Effects of heat treatment on microstructure evolution and mechanical properties of Mg-6Zn-1.4Y-0.6Zr alloy

To investigate the effects of solution temperature and the decomposition of I-phase on the microstructure, phase composition and mechanical properties of as-cast Mg-6Zn-1.4Y-0.6Zr alloy, solution treatment at 440 oC, 460 oC and 480 oC and further aging treatment were conducted on the alloy. The results indicate that the net-like intermetallic compounds(mainly I-phase) dissolve into the α-Mg matrix gradually with the increase of solution temperature from 440 oC to 480 oC. Besides, the I-phase decomposes completely at 480 oC, with the formation of fine W-phase(thermal stable phase) and Mg_7Zn_3 phase. In addition, a great number of fine and dispersive Mg-Zn binary phases precipitate in the α-Mg matrix during the aging treatment. Due to the increase of solute atoms and the precipitation of strengthening phases, such as W-phase and Mg-Zn phases, the optimal strength is obtained after solution treatment at 460 oC for 8 h and aged at 200 oC for 16 h. The yield strength(YS), ultimate tensile strength(UTS) and elongation are 208 MPa, 257 MPa and 3.8%, respectively. Compared with the as-cast alloy, the increments of YS and UTS are 117% and 58%, respectively, while the decrement of elongation is 46%.     

Influence of Zn Content on Microstructure and Tensile Properties of Mg–Zn–Y–Nd Alloy

In the present study, the effect of Zn content on the microstructure and deformation behavior of the as-cast Mg–Zn–Y–Nd alloy has been investigated. The results showed that as Zn content increased, the volume fraction of secondary phases increased. Moreover, the phase transformation from W-phase to W-phase and I-phase occurred. In the as-cast state,W-phase exists as eutectic and large block form. When Zn content increases to 6 and 8%(wt%), small I-phase could precipitate around W-phase particles. Additionally, the effect of Zn content on the tensile properties and deformation behavior varies with the testing temperature. At room temperature, the tensile strength increases with Zn content, whereas the elongation increases initially and then decreases. At 250 °C, as Zn content increases, the tensile strength decreases initially and then increases slightly, whereas the elongation decreases. At 350 °C, the elongation increases with Zn content,whereas the tensile strength decreases initially and then increases slightly.     

热处理对Mg-5Zn-0.63Er合金显微组织及力学性能的影响

通过不同的热处理工艺研究含有准晶Ⅰ相的铸态Mg-5Zn-0.63Er(质量分数,％)合金的显微组织演变.结果表明:合金在480℃固溶10 h后,除有W相颗粒析出外,准晶Ⅰ相几乎全部固溶在基体中.固溶态Mg-5Zn-0.63Er合金在175℃下时效6～10h.合金在峰时效态的抗拉强度约为261MPa、伸长率为10.5％.合金拉伸强度的提高归因于杆状MgZn2相的析出.     

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.     

Effect of Phase Transformation During Long-Term Solution Treatment on Microstructure,Mechanical Properties,and Bio-corrosion Behavior of Mg–5Zn–1.5Y Cast Alloy

The influence of long-term solution treatment for various intervals on the microstructure,mechanical properties,and corrosion resistance of the as-cast Mg–5Zn–1.5Y alloy was investigated.Variation of secondary phases was studied during solution treatment through thermal analysis test and thermodynamic calculations.Tensile and hardness tests,as well as polarization and immersion tests,were performed to evaluate the mechanical properties and corrosion behavior of the ascast and heat-treated alloy,respectively.Results show that solution treatment transforms I-phaseinto W-phaseas well as dissolves it into the a-Mg matrix to some extent;therefore,the amount of W-phase increases.Moreover,prolonged solution treatment decreases the volume fraction of the phases.In the first stage of solution treatment for 14 h,the tensile properties significantly increase due to the incomplete phase transformation.Although long-term solution treatment sharply decreases the tensile and hardness properties of the alloy,it improves the corrosion resistance due to the transformation of I-phase into W-phase.In fact,it decreases corrosion potential and simultaneously dissolves intermetallic compounds into the a-Mg matrix,resulting in the reduction in galvanic microcells between the matrix and compounds.It is found that the optimum time for long-term solution treatment is 14 h,which improves both corrosion behavior and mechanical properties.     

Zn含量对铸态Mg-2Er合金的微观结构及力学性能影响

采用XRD和SEM等微观表征技术研究不同Zn添加量对Mg-2Er合金微观组织和力学性能的影响。结果表明：当Zn添加量为1%和2%时,合金主要相组成为W相和α-Mg;当Zn添加量为4%-10%时,合金中则有I相析出,合金相成分变为W相、I相和α-Mg;当Zn添加量增加至12%时,W相消失,合金中主要第二相则为I相和Mg4Zn7相。当Zn添加量为6%时,合金具有较好的拉伸力学性能,其抗拉强度、屈服强度和伸长率分别为224 MPa、134 MPa和10.4%。     

Effects of yttrium on microstructure and mechanical properties of Mg-Zn-Cu-Zr alloys

