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.     

Microstructure,Tensile Properties and Work Hardening Behavior of an Extruded Mg–Zn–Ca–Mn Magnesium Alloy

A new Mg-2.2 wt% Zn alloy containing 1.8 wt% Ca and 0.5 wt% Mn has been developed and subjected to extrusion under different extrusion parameters.The finest(～0.48 μm) recrystallized grain structures,containing both nano-sized MgZn_2 precipitates and α-Mn nanoparticles,were obtained in the alloy extruded at 270℃/0.01 mm s~(-1).In this alloy,the deformed coarse-grain region possessed a much stronger texture intensity(～32.49 mud) relative to the recrystallized fine-grain region(～13.99 mud).A positive work hardening rate in the third stage of work hardening curve was also evident in the alloy extruded at 270℃,which was related to the sharp basal texture and which provided insufficient active slip systems.The high work hardening rate in the fourth stage contributed to the high ductility extruded at 270℃/1 mm s~(-1).This alloy exhibited a weak texture,and the examination of fracture surface revealed highly dimpled surfaces.The optimum tensile strength was achieved in the alloy extruded at 270℃/0.01 mm s~(-1),and the yield strength,ultimate tensile strength and elongation to failure were～364.1 MPa,～394.5 MPa and～7.2%,respectively.Fine grain strengthening from the recrystallized fine-grain region played the greatest role in the strength increment of this alloy compared with Orowan strengthening and dislocation strengthening in the deformed coarse-grain regions.     

Effects of Passes on Microstructure Evolution and Mechanical Properties of Mg–Gd–Y–Zn–Zr Alloy During Multidirectional Forging

The multidirectional forging(MDF) process was conducted at temperature of 753 K to optimize the mechanical properties of as-homogenized Mg–13 Gd–4 Y–2 Zn–0.6 Zr alloy containing long-period stacking ordered phase. The effects of MDF passes on microstructure evolution and mechanical properties were also investigated. The results show that both the volume fraction of dynamic recrystallization(DRX) grains and mechanical properties of the deformed alloy enhanced with MDF passes increasing till seven passes. The average grain size decreased from 76 to 2.24 lm after seven passes, while the average grain size increased to 7.12 lm after nine passes. The microstructure after seven passes demonstrated randomly oriented fine DRX grains and larger basal(0001)\11"20[ Schmid factor of 0.31. The superior mechanical properties at room temperature(RT) with ultimate tensile strength(UTS) of 416 MPa and fracture elongation of 4.12% can be obtained after seven passes. The mechanical properties at RT after nine passes are inferior to those after seven passes due to the coarsening of DRX grains, which can be ascribed to the static recovery resulting from the repeated heating at the interval of MDF passes. The elevated temperature mechanical properties of the deformed alloy after seven passes and nine passes were investigated. When test temperature was below 523 K, the elevated temperature tensile yield strength and UTS after seven passes are superior to those after nine passes, while they are inferior to that after nine passes as temperature exceeds523 K.     

Microstructure and Mechanical Properties of Mg–3Al–Zn Magnesium Alloy Sheet by Hot Shear Spinning

Hot shear spinning experiments with Mg–3.0 Al–1.0 Zn–0.5 Mn(AZ31 B, wt%) magnesium alloy sheets were conducted at various temperatures, spindle speeds and feed ratios to investigate the effects of these processing parameters on the microstructure, crystallographic texture and mechanical properties. The AZ31 B sheet displayed good shear formability at temperatures from 473 to 673 K, spindle speeds from 300 to 600 rev/min and feed ratios from 0.1 to 0.5 mm/rev. During the dynamic recrystallization process, the grain size and texture were affected by the deformation temperature of the hot shear spinning process. Each of the spun sheets presented a strong basal texture, and the c-axis of most of the grains was parallel to the normal direction. The optimal hot shear spinning parameters were determined to be a temperature of 473 K, a spindle speed of 300 rev/min and a feed ratio of 0.1 mm/rev. The yield strength, ultimate tensile strength and elongation in the rolled direction reached 221 MPa, 288 MPa and 14.1%, and those in the transverse direction reached 205 MPa, 280 MPa and 12.4%, respectively. The improved strength and decreased mechanical anisotropy resulted from the fine grain size and strong basal texture.     

