Effects of ultrasonic treatment on microstructure and mechanical properties of Mg-6Zn-0.5Y-2Sn alloy

The effects of the ultrasonic treatment on the microstructure and mechanical properties of Mg-6Zn-0.5Y-2Sn alloy were investigated. The results show that the ultrasonic treatment has significant effect on the microstructure and mechanical properties of Mg-6Zn-0.5Y-2Sn alloy. The phases in Mg-6Zn-0.5Y-2Sn alloy are α-Mg, MgZn2, MgSnY, Mg2Sn, and a small amount of I-phase. With the application of ultrasonic treatment, I-phase nearly disappears, and with increasing the ultrasonic treatment power, the coarse dendrites gradually change into roundish equiaxed grains. The second phases at the α-Mg boundaries transform from coarse, semicontinuous and non-uniform to fine, discontinuous, uniform and dispersive. When the ultrasonic treatment power is 700 W, the best comprehensive mechanical properties of Mg-6Zn-0.5Y-2Sn alloy are obtained. Compared with the untreated alloy, the 0.2%tensile yield strength, ultimate tensile strength and elongation are improved by 28%, 30%and 67%, respectively.

Constitutive modeling for dynamic recrystallization kinetics of Mg-4Zn-2Al-2Sn alloy

In order to have a better understanding of the hot deformation behavior of the as-solution-treated Mg-4 Zn-2 Sn-2 Al（ZAT422） alloy, a series of compression experiments with a height reduction of 60% were performed in the temperature range of 498-648 K and the strain rate range of 0.01-5 s～（-1） on a Gleeble 3800 thermo-mechanical simulator. Based on the regression analysis by Arrhenius type equation and Avrami type equation of flow behavior, the activation energy of deformation of ZAT422 alloy was determined as 155.652 k J/mol, and the constitutive equations for flow behavior and the dynamic recrystallization（DRX） kinetic model of ZAT422 alloy were established. Microstructure observation shows that when the temperature is as low as 498 K, the DRX is not completed as the true strain reaches 0.9163. However, with the temperature increasing to 648 K, the lower strain rate is more likely to result in some grains＇ abnormal growth.

Microstructure evolution and optimum parameters analysis for hot working of new type Mg-8Sn-2Zn-0.5Cu alloy

The hot deformation behavior of as-solutionized Mg 8Sn 2Zn 0.5Cu(TZC820)alloy was investigated experimentally and numerically via isothermal compression tests at 250400℃and strain rate range of 0.013 s 1 on a Gleeble 1500D thermomechanical simulator.Results show that the deformation temperature and strain rate signi cantly affected ow stress and material constants.In addition,the strain-compensated constitutive relationship was established on the basis of true stress strain curves.The main deformation mechanism for this alloy was the dynamic recrystallization(DRX),and the DRX degree was effectively enhanced with an increase in deformation temperature and a decrease in strain rate.Moreover,the cellular automaton method was used to simulate the microstructure evolution during hot compression.In addition,the processing maps were established,and the optimum deformation parameters for the as-solutionized TZC820 alloy are at 370400℃and 0.01 s 1,and at 320360℃and 13 s 1.

Effect of non-isothermal retrogression and re-ageing on through-thickness homogeneity of microstructure and properties of Al-8Zn-2Mg-2Cu alloy thick plate

In order to improve the through-thickness homogeneity and properties of aviation aluminum alloy thick plate.The effect of heating-cooling retrogression and re-ageing on the performance of Al-8Zn-2Mg-2Cu alloy thick plate was investigated by hardness tests, electrical conductivity tests and transmission electron microscopy(TEM) observation.Results revealed that, during retrogression heating, the fine pre-precipitates in surface layer dissolve more and the undissolved η′ or η phases are more coarsened than that of center layer. During slow cooling after retrogression,precipitates continue coarsening but with a lower rate and the secondary precipitation occurs in both layers. Finer precipitates resulting from the secondary precipitation are more in surface. However, the coarsening and secondary precipitation behaviors are restrained in both layers under quick cooling condition. The electrical conductivity and through-thickness homogeneity of precipitates increases while the hardness decreases with cooling rate decreasing. After the optimized non-isothermal retrogression and re-ageing(NRRA) including air-cooling retrogression, the throughthickness homogeneity which is evaluated by integrated retrogression effects has been improved to 94%. The tensile strength, fracture toughness and exfoliation corrosion grade of Al-8Zn-2Mg-2Cu alloy plate is 619 MPa, 24.7 MPa·m^(1/2)and EB, respectively, which indicates that the non-isothermal retrogression and re-aging(NRRA) could improve the mechanical properties and corrosion resistance with higher through-thickness homogeneity.