The effects of yttrium addition on microstructure and mechanical properties of as-cast Mg-6Zn-3Cu-0.6Zr-xY(x=0,0.5, 1.0,1.5 and 2.0,mass fraction,%)(ZCK630+xY for short in this study)alloys were investigated by means of OM,XRD and SEM. The results show that the average grain size of Mg-Zn-Cu-Zr magnesium alloy is effectively reduced(from 57μm to 39μm)by Y addition.The analysis of XRD indicates the existence of I-phase(Mg3Zn6Y)and W-phase(Mg3Zn3Y2)in ZCK630 alloys with Y addition.The ultimate tensile strength of ZCK630 alloys is significantly deteriorated with increasing Y addition,which is possibly related to the continuous networks of intergranular phases and the increase of W-phase.     

铸态Mg-6Zn-2Er合金的室温拉伸失效机制

在室温条件下进行了铸态Mg-6Zn-2Er合金的室温拉伸试验。结果表明,该合金的断裂伸长率为5．6％。粗大的第二相,特别是粗大的Mg3Zn3Er2相（W相）是合金失效断裂的主要原因。这表明W相不能有效地实现应力的传递,导致自身内部有裂纹产生。比较可知,合金的基体与第二相间的界面比较稳定,没有裂纹产生。因此,合金第二相的尺寸、分布、形貌和类型显著地影响合金的塑性变形行为。     

高性能Al-Si-Cu-Ni-Mg活塞合金的相分析

采用高倍视频金相显徽镜（HRVM）和电子探针（EPMA）微区分析技术,观察了高性能Al-Si-Cu-Ni-Mg活塞合金的显微组织形貌,确认了合金中存在的构成相Mg2Si、Al3Ni、W相以及（CuNi）2Al3相。着重观察分析W相和Mg2SiN在热处理过程中的形态演变,发现多元共晶体中的W相固溶后由无序网格状呈现出典型的骨架状或者密堆状,Mg2Si相固溶处理后主要以固溶强化相融入到基体中。     

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.     

MICROSTRUCTURE OF Mg-Zn-Zr-Y ALLOYS

In the as-cast Mg-Zn-Zr-Y alloys.the quasierystal phases show massive and eutectoidplate morphologies.The selected area diffraction(SAD)revealed that a large part of the quasicrystals are face-centered icosahedral(FCI),while a small amout of the quasierystals belong to the simple icosahedral(SI)phase.It was found that in homogenized alloys,a part of the grain boundry phases was dissolved,and small massive W-phase and lath-shape MgZn_2 phase dispersedly precipitate in the grains.The transformation of the quasicrystals relates to the temperature.After homogenizing at 360℃,the quasicrystals still present,while after homogenizing at 400℃,the quasicrystals transformed into a new C-typeorthorhombic phase with a=0.975nm,b=1.137nm and c=0.935nm.     

Microstructures and Mechanical Properties of Mg-2Y-xZn (x=1, 2, 3 at%) Alloys

研究了Mg-2Y-xZn(x=1,2,3 at%)合金在铸态、退火态和挤压态的显微组织与力学性能。结果表明:随着合金中Zn含量的增加,合金显微组织中第二相依次为18R-LPSO相、(LPSO+W)混合物和W相。在退火过程中,层片状的14H-LPSO结构析出并沿块状18R-LPSO结构向基体中生长,W相由铸态时弯曲的条纹状转变为颗粒状。经过挤压变形后,LPSO结构和W相均沿挤压方向排列,合金性能得到大幅度提高,其中Mg-2Y-1Zn合金具有最好的室温力学性能,抗拉强度为320 MPa,延伸率达到11.2%。     

Microstructure and Tensile Behavior of Al8Co17Cr17Cu8Fe17Ni33 (at.%) High-Entropy Alloy

Microstructure evolution and tensile behavior of the high-entropy alloy Al₈Co₁₇Cr₁₇Cu₈Fe₁₇Ni₃₃ (at.%) are investigated at room temperature and at 500°C in the as-cast state and under different heat-treatment conditions. Detailed microstructural characterizations are carried out using optical microscopy, scanning electron microscopy, and transmission electron microscopy. The equilibrium phase evolution as a function of temperature was calculated using the Thermo-Calc software (Thermo-Calc Software, Stockholm, Sweden) integrated with TTNi-7 database. The observed majority phase is a face-centered cubic solid solution for all tested specimens. Tensile ductility at room temperature and at elevated temperature is enhanced by heat treatment at 1150°C. An embrittlement phenomenon has been observed after a heat treatment at 700°C resulting in significant degradation in tensile properties.     