Microstructure and Tensile Properties of a Nb–Mo Microalloyed 6.5Mn Alloy Processed by Intercritical Annealing and Quenching and Partitioning

The transformation behavior, microstructural evolution and mechanical properties were compared in a coldrolled Nb–Mo microalloyed 6.5Mn alloy after intercritical annealing(IA) and quenching and partitioning(Q P),respectively. The thermodynamic calculation and theoretical analysis were used to determine the optimal heat treatment parameters. The Q P samples exhibited relatively higher strength with relatively low ductility, mainly due to the hard martensite matrix, which resulted in continuous yielding behavior upon loading, whereas the IA samples showed the significantly improved ductility, which benefited from the more sufficient transformation-induced plasticity(TRIP) effects and the softer ultrafine ferrite matrix. The dependence of yield point elongation(YPE) of IA samples on grain size demonstrated that the YPE value was in the reverse proportional relationship to the average grain size, which agreed well with theoretical analysis.     

Effects of ECAP Extrusion on the Microstructure,Mechanical Properties and Biodegradability of Mg–2Zn–xGd–0.5Zr Alloys

Effects of equal channel angular pressing(ECAP) extrusion on the microstructure, mechanical properties and biodegradability of Mg–2Zn– xGd–0.5Zr( x=0,0.5,1,2 wt%) alloys were studied in this work. Microstructure analysis, tensile test at ambient temperature, immersion test and electrochemical test in Hank's solution were carried out. The results showed that Gd could further enhance the grain refinement during the ECAP extrusion. Both Gd addition and ECAP extrusion could improve the mechanical properties of the alloys, and the extrusion played the dominant role. Minor addition of Gd(0.5–1 wt%) could obviously enhance the corrosion resistance of the alloys. To some extent, ECAP extrusion improved the corrosion resistance of the alloys due to the change of second phases distribution and the refinement of grains. Further increase in extrusion pass was detrimental to the improvement of the corrosion resistance as a result of increment of the grain boundaries.     

Effect of Hydrostatic Pressure on LPSO Kinking and Microstructure Evolution of Mg–11Gd–4Y–2Zn–0.5Zr Alloy

Two different kinds of hot compressions, namely normal-compression and can-compression, were performed on the Mg–11 Gd–4 Y–2 Zn–0.5 Zr alloy, featured with long period stacking ordered(LPSO) phase. The kinking behavior of LPSO phase and microstructure evolution was investigated to clarify the effect of levels of imposed hydrostatic pressure. The results suggest that the LPSO phases including both the intragranular 14 H-LPSO phase and intergranular 18 R-LPSO phase suffer severe kinking behavior under higher hydrostatic pressure induced by can-compression, which is firstly characterized with more kinking times and smaller relative kinking width. The main reason for such enhanced LPSO kinking during cancompression may be mainly ascribed to the higher dislocation density under a higher level of hydrostatic pressure. Meanwhile, a competitive relationship between the kink behaviors of intergranular 18 R-LPSO phase and intragranular 14 H-LPSO phase was observed. That is, the intergranular 18 R-LPSO phase only kinks obviously on the condition that the surrounded intragranular 14 H-LPSO phase scarcely kinks. In contrast to the distinctive kinking of LPSO phase, the dynamic recrystallization(DRX) mechanism shows less dependence on the hydrostatic pressure. Resultantly, similar DRX fractions and crystallographic texture were attained for two compression processes owing to the similar operation of deformation mode.     

Enhanced Strength and Corrosion Resistance of Mg–2Zn–0.6Zr Alloy with Extrusion

The microstructure, mechanical properties and corrosion behavior of Mg–2 Zn–0.6 Zr alloy under the as-cast and asextruded conditions were investigated. Microstructure analysis indicated the remarkable grain refinement by extrusion, as well as notable reductions in volume fraction and size of precipitate phases. As compared with the as-cast alloy, the asextruded alloy exhibited better mechanical performance, especially in yield strength which was promoted from 51 to 194 MPa. Refined grains, dispersive precipitate phases and texture were thought to be the main factors affecting the improved performance in strength. The electrochemical measurement and immersion test revealed the corrosion rate of Mg–2 Zn–0.6 Zr alloy by extrusion decreased from 1.68 to 0.32 mm/year. The reasons for the enhanced corrosion resistance were mainly attributed to the decreased volume fraction and Volta potential of the precipitate phases, the refinement of the grain size, as well as the formation of more protective corrosion film.     

