Evolutions of Microstructure and Mechanical Properties in Mg-5Li-1Zn-0.5Ag-0.5Zr-xGd Alloy

The evolution of the microstructure and mechanical properties of alloy system with nominally composition Mg-5Li-1Zn-0.5Ag-0.5Zr-xGd (x = 0, 1.2, 2.4, 3.6, 4.8, 6) is evaluated based on computational phase diagram and corresponding experimental studies. The results show that grains are significantly refined with the increase of Gd content. The main phases of as-cast alloys are α-Mg, β-Li, AgLi₂Mg, and Mg₃Gd. With the increase of Gd content, the amounts of Mg₃Gd phase and β-Li phase have been increased. When the Gd content exceeds 3.6 wt%, Mg₃Gd phase precipitates in a form of the network at the grain boundaries. The precipitation of β-Li can be attributed to the competitive dissolution of Zn, Gd, and Li in Mg. Meanwhile, γ″ is formed after the addition of Gd, which grows and transforms into γ′ with the increase of Gd content. In solidification process, stacking faults are formed by solid transformation of partial α-Mg and Mg₃Gd. Eventually, with the synergistic effect of Mg₃Gd, β-Li, and γ″ (or γ′), as the Gd content increasing, the tensile strength of the alloy first increases, then decreases, and the elongation decreases. When the content of Gd is 4.8 wt%, the ultimate tensile strength and yield strength reach the maximum values of 227 MPa and 139 MPa, and the elongation is 18.1%, respectively.     

Influence of yttrium on microstructure and mechanical properties of as-cast Mg-5Li-3Al-2Zn alloy

The influence of Y on microstructure and mechanical properties of as-cast Mg-5Li-3Al-2Zn alloy was investigated. The results show that the phase compositions of Mg-5Li-3Al-2Zn consist of α-Mg and AlLi phases. Adding Y to the alloy results in the formation of Al₂Y compound and facilitates grain refinement. The addition of 0.8 wt.% Y produces the smallest grain size. The tensile tests performed at room temperature show that the additions of Y can improve the mechanical properties of the alloy; the tensile strength and ductility reach peak values when the Y additions are 0.8 wt.% and 1.2 wt.%, respectively. The mechanisms of improvement are related to grain refinement and compound strengthening effects.     

Mg-8Li-4Al-0.3Y合金微观组织与力学性能研究

利用光学显微镜(OM)、扫描电子显微镜(SEM)和X射线衍射仪(XRD)等手段系统研究了铸态、固溶处理态和挤压态Mg-8Li-4Al-0.3Y合金的微观组织,测试了其室温力学性能。实验结果表明：铸态实验合金主要由ɑ-Mg、β-Li、Al2Y和AlLi相以及MgAlLi2相组成;固溶处理后合金中在相界处分布的MgAlLi2化合物相消失,大量AlLi相发生分解并固溶于合金基体中,仅剩下部分尺寸较大的AlLi相。在挤压过程中合金发生动态再结晶,显微组织明显细化,组织更加均匀。固溶处理后合金基体硬度明显高于铸态合金;与铸态相比,挤压态合金的综合力学性能得到大幅提升,其抗拉强度和延伸率分别达到208 MPa和25.1%。     

Microstructure and mechanical properties of Mg-5.6Li-3.37Al-1.68Zn- 1.14Ce alloy

Mg-5.6Li-3.37Al-1.68Zn-1.14Ce alloy was prepared using vacuum induction melting furnace. The microstructure and phases compostion of as-cast and as-extruded alloys were investigated by optical microscopy, energy dispersive X-ray spectroscopy, scanning electron mocroscopy and X-ray diffraction. The mechanical properties of these alloys were measured with tensile tester. The results indicate that the as-cast alloy is composed of a（Mg） phase and rod-like Al2Ce compound. Al2Ce has the refining effect on the microstructure of alloy. During the extrusion at 523 K, dynamic recrystallization happens in the alloy. The dynamic recrystallization refines the grain size of alloy obviously. The phases are refined clearly after extrusion deformation, and the strength and ductility of the alloy are increased accordingly.     