Microstructure and corrosion behavior of rapidly solidified Mg-Zn-Y alloys

The effect of a minor change in alloy composition on the microstructure and corrosion properties of melt spun Mg_98.3?xZn_xY_1.7 ribbons with x=9–12 is studied by X-ray diffractometry, differential scanning calorimetry, transmission electron microscopy and a dynamic polarization test. The ribbon specimens with x=9–10 revealed an in-situ composite microstructure consisting of icosahedral quasicrystalline phase (I-phase) particles distributed in an α-Mg matrix. The ribbon specimens with x=11 and 12 contained a minor MgZn₂ phase together with an α-Mg phase and I-phase. With increasing Zn content, the corrosion potential increased because of a mixed potential effect, but the formation of a MgZn₂ phase deteriorated the corrosion property through preferential attack, causing an irregular boundary between the corrosion product and the substrate. These results indicate that it is important to control alloy chemistry not to form the MgZn₂ phase in developing an I-phase strengthened Mg-Zn-Y alloy for structural applications.     

热处理对挤压铸造Mg93YZn6合金组织和性能的影响

采用挤压铸造法制备了Mg93YZn6合金,并对其进行高温热处理,分析了铸态和热处理态的Mg93YZn6合金的微观组织、显微硬度和力学性能。结果表明,该合金的挤压铸造和热处理后的组织中均只有α-Mg基体相和准晶I相生成。经500℃×4h热处理后,合金中的准晶相含量与铸态合金中变化不大。经550℃×2h热处理后,合金中的准晶相有所减少。与铸态合金相比,热处理后合金的硬度、抗拉强度和伸长率均提高。     

双辊激冷铸造A8006合金的均匀化(英文)

通过SEM、XRD与硬度测定研究均匀化过程对双辊激冷铸造(TRC)与直接冷却铸造(DC)A8006合金的微观组织和性能的影响。结果表明,随着TRC合金微观组织的细化,均匀化后合金中的共晶相进一步细化。DC合金均匀化后其共晶相形态相似于TRC合金中的共晶相形态。均匀化后,合金共晶相中的Fe、Mn元素均匀地扩散到铝基体中,引起合金硬度的降低。TRC合金的成形性能优于均匀化的DC合金,所以,对于TRCA8006合金的后续加工过程可省去均匀化过程。     

Microstructural control and hardening response of Mg–6Zn–0.5Er–0.5Ca alloy

The effects of heat treatment on microstructures and hardening response of Mg–6Zn–0.5Er–0.5Ca(wt%) alloy were investigated by optical microscope(OM), scanning electron microscope(SEM), and transmission electron microscope(TEM) in this paper. The results show that the Mg–6Zn–0.5Er–0.5Ca alloy contains Mg_3Zn_6Er_1 quasicrystalline phase(Iphase) and Ca_2Mg_6Zn_3 phase under as-cast condition. Most of the Ca_2Mg_6Zn_3 phases and I-phases dissolve into matrix during heat treatment at 475 ℃ for 5 h. After the as-solution alloy was aged at 175 ℃ for 36 h, a large amount of MgZn_2 precipitate with several nanometers precipitate. It is suggested that the trace addition of Ca results in refining the size of the precipitate, and the presence of the nanoscale MgZn_2 phase is the main factor to improve the peak-aged hardness greatly to 87 HV, which increases about 40 % compared with that of as-cast alloy.     

Microstructure and mechanical properties of AZ31 magnesium alloy reinforced by I-phase

The particles of Mg-Zn-Gd icosahedral quasicrystal master alloy were added into the AZ31 alloy by the repeated plastic working(RPW)process in order to improve the mechanical properties of the AZ31 alloy at room temperature.The microstructure and tensile properties of composites were investigated by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),and tensile testing machine at room temperature.The results suggest that the RPW process can effectively refine the matrix and make the I-phase particles distribute uniformly.The ultimate tensile strength and the yield strength of the composites reach their maximum values of 362.3 and 330.5 MPa,respectively,when the amount of I-phase particles added is10 %.Meanwhile,the elongation of the composites decreases sharply.     

Al含量对CuCrFeMnTiAl高熵合金组织及摩擦磨损行为的影响

根据高熵合金的设计理念制备CuCrFeMnTiAlx(x=0,0.5,1.0,1.5)合金,研究Al含量对该合金系组织结构、硬度及摩擦磨损行为的影响。结果表明:该铸态高熵合金具有简单结构,随Al含量增加,结构由密排六方转变为面心立方;合金的组织为典型的枝晶组织,枝晶间Cu富集的现象明显;合金硬度随着Al含量的增加而升高,其中Al-1.5合金的硬度最高,可以达到7.19GPa;Al-0.5合金在摩擦过程中表面产生氧化区,降低了摩擦系数,因此Al-0.5合金的耐磨性最佳。     

Morphological evolutions of cast and melt-spun Mg_(97)Zn_1Y_2 alloys during deformation and heat-treating

Mg_(97)Zn_1Y_2 alloy has been studied as an elevated temperature creep resistant Mg-based alloy for nearly ten years.While, the strength of the cast Mg_(97)Zn_1Y_2 alloy with long-period stacking(LPS) structure is lower than that of the commercial AZ91 alloy at room temperature.The microstructure evolutions in Mg_(97)Zn_1Y_2(molar fraction,%) alloys with LPS phase,processed by rolling and annealing the as-cast alloy and rapidly solidifying/melt-spinning and age treating at different temperatures respecti...