Microstructure and Texture Evolution During the Direct Extrusion and Bending–Shear Deformation of AZ31 Magnesium Alloy

AZ31 alloys were extruded by direct extrusion and bending–shear deformation(DEBS). The microstructure characteristic and texture evolution of DEBSed AZ31 sheets were investigated by electron backscattered diffraction(EBSD). It is found that DEBS technique could effectively refine grains and weaken texture. Besides, we also investigate how twinning affects dynamic recrystallization during hot extrusion. {10–12} extension twins can offer nucleation sites and enough energy to trigger dynamic recrystallization. Moreover, the character of direct extrusion and bending–shear die can lead to the activation of non-basal slip system and further dramatically weaken the basal texture of the microstructure with many preactivated basal slip systems.     

Effect of Solution Treatment on Microstructure and Corrosion Properties of Mg–4Gd–1Y–1Zn–0.5Ca–1Zr Alloy

The as-cast multi-element Mg–4Gd–1Y–1Zn–0.5Ca–1Zr alloy with low rare earth additions was prepared, and the solution treatment was applied at different temperatures. The microstructural evolution of the alloy was characterized by optical microscopy and scanning electron microscopy, and corrosion properties of the alloy in 3.5% NaCl solution were evaluated by immersion and electrochemical tests. The results indicate that the as-cast alloy is composed of the a-Mg matrix,lamellar long-period stacking-ordered(LPSO) structure and eutectic phase. The LPSO structure exists with more volume fraction in the alloy solution-treated at 440 °C, but disappears with the increase in the solution temperature. For all the solution-treated alloys, the precipitated phases are detected. The corrosion rates of the alloys decrease first and then increase slightly with the increase in the solution temperature, and the corrosion resistance of the solution-treated alloys is more than four times as good as that of the as-cast alloy. In addition, the alloy solution-treated at 480 °C for 6 h shows the best corrosion property.     

Microstructure,Mechanical Properties and Texture Evolution of Mg-Al-Zn-La-Gd-Y Magnesium Alloy by Hot Extrusion and Multi-Pass Rolling

A high-ductility Mg-8.10Al-0.42Zn-0.51Mn-1.52La-1.10Gd-0.86Y (wt%) alloy was developed by hot extrusion and multi-rolling processes. Relationships between microstructure, mechanical properties and texture evolution of the extruded and rolled alloy were investigated. The rolling process had significant effect on grain refinement of the extruded plate. The grain size reduced from 12.3 to 4.9 μm with the increasing rolling pass. With the increase in rolling pass, the proportion of dynamic recrystallized (DRXed) grains increases due to particle-stimulated nucleation, grain boundary nucleation and twin induced nucleation. In the process of multiple rolling, the basal pole gradually tilted from normal direction to transverse direction due to the asymmetric deformation and irregular grain deformation, resulting in the weakening of the base texture. The results showed that grain refinement and texture weakening were the main reasons for the good ductility of the alloy.     

Microstructural Evolution and Anisotropic Weakening Mechanism of ZK60 Magnesium Alloy Processed by Isothermal Repetitive Upsetting Extrusion

The isothermal repetitive upsetting extrusion (RUE) was implemented to process ZK60 magnesium alloy at 380 °C. Then, the relationship between the microstructural characters, including grain refinement and texture evolution, and the mechanical performance of the alloy was investigated. Results showed that after 3 passes of RUE, the average grain size was refined from 115.0 to 26.5 μm, which was mainly caused by the continuous dynamic recrystallization and discontinuous dynamic recrystallization. Meanwhile, the elongation of the alloy increased from 13.8 to 21.6%, and the superplasticity (142%) of the alloy has been achieved in the following high temperature tensile test, which is very beneficial for the further processing of the alloy into components. In particular, the alloy formed a distinctive texture distributed between < 2-1-11 > and < 2-1-14 > , which was greatly related to the Schmid factor of extrusion direction (ED) and transverse direction (TD). This texture changed the initiation ability of basal and prismatic slip in both directions and inhibited the initiation of partial tensile twinning in TD; thus, the anisotropy in both directions was weakened. As expected, the tensile yield strength difference decreased from 25.9 to 3.4 MPa, but it was used as the cost of tensile yield strength in ED.     