挤压温度对Mg-6Zn-1Mn-4Sn-0.5Y镁合金组织和性能的影响

通过光学显微镜（OM）,X 射线衍射（XRD）,扫描电子显微镜（SEM）,电子背散射衍射（EBSD）以及拉伸试验对360和420℃挤压的Mg-6Zn-1Mn-4Sn-0.5Y变形镁合金的组织和性能进行了研究。研究结果表明,合金铸态和时效态的相组成为α-Mg, Mn, Mg7Zn3, Mg2Sn, 和 MgSnY相。挤压温度从360℃增加到420℃,动态再结晶完成,晶粒长大,合金的屈服强度,抗拉强度以及延伸率分别由259MPa, 350MPa 和 18.3% 降低至 239MPa, 332MPa和12.5%。理论计算和拉伸试验结果表明,细晶强化和固溶强化对合金屈服强度的增加产生决定性影响。     

Mg-2Zn-0.5Y镁合金半固态等温处理过程中的微观组织演变

本文研究了挤压Mg-2Zn-0.5Y合金在半固态等温处理过程中的微观组织演变规律。结果表明：挤压态的Mg-2Zn-0.5Y合金包含α-Mg,I相和W相三种物相,并且平均晶粒尺寸为7μm。在温度为793K的半固态等温热处理过程中,晶粒不断长大,直到保温时间达到4min时才出现液相。随着等温处理温度和时间的增加,α-Mg固相颗粒不断长大,并且逐步被液相分离;同时,出现在晶界的液相与颗粒内部的液滴都在不断地增多。研究还发现,当固相率较高的时候,晶粒间的合并机制与固相颗粒再熔化机制同时起主导作用;然而当固相率较低的时候,Ostwald熟化机制是主要的粗化机制,同时也可以观察到晶粒间的合并。     

Microstructure characterization and mechanical properties of Mg-9Li-5Al-1Zn-0.6RE alloy

Mg-9Li-5Al-1Zn-0.6RE alloy was prepared by vacuum induction heating. The microstructure and phases composition of the alloy were analyzed with optical microscope, scanning electron microscope and X-ray diffractometer. Then the effect of homogenization temperature on microstructure and mechanical properties of the alloy was studied. The hardness of samples under different homogenization temperatures was measured. The results show that, the alloy is composed of a phase, β phase, Mg17Al12 and AlLi. RE added into the alloy is solved in a phase and β phase completely. After homogenization heat treatment, the needle-like a phase disappears. With the increase of homogenization temperature, the shape of a phase is spherical-like first, then vennicular-like, and large block-like finally. The variation of the shape of a phase causes the hardness of sample to change accordingly. The most favorable homogenization temperature for microstructure and mechanical properties is 150 ℃.     

复合添加Si、Nd元素对Mg-11Li-3Al合金组织与力学性能的影响

利用磁悬浮真空高频感应加热法熔炼高质量的镁锂合金,通过Si、Nd元素复合添加来研究其对Mg-11Li-3Al合金组织与力学性能的影响。结果表明:加入Si、Nd元素后,组织中主要生成Mg_2Si和Al_(11_Nd_3 2种第二相,其中Si的添加能够促使合金组织中形成篆体形貌的黑色析出物聚集区,而Nd的加入能够细化这种黑色棒状的析出物,并减小晶粒尺寸、洁净组织。当Nd的添加量为1%(质量分数)时其晶粒细化的效果最佳。经过XRD和EDS分析发现,这种黑色棒状的析出物为Mg_2Si相和Al_(11)Nd_3相的结合体。铸态合金的抗拉强度随着Si含量的增加递增,最后趋于稳定;其塑性并不会随某一种或是复合元素的添加而单调变化。实验得到了一种综合力学性能最佳的合金Mg-11Li-3Al-1Si-1Nd,其抗拉强度和伸长率分别为212.3 MPa和46.2%。     

铸态Mg-2Zn-1.5Cu合金组织及力学性能

利用金相显微镜、扫描电镜、透射电镜、XRD物相分析以及力学性能测试等手段,研究了Mg-2Zn-1.5Cu(at%)合金的显微组织及力学性能。结果表明:铸态合金存在较为明显的元素偏析,主要的第二相为MgCuZn相;合金的力学性能随着温度的提高而不断降低,塑性变化幅度要明显高于强度,合金的断裂方式也由低温时的沿晶断裂转变为高温时的穿晶断裂;在相同温度下,随着应力的提升,合金的稳态蠕变速率提高,蠕变机制由晶界控制转变为晶界及位错共同控制;在相同的应力下,随着温度的提升,合金的稳态蠕变速率存在数量级的提升,蠕变激活能由130kJ/mol降低到36.4 kJ/mol;在200℃,45 MPa时,出现加速蠕变阶段,发生蠕变断裂,断口存在明显的穿晶断裂特征,基体中有大量的沿基面运动的位错,部分位错发生攀移,MgZnCu相具有减缓蠕变变形的作用。     

