedral quasicrystalline phase in an as-cast Mg-Zn-Er alloy

The microstructure of an as-cast Mg-Zn-Er alloy was investigated through scanning electron microscopy (SEM) and transmission electron microscopy (TEM) equipped with energy dispersive spectroscopy (EDS). The results indicate that two different second phases, one with eutectoid-lamellar morphology and the other with granular shape, distribute in the α-Mg matrix. The coexistence of the face-centered icosahedral quasicrystalline phase (I-phase) and W-phase with the face-centered cubic structure is found in the as-cast alloy. The coexistence of I-phase and W-phasc in the Mg-Zn-Er alloy is because the W-phase is the primary phase and the I-phase forms by peritectic reaction during solidification.     

Solidification of Mg-28%Zn-2%Y alloy involving icosahedral quasicrystal phase

Applying XRD, DTA, SEM and TEM techniques, an investigation on the solidification microstructure and solidification sequence of Mg-rich Mg-28%Zn-2%Y （mole fraction） alloy was carried out. It is found that, a-Mg dendrites, Mg7Zn3 phase and icosahedral quasicrystal phase coexist in the as-solidified alloy, where the icosahedral quasicrystal, whose structure is indentified to be a face-centered type, originates from a peritectic reaction occurring at 416 ℃. The primary phase of this peritectic reaction has the composition of Mg20Zn66Y14, which is coincident with the H phase reported by TSAI as （Zn, Mg）5Y. Furthermore, the single I-phase grain morphology was observed and its growth evolution was also discussed.     

Microstructure Formation and Mechanical Property Involving Icosahedral Quasicrystal Phase of Y Rich Mg-Zn-Y Quasicrystal Alloy

The microstructure formation and mechanical property involving icosahedral quasicrystal (I-phase) in the Y-rich Mg-Zn-Y alloy have been studied. The equilibrium formation of I-phase from the Y-rich Mg-Zn-Y melt is through a peritectic reaction between the Y-rich melt and the primary W-phase, which is discussed in detail. The independent nucleation and coupling growth mechanism between the W-phase and the I-phase, from the melt, are revealed, which is significant for understanding the peritectic reaction process involving icosahedral quasicrystal in the Mg-Zn-Y alloy. The mechanism of the quasicrystal phase strengthened magnesium alloys is also discussed here.     

Amorphous in a Zr-IQC-DQC pseudo-ternary alloy system

A pseudo-ternary alloy system was constructed by combining an icosahedral quasicrystal (IQC), a decagonal quasicrystal(DQC), and Zr into one alloy system. Different proportions of Zr were added to pseudo-binary alloy IQC80DQC20 (mass fraction in %). Structural evolution in these alloys was discussed. An amorphous alloy composition was found in this system and a melt-spinning amorphous alloy was produced in this composition. Through DSC analysis, the amorphous alloy exhibits high glass forming ability comparable to that of the Inoue Zr65Al75Cu17.5Ni10 amorphous alloy.     

Effect of hot extrusion on microstructure and mechanical properties of quasicrystal-reinforced Mg-Zn-Y alloy

The microstructure and mechanical properties of as-cast and as-extruded Mg-Zn-Y alloy （Mg-11 %Zn- 0.9%Y, mass fraction） containing Mg3 YZn6 quasicrystal were studied. The eutectic icosahedral quasicrystal phase （I-phase） is broken and almost distributes along the extrusion direction, and fine I-phase with nano-size is precipitated during the extrusion. The a-Mg matrix grains are refined due to recrystallization occuring during the hot extrusion. Some {1012} twins are observed in the extruded ZW1101 alloy. And {0002}（1010） fiber texture is formed in matrix alloys after hot extrusion. The extruded alloy exhibits high strength in combination with large elongation at room temperature. The strengthening mechanism of the as-extruded alloy was discussed.     

Y对常规凝固Mg-Zn-Y合金组织和性能的影响

采用常规凝固技术制备了Mg-45Zn-xY(x=1.0,4.0,5.5,8.0,质量分数,%)合金。利用SEM、EDS、OM、TEM、XRD、DSC和硬度测试技术研究了Y对Mg-45Zn-xY系合金组织及性能的影响,同时对准晶相(I-phase)的形成机制进行了分析。结果表明:合金组织主要由α-Mg颗粒或枝晶、花瓣状的Mg3Zn6Y准晶相、层片状的(I-phase+α-Mg)共晶组织以及Mg7Zn3相组成;准晶相形貌、含量及分布与Y含量密切相关,随着Y含量的增加,花瓣状准晶相含量逐渐增加,当Y含量为5.5%时,花瓣状准晶相含量最多,合金的硬度达到最大值,HB为1557 MPa,当Y含量为8.0%时,合金中的花瓣状准晶相消失;准晶以层片状共晶组织和花瓣状形式存在,花瓣状的特殊形貌是正二十面体沿五次轴方向生长的结果。