Microstructures and mechanical properties of Mg-2%Zn-0.4%RE alloys

The solidification microstructures and hardness of Mg-2%Zn (mass fraction) based alloys with addition of 0.4%Ce, 0.4%Gd, 0.4%Y or 0.4%Nd (mass fraction) were investigated, and the effects of the rare earth elements on the microstructures and mechanical properties of these alloys extruded at 310℃ were also compared. The results indicate that the trace rare earth Ce, Gd, Y or Nd in the Mg-2%Zn alloy has obviously different grain refinement effects on its solidification microstructures, and the as-cast and hot-extruded alloy with 0.4%Ce has the smallest average grain size and the highest strength. However, the extruded alloys containing 0.4%Nd or 0.4%Y with the elongation of 26.6% and 30%, respectively, show higher plasticity in spite of lower strength as compared with the alloy containing 0.4%Ce.

Grain refinement impact on the mechanical properties and wear behavior of Mg-9Gd-3Y-2Zn-0.5Zr alloy after decreasing temperature reciprocating upsetting-extrusion

Based on the deforming technique of severe plastic deformation(SPD), the grain refinement of a Mg-9Gd-3Y-2Zn-0.5Zr alloy treated with decreasing temperature reciprocating upsetting-extrusion(RUE) and its influence on the mechanical properties and wear behavior of the alloy were studied. The RUE process was carried out for 4 passes in total, starting at 0 ℃ and decreasing by 10 ℃ for each pass. The results showed that as the number of RUE passes increased, the grain refinement effect was obvious, and the second phase in the alloy was evenly distributed. Room temperature tensile properties of the alloy and the deepening of the RUE degree showed a positive correlation trend, which was due to the grain refinement, uniform distribution of the second phase and texture weakening. And the microhardness of the alloy showed that the microhardness of RUE is the largest in 2 passes. The change in microhardness was the result of dynamic competition between the softening effect of DRX and the work hardening effect. In addition, the wear resistance of the alloy showed a positive correlation with the degree of RUE under low load conditions. When the applied load was higher, the wear resistance of the alloy treated with RUE decreased compared to the initial state alloy. This phenomenon was mainly due to the presence of oxidative wear on the surface of the alloy, which could balance the positive contribution of severe plastic deformation to wear resistance to a certain extent.

In vitro and in vivo evaluation of effects of Mg-6Zn alloy on tight junction of intestinal epithelial cell

The effects of biodegradable Mg?6Zn alloy on tight junction of intestinal epithelial cells (IEC-6) were investigated. In the in vitro experiments, the cells were exposed to Mg?6Zn alloy extracts with different concentrations (0, 20% and 40%) for 1, 3 and 5 d. The real-time polymerase chain reaction (PCR) results show that when the cells are treated with 40% and 20% extracts, the expression of Zona Occludens 1 (ZO-1) and Occludin increase as compared with those in the control group. In the in vivo experiments, Mg?6Zn alloy and titanium staples were implanted into rabbits’ intestinal tract for 1, 2 and 3 weeks. By immunohistochemical staining of peri-implant intestinal tissue, increased expression of Occludin and ZO-1 are observed in the Mg?6Zn alloy groups as compared with those in the titanium and control groups. The results show that Mg?6Zn alloy in intestine may promote the regeneration of tight junction, and the extract with a certain concentration can induce the expression of tight junction related genes in IEC-6 cells.

Effect of heat treatment on microstructures and mechanical properties of sand-cast Mg-4Y-2Nd-1Gd-0.4Zr magnesium alloy

Influence of heat treatment on the microstructures and mechanical properties of sand-cast Mg-4Y-2Nd-1Gd-0.4Zr magnesium alloy was investigated,and the tensile fracture mechanisms of the studied alloys under different conditions were also discussed.The results show that the optimum T4 and T6 heat treatment conditions for the as-cast Mg-4Y-2Nd-1Gd-0.4Zr alloy are 525°C,8 h and（525°C,8 h）＋（225°C,16 h）,respectively,with regard to the microstructure observation,DSC heating curve and mechanical properties.The hardness,yield strength,ultimate tensile strength and elongation of the Mg-4Y-2Nd-1Gd-0.4Zr alloy treated by optimum T6 heat treatment are HV91,180 MPa,297 MPa and 7.4%,respectively.Moreover,the Mg-4Y-2Nd-1Gd-0.4Zr alloys under different heat treatment conditions exhibit different tensile fracture modes.

Microstructure of 18R-type long period ordered structure phase in Mg_(97)Y_2Zn_1 alloy

The microstructure of the 18R-type long period stacking ordered （LPSO） phase in Mg 97 Y 2 Zn 1 alloy was investigated by the first principles calculation. The arrangement rule of Zn and Y atoms in the LPSO structure is determined theoretically. The calculation results reveal that the additive atoms are firstly located in the fault layers at the two ends of the 18R-type LPSO structure, and then extend to fault layers in the interior, which is in good agreement with the experimental observations. This feature also implies the microstructural relationship between 18R and other LPSO structures. The cohesive energy and the formation heat indicate the dependence of the stability of 18R LPSO structure on contents of Y and Zn atoms. The calculated electronic structures reveal the underlying mechanism of microstructure and the stability of 18R LPSO structure.