Mg-5Al-1Sr-2Ca-xY合金组织及力学性能

制备了不同Y含量的Mg-5Al-1Sr-2Ca-xY(x=0,1,2,5)合金试样,采用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)、材料试验机等观察测试合金的微观组织和力学性能。结果表明,未添加Y时,合金晶粒大小不均匀,且多呈柱状,晶内有较多的点状化合物;Y含量1%时,晶粒细化、球化且大小较均匀;Y含量2%时,晶粒趋于柱状;Y含量5%时,晶粒形状不规则、大小极不均匀。随Y含量的增加,室温和高温力学性能呈先升后降趋势,最高点为Y含量1%,其室温和高温抗拉强度分别较无Y合金提高了约33.8%和25.4%。     

Effect of Ce on microstructure, mechanical properties and corrosion behavior of high-pressure die-cast Mg-4Al-based alloy

Mg-4Al-xCe-0.3Mn (x = 0, 1, 2, 4 and 6 wt.%) alloys were prepared by high-pressure die-casting. The microstructures, mechanical properties and corrosion behavior were investigated. The cross-section of test bar is divided into the fine skin region and the relatively coarse interior region by a narrow band. The dendritic arm spacing is greatly reduced and the secondary phases Al₁₁Ce₃ and (Al, Mg)₂Ce with the former being the dominant one substitute the Mg₁₇Al₁₂ phase with addition of Ce. When Ce content reaches 4 wt.%, the alloy exhibits an optimal cost performance ratio. The improved mechanical properties maintained up to 200 °C are mainly related to the fine grain size and the main strengthening phase Al₁₁Ce₃, which is present in a high volume fraction, and possesses fine acicular morphology and relatively good thermal stability. The improved corrosion resistance is attributed to the microstructure modification of the alloys and the corrosion product films.     

Microstructures and mechanical properties of cold rolled Mg-8Li and Mg-8Li-2Al-2RE alloys

The microstructures and mechanical properties of Mg-8Li and Mg-8Li-2Al-2RE alloy sheets were evaluated after cold rolling.Both alloys contain α-phase and β-phase which consists of a solid solution of Mg in BCC Li.The proportion ofβ-phase in both alloys is approximately 60%.Theα-phase andβ-phase are elongated approximately parallel to the rolling direction and there is no sign of recrystallization even after being annealed at 200℃for 1 h.The yield strength of Mg-8Li-2Al-2RE sheets is about 165 MPa with elongation of 35%along rolling direction,while the yield strength is about 187 MPa with elongation of 21%along the direction titled 45ü to rolling direction.Theα-phase in both alloys exhibits basal texture,and the intensity of basal texture in Mg-8Li is larger than that in Mg-8Li-2Al-2RE.However,theβ-phase shows(100)texture,and the intensity of(100)texture in Mg-8Li is twice of that in Mg-8Li-2Al-2RE.It could be attributed to the existence of RE-containing particles in Mg-8Li-2Al-2RE.     

钆对Mg-8Li-4Zn-xGd合金铸态组织与力学性能的影响

采用锂盐熔剂保护熔铸Mg-8Li-4Zn-xGd(x=1,3,5)合金铸锭,研究钆含量对铸态合金组织和力学性能的影响。结果表明:Mg-8Li-4Zn-xGd合金基体由α-Mg(HCP)和β-Li(BCC)双相构成。随着钆含量的增加,Mg₅Gd共晶相和Zn₁₂Gd化合物相逐渐连成网状,将基体α+β双相隔离成20～40μm的等轴状或类似于铸铁中的共晶团状,可有效细化α-Mg相和连续的β-Li相;组织中大颗粒Mg₂Zn₁₁相弥散分布在β-Li相内,Mg₅₁Zn₂₀相分布在α-Mg晶界处;锌元素还可以在β-Li相中析出细小弥散分布的MgZn相,其数量随钆含量的增加而增加,可直接弥散强化β-Li相。此外,锌和钆对合金硬度的影响较大,随着钆含量的增加,合金的抗拉强度提高,但伸长率降低。     

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.     