Effect of Extrusion Strain Path on Microstructure and Properties of AZ31 Magnesium Alloy Sheet

The mechanical properties of AZ31 magnesium alloy sheets processed by different extrusion strain paths were examined in correlation with concurrent microstructure and texture evolution. The conventional extrusion(CE) and asymmetric extrusion(ASE) paths were performed on Mg alloy sheets. The textures at near surface and mid-layer of ASE sheets were various throughout sheet thickness direction as a result of extra asymmetric shear strain. This can stimulate the orientation of(0002) basal planes to incline approximately 12° toward the shear direction. Moreover, the basal texture of ASE sheet was weakened compared with CE one. Enhancing the ambient formability of extruded Mg alloy sheet fabricated by ASE path was accomplished by the tilted weak basal texture.     

Improvement of Mechanical Properties of Magnesium Alloy ZK60 by Asymmetric Reduction Rolling

The improvement of mechanical properties of ZK60 processed by asymmetric reduction rolling(ARR) was investigated in this paper. The grain refinement and basal texture intensity decrease were attributed to the introduction of shear stress produced by ARR process. Compared to conventional symmetrical rolled(SR) ZK60 alloys, ARRed ZK60 exhibited finer, more homogeneous grains and higher mechanical properties. The intensity of basal texture of ARRed ZK60 after annealing was lower than that of SRed ZK60 after annealing. ZK60 sheet with good combination of strength and ductility could be obtained by ARR process. The yield strength(YS) and ultimate tensile strength(UTS) of the ARRed ZK60 sheet were increased 150% and 91.3%, compared to those of SRed ZK60 sheet, from 80 to 200 MPa and from 140 to264 MPa, respectively. Simultaneously, the elongation to failure increased by 68.75% in the ARR sheet(27%) when compared to that of the SR sheet(16%).     

超细晶Mg-2.5Zn-1Ca合金制备及其组织性能研究

通过挤压+等通道转角挤压(ECAP)复合加工工艺制备了超细晶Mg-2.5Zn-1Ca合金,采用OM、SEM、XRD、EBSD等手段分析变形过程中微观结构演变特征,结合力学性能变化,研究变形过程中合金强化机制。结果表明,经挤压+ECAP变形后,晶粒与第二相颗粒明显细化,其中挤压+2道次ECAP后获得了均匀的细晶组织,平均晶粒尺寸约1.1μm;同时,细小的Ca₂Mg₆Zn₃颗粒弥散分布于基体中。晶粒细化是剧烈塑性变形、动态再结晶和细小弥散的Ca₂Mg₆Zn₃相共同作用的结果。ECAP变形使合金的力学性能显著提高,2道次有最高的抗拉强度和延伸率,分别为275 MPa和17%。随着ECAP变形道次的增加,织构强度逐渐减弱,基面织构逐渐转变为一种新的织构,并且ECAP变形合金有较高的非基面施密特因子,组织均匀细化,使得材料有更好的延伸率。     

挤压比对热挤压AZ80镁合金管材组织和性能的影响

选用不同的挤压比对变形镁合金AZ80进行管材热挤压工艺试验研究,对挤压前后材料组织与力学性能的变化进行分析。结果表明,热挤压可以显著细化AZ80镁合金的晶粒,而且随着挤压比的增加,晶粒变得更加细小;增大挤压比也可以提高AZ80镁合金的抗拉强度和屈服强度。结果表明,挤压比为18.2,坯料温度为390℃,模具预热温度为360℃,凹模的半模角为60°～70°,可得到均匀的合金组织和良好的力学性能。     

热挤压工艺对ZK60合金组织及性能的影响

对均匀化及挤压 时效(T5)后的ZK60合金的组织和拉伸性能进行了研究.结果表明,铸态ZK60合金经450℃×14h均匀化处理后,得到几乎单相固溶体,伸长率较铸态提高80.5%,塑性大大提高.合金经挤压 时效后,晶粒明显细化,其力学性能均得到不同程度的提高.尤其是在挤压温度为300℃,挤压比为30、45的工艺条件下可获得较优的综合性能.     

ZK60＋Y镁合金塑性变形后组织和性能研究

对真空熔炼后的ZK60 Y镁合金在380℃下进行热挤压,随后取部分挤压棒在400℃下轧制成厚3mm的薄板。通过金相分析、室温力学拉伸试验、透射电镜分析研究了经塑性变形的ZK60 Y镁合金显微组织及力学性能。结果表明,薄板的显微组织中有大量的第二相,大部分呈条带状分布在基体上,透射电镜分析表明这些第二相颗粒包括纳米级大小的颗粒;经过轧制的薄板的抗拉强度、屈服强度和伸长率均较挤压后的棒材有所下降,薄板的抗拉强度、屈服强度和伸长率分别为263MPa、235MPa和15%。