熔体处理对Mg-6Gd-3Y-0.4Zr-2Zn镁合金组织的影响

通过重力铸造法制备了Mg-6Gd-3Y-0.4Zr-2Zn合金熔体,采用机械振动、机械搅拌、超声波不同方式对合金熔体进行了处理。研究了熔体处理对Mg-6Gd-3Y-0.4Zr-2Zn合金微观组织的影响。结果表明:不同方式处理的合金熔体,合金晶粒都得到了细化,第二相分布弥散。超声波处理后铸造缺陷消失。

Microstructure and mechanical properties of Mg_(94)Zn_2Y_4 extruded alloy with long-period stacking ordered structure

The microstructure and mechanical properties of Mg94Zn2Y4 extruded alloy containing long-period stacking ordered structures were systematically investigated by SEM and TEM analyses. The results show that the 18R-LPSO structure and α-Mg phase are observed in cast Mg94Zn2Y4 alloy. After extrusion, the LPSO structures are delaminated and Mg-slices with width of 50-200 nm are generated. By ageing at 498 K for 36 h, the ageing peak is attained andβ′phase is precipitated. Due to this novel precipitation, the microhardness ofα-Mg matrix increases apparently from HV108.9 to HV129.7. While the microhardness for LPSO structure is stabilized at about HV145. TEM observations and SAED patterns indicate that the β′ phase has unique orientation relationships betweenα-Mg and LPSO structures, the direction in the close-packed planes ofβ′precipitates perpendicular to that ofα-Mg and LPSO structures. The ultimate tensile strength for the peak-aged alloy achieves 410.7 MPa and the significant strength originates from the coexistence ofβ′precipitates and 18R-LPSO structures.

Microstructure of Mg-8Zn-4Al-1Ca aged alloy

The microstructure of Mg-8Zn-4Al-1Ca aged alloy was investigated by TEM and HRTEM. The results show that the hardening produced in the Mg-8Zn-4Al-1Ca alloy is considerably higher than that in the Mg-8Zn-4A1 alloy. A dense dispersion of disc-like Ca2Mg6Zn3 precipitates are formed in Mg-8Zn-4Al-1Ca alloy aged at 160 ℃ for 16 h. In addition, the lattice distortions, honeycomb-looking Moir＆#233; fringes, edge dislocations and dislocation loop also exist in the microstructure. The precipitates of alloy aged at 160 ℃ for 48 h are coarse disc-like and fine dispersed grainy. When the alloy is subjected to aging at 160 ℃ for 227 h, the microstructure consists of numerous MgZn2 precipitates and Ca2Mg6Zn3 precipitates. All the analyses show that Ca is a particularly effective trace addition in improving the age-hardening and postponing the formation of MgZn2 precipitates in Mg-8Zn-4Al alloy aged at 160 ℃.

Mg-2.5Nd-1Cd-0.6Zr-0.4Zn镁合金的力学性能和阻尼性能

研究了铸态和固溶态下Mg-2.5Nd-1Cd-0.6Zr-0.4Zn镁合金的力学性能及阻尼行为。结果表明,固溶处理提高了合金抗拉强度、伸长率。室温下,铸态和固溶态合金的应变无关阻尼性能相当。该合金其应变相关阻尼随应变振幅的增大而增大,且固溶态的阻尼明显高于铸态的。合金的阻尼行为可采用Granato-Lucke位错阻尼理论解释。

固溶温度对Mg-2Gd-2Zn轧制板材显微组织和力学性能的影响

采用OM、SEM、EDS、XRD、显微硬度计和力学试验机研究了400℃、430℃、460℃、490℃和520℃不同固溶温度对轧制态Mg-2Gd-2Zn合金板材组织结构和力学性能的影响。结果表明,当温度不高于490℃时,晶粒尺寸随固溶温度升高几乎呈线性增长趋势。第二相颗粒也随固溶温度升高总体呈减少趋势。但在490℃固溶温度下,第二相反而增加,且呈细小弥散分布。此时显微硬度达最大值,为77.88HV,固溶时效强化效果显著。XRD分析结果表明,当固溶温度从430℃升高到490℃时,第二相主要由MgZn_2和GdZn_5的初生相转变为MgZn_2和GdZn的沉淀相。490℃固溶处理下合金板材沿RD、TD和45°方向的抗拉强度均达到最大值,分别为262 MPa、244 MPa和254 MPa;断裂伸长率略有降低,分别为34%、31%和39%,但塑性各向异性降低。