Y参杂对真空热压烧结TiAl基合金显微组织和力学性能的影响

Ti-45Al (at %)和Ti-45Al-0.3Y (at %)样品通过真空热压烧结的方法制备。样品通过x射线衍射(XRD)、光学显微镜(OM)、背散射电子(BSE)以及压缩和硬度测试来研究Y参杂和热压工艺参数对TIAl基合金的显微组织和力学性能的影响。最优烧结参数为压力42MPa,在1400℃下保温保压90分钟。在此参数下,得到了组织均匀、晶粒细小的由γ相和γ+α2片层结构组成的双态组织。在热压温度1400℃,保温时间240分钟下,反应能完全达到,但会出现晶粒粗大现象。Y的加入对细化晶粒和片层间距有明显的作用,这有助于提高合金的机械强度。     

高合金化Al-9Zn-2Mg-2Cu-0.3Ce合金均匀化过程中的组织演变

采用光学显微镜(OM)、扫描电镜(SEM)、电子探针显微分析(EPMA)、X射线衍射(XRD)以及差示扫描量热仪(DSC),研究了一种高合金化Al-9Zn-2.0Mg-2Cu-0.3Ce(质量分数,%)合金的铸态微观组织,以及其均匀化过程中微观组织的演变,获得了较优的单级均匀化工艺。结果表明:铸态时,合金晶粒内部枝晶网络发达,Zn、Mg、Cu元素偏聚严重,合金中主要的非平衡凝固相为T(AlZnMgCu) 相和θ(Al₂Cu)相。经过470 ℃×48 h均匀化热处理后,合金中的枝晶网络基本消除,凝固相T逐渐回溶至基体中,主要的残留相为耐高温相Al₂CuMg、Al₈Cu₄Ce和Al₇Cu₂Fe。扩散动力学分析表明,470 ℃退火48 h的单级均匀化工艺足以使合金中的非平衡相回溶至基体中。     

ZM81-xSn (x = 0, 2, 4, 6, 8 and 10)变形镁合金的组织演变和力学性能

通过对不同Sn含量的ZM81合金的微观组织和力学性能的测得,研究了Sn在ZM81合金中的存在形式和作用机制及不同添加量对合金显微组织和力学性能的影响。研究结果表明：Sn元素主要以Mg2Sn共晶相形式存在,能够细化铸态组织;热挤压过程中,Sn添加能够起到抑制动态再结晶和晶粒细化的作用;T6处理,尤其是双级时效,能显著提升挤压态合金的力学性能,其中ZM81-4Sn合金具有最佳的综合力学性能,抗拉强度、屈服强度和延伸率分别为416MPa、393MPa和4.1%。实验合金高强度主要源于MgZn2和Mg2Sn析出相的双重时效强化效果;相比单级时效,双级时效态合金的析出相细小弥散,因此其力学性能更优。     

Microstructural evolution and mechanical performance of cast Mg-3Nd-0.2Zn-0.5Zr alloy with Y additions

This work investigated the effects of different Y additions (0, 1.5, 3.0 and 4.5 wt.%) on the microstructural evolution and mechanical performance of cast Mg-3Nd-0.2Zn-0.5Zr alloy. The results show that as the Y content increases, the key secondary phases in as-cast alloys change from the Mg₁₂Nd type to the Mg₂₄Y₅ type. Meanwhile, the number density of Zn-Zr particles in the grains of as-quenched alloys gradually decreases. HAADF-STEM observations of peak-aged samples reveal that element Y is greatly enriched in the globular β′ precipitates, leading to a significantly increased volume fraction and promoted precipitation kinetics of β′ precipitates, resulting in enhanced strength of the alloy. Tensile tests reveal that, with the addition of 4.5 wt.% Y, the yield strength of the base alloy is substantially increased by 88 and 61 MPa after being aged at 200 and 225 °C under peak-aged conditions, respectively.     

M-Y-Zr-Nd 合金微观结构、力学性能、电磁屏蔽性能的研究

制备了不同Nd含量的Mg-Y-Zr-xNd合金铸锭,研究了Nd含量对微观结构、力学性能和电磁屏蔽性能的影响。实验结果表明,当Nd含量增加到2.63%时,晶粒尺寸从70.1μm细化到42.9μm,并且在晶界不连续分布骨骼状β相。随着Nd含量增加,合金强度和电磁屏蔽性能都会增加。Nd含量为2.63%时同时具有良好的强度和电磁屏蔽性能,T6处理能进一步提高屏蔽效能。根据分析以上实验结果是由于Nd的添加量不同引起微观结构不同造成的。     

Mg-5.5Al-0.5Y-xSm合金的显微组织和力学性能

采用XRD、OM、SEM和EDS等手段研究了Mg-5.5Al-0.5Y-xSm(x=0~2.0%)合金的显微组织和力学性能。实验结果表明,加入适量的Sm后,合金晶粒和Al2Y相得到细化,Mg17Al12相数量减少,同时基体中出现高熔点相Al2Sm相。随着Sm含量的增加,合金的室温(25℃)和高温(150℃和175℃)力学性能先升高后降低,且在Sm含量为1%时达到最佳。