Zr含量对Mg-2Gd-1Zn合金显微组织及力学性能的影响

为了改善Mg-2Gd-1Zn铸造镁合金的凝固组织,提高其力学性能,采用光学显微镜(OM),X射线衍射(XRD)、维氏硬度和拉伸-压缩试验机等手段,评价不同Zr含量对Mg-2Gd-1Zn镁合金表面微观形貌和力学性能的影响。实验结果显示,Zr含量能够显著影响Mg-2Gd-1Zn镁合金凝固组织和力学性能。随着Zr含量的增加,合金的晶粒逐渐细化,而合金的力学性能却随之先增加后减小。因此,为了提高Mg-2Gd-1Zn镁合金的力学性能,应该向Mg-2Gd-1Zn镁合金中添加1%的Zr元素。

Ca对Mg-5Li-3Al-2Zn合金组织和力学性能的影响

实验研究了添加1%、2%、3%、6%Ca对Mg-5Li-3Al-2Zn合金组织和性能的影响。通过观察显微组织,利用XRD和EDS分析组织成分可知,添加适量的Ca可细化晶粒,Ca主要富集在晶界处,当Ca加入量超过2%时,与Al形成Al_2Ca金属间化合物,Al_2Ca较多时,对基体的割裂作用较强。室温拉伸试验结果表明,添加2%Ca,强度和塑性同时提高,继续增加Ca含量,合金的力学性能下降。

TEM microstructure of rapidly solidified Mg-6Zn-1Y-1Ce alloy

Rapidly solidified（RS） Mg-6Zn-1Y-1Ce ribbons were prepared by single roller melt-spinning technique.Transmission electron microscopy and energy dispersive X-ray spectroscopy were employed to characterize the microstructure of RS ribbons.The results show that there is high density of particles distributed within grains and at grain boundaries in the region near wheel side.The particle density is decreased in the middle region and free surface region.The alloy is predominantly composed of supersaturated--Mg solid solution,T phase and W phase;meanwhile,a few icosahedral quasicrystalline and Mg4Zn7 particles are also observed.The T phase is confirmed having a body-centered orthorhombic structure that is transformed from the body-centered tetragonal structure Mg12Ce phase due to the partial substitution of Mg atoms by Zn.

热处理对Mg-5Zn2Al镁合金组织及性能的影响

采用金相显微镜、电子万能试验机、扫描电镜等研究了热处理对Mg-5Zn2Al镁合金组织及性能的影响。结果表明:试验合金在经过320℃固溶36h,175℃时效16h后的合金的晶粒尺寸明显增大,晶界却变得细小,晶界上析出物明显增多,而且合金经过热处理之后,该成分合金的抗拉强度达到最大243MPa,伸长率达11.3%,使铸态下的Mg-5Zn2Al镁合金相比综合力学性能得到了显著的提高。

Influence of I-phase and W-phase on microstructure and mechanical properties of Mg-8Li-3Zn alloy

Microstructures and mechanical properties of LZ83?xY alloys containingI-phase andW-phase were investigated by XRD, OM, SEM and EDS. The experimental results show that the content ofI-phase andW-phase changes by varying Zn/Y mass ratio in the LZ83?xY alloys. The cohesion ofI-phase/α-Mg eutectic pockets can enhance the strength in the as-cast LZ83?0.5Y and LZ83?1.0Y alloys, while theW-phase has no obvious strengthening effect on the LZ83?1.5Y alloy. In the extruded alloys, the I-phase andW-phase were extruded into the particles with nanoscale size in theβ-Li matrix phase. The dispersion strengthening of W-phase was more obvious because of the higher volume fraction. The ultimate tensile strength of extruded LZ83?1.5Y alloy is up to 238 MPa while the elongation is up to 20%.

纳米ZrO_(2)颗粒增强Mg-6Zn合金复合材料组织及性能

采用搅拌铸造法制备了纳米ZrO_(2)增强的Mg-6Zn合金。利用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)和维氏硬度仪对xwt.%ZrO_(2)/Mg-6Zn(x=0,1,3,5)复合材料的微观组织及性能进行了表征分析。结果表明,纳米ZrO_(2)颗粒加入到镁熔体中未观察到明显的反应产物,其稳定存在于Mg基体中;大量的纳米ZrO_(2)颗粒主要分布在晶界处,并且随着ZrO_(2)含量的增加团聚愈加明显。与Mg-6Zn基体合金相比,随着添加纳米ZrO_(2)含量的增加,复合材料的晶粒尺寸呈现先减小后增大的现象,相应的复合材料的硬度值同样也呈现先增大后减小的现象。当纳米ZrO_(2)的添加量为1wt.%,复合材料展现出了较为均匀的组织和良好的力学性能,其硬度值为HV52.09,较基体合金提高了14.2%。