Microstructure and Mechanical Properties in Friction Stir Welded Thick Al–Zn–Mg–Cu Alloy Plate

In this work, 20-mm-thick aluminum-alloy plates were joined via friction stir welding. The temperature gradient was reduced by reducing the surface welding heat input to achieve uniformity of the mechanical properties across the thick plate joints. The welding temperature was measured using thermocouples. The microstructures were observed via electron backscatter diff raction and transmission electron microscopy. The tensile properties of the samples sliced along the thickness direction of the j...     

Enhancing Mechanical Properties of Mg–6Zn Alloy by Deformation-Induced Nanoprecipitation

We presented the solution of deformation-induced precipitation after homogenization to enhance the mechanical properties of Mg–6 Zn alloys. The results show that the improved strategy exhibits more effective strengthening role than grain refinement methods based on low-temperature severe plastic deformation under the same strain. The low-temperature deformation with larger extrusion ratio results in massive nano-sized precipitates and excellent mechanical properties with the yield strength of 355 MPa and the ultimate tensile strength of 405 MPa. The increased mechanical properties are strong and tough enough to resist the stress and not be worn away when the alloy nail penetrates through the pig thigh bone, potentially extending more orthopedic surgery applications for Mg–Zn alloys.     

Microstructure and Mechanical Properties of Mg–7.4% Al Alloy Matrix Composites Reinforced by Nanocrystalline Al–Ca Intermetallic Particles

Mg–7.6% Al(in mass fraction) alloy matrix composites reinforced with different volume fractions of nanocrystalline Al3Ca8 particles were synthesized by powder metallurgy,and the effect of the volume fraction of reinforcement on the mechanical properties was studied.Room temperature compression test reveals considerable improvement on mechanical properties as compared to unreinforced matrix.The compressive strength increases from 683 MPa for unreinforced alloy matrix to about 767 and 823 MPa for the samples having 20 and 40 vol% of reinforcement,respectively,while retaining appreciable plastic deformation ranging between 12 and 24%.The specific strength of the composites increased significantly,demonstrating the effectiveness of the low-density Al3Ca8 reinforcement.     

Effect of Extrusion Temperature on the Microstructure and Mechanical Properties of Mg–5Al–2Ca Alloy

In this work, the Mg–5Al–2Ca alloy was extruded at 573, 623 and 673 K, with a ratio of 16:1 and a constant speed of 3 mm/s. Results demonstrate that the Al2Ca particle is formed in Mg–5Al–2Ca alloy. The size, amount and distribution of Al2Ca particles are influenced evidently by extrusion temperature. Unlike previous reports, the intensity of basal texture increases with increasing extrusion temperature, and the reasons are analyzed and given. Even though the average grain size increases as the extrusion temperature increased from 573 to 623 K, the YS, UTS and elongation of asextruded Mg–5Al–2Ca alloy are almost kept the same at 573 and 623 K. The reason is speculated as the balance of grain size, Al2Ca phase and texture at the two temperatures. The work hardening rate depends on extrusion temperature, and the largest θ value of Mg–5Al–2Ca alloy is obtained when the extrusion was performed at 623 K.     

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.     

Evolution of Microstructure,Residual Stress,and Tensile Properties of Mg–Zn–Y–La–Zr Magnesium Alloy Processed by Extrusion

The microstructure, texture, residual stress, and tensile properties of Mg–6 Zn–2 Y–1 La–0.5 Zr(wt%) magnesium alloy were investigated before and after extrusion process, which performed at 300 °C and 400 °C. The microstructural characterizations indicated that the as-cast alloy was comprised of α-Mg, Mg–Zn, Mg–Zn–La, and Mg–Zn–Y phases. During homogenization at 400 °C for 24 h, most of the secondary phases exhibited partial dissolution. Extrusion process led to a remarkable grain refi nement due to dynamic recrystallization(DRX). The degree of DRX and the DRXed grain size increased with increasing extrusion temperature. The homogenized alloy did not show a preferential crystallographic orientation, whereas the extruded alloys showed strong basal texture. The extrusion process led to a signifi cant improvement on the compressive residual stress and mechanical properties. The alloy extruded at 300 °C exhibited the highest basal texture intensity, the compressive residual stress and hardness, and yield and tensile strengths among the studied alloys.     

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.     

Characterization of Microstructure and Mechanical Properties of Mg–8Li–3Al–1Y Alloy Subjected to Different Rolling Processes

The mechanical properties and microstructure evolution of Mg–8Li–3Al–1Y alloy undergoing different rolling processes were systematically investigated. X-ray diffraction, optical microscope, scanning electron microscopy, transmission electron microscopy as well as electron backscattered diffraction were used for tracking the microstructure evolution. Tensile testing was employed to characterize the mechanical properties. After hot rolling, the MgLi₂Al precipitated in β-Li matrix due to the transformation reaction: β-Li?→?β-Li?+?MgLi₂Al?+?α-Mg. As for the alloy subjected to annealed hot rolling, β-Li phase was clearly recrystallized while recrystallization rarely occurred in α-Mg phase. With regard to the microstructure undergoing cold rolling, plenty of dislocations and dislocation walls were easily observed. In addition, the microstructure of alloys subjected to annealed cold rolling revealed the formation of new fresh α-Mg grains in β-Li phase due to the precipitation reaction. The mechanical properties and fracture modes of Mg–8Li–3Al–1Y alloys can be effectively tuned by different rolling processes.     

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.     

Effect of Precipitate State on Mechanical Properties,Corrosion Behavior,and Microstructures of Al–Zn–Mg–Cu Alloy

The mechanical properties, corrosion behavior and microstructures of the Al–Zn–Mg–Cu alloy under various ageing treatments were investigated comparatively. The results show that the tensile strength and corrosion resistance are strongly affected by the precipitate state. Massive fine intragranular precipitates contribute to high strength. Discontinuous coarse grain boundary precipitates containing high Cu content, as well as the narrow precipitate free zone, result in low corrosion susceptibility. After the non-isothermal ageing (NIA) treatment, the tensile strength of 577 MPa is equivalent to that of 579 MPa for the T6 temper. Meanwhile, the stress corrosion susceptibility r_tf and the maximum corrosion depth are 97.8% and 23.5 μm, which are comparable to those of 92.8% and 26.7 μm for the T73 temper. Moreover, the total ageing time of the NIA treatment is only 7.25 h, which is much less than that of 48.67 h for the retrogression and re-ageing condition.     

热挤压工艺对AZ31镁合金组织与力学性能的影响

在不同挤压条件下对AZ31镁合金进行了热挤压试验,并对挤压前后材料组织与力学性能的变化进行了分析.研究结果表明,AZ31镁合金热挤压时发生了动态再结晶,材料组织比铸态时细化,力学性能大幅度提高;AZ31镁合金挤压后的组织及力学性能受挤压温度及冷却方式影响,在本试验范围内,AZ31镁合金在623 K挤压后空冷得到的组织均匀细小,力学性能良好.     

AZ31镁合金轧制变形后组织性能研究

本文研究了不同轧制变形量和轧制速度对AZ31镁合金板材微观组织和力学性能的影响。轧制变形可显著细化AZ31镁合金板材的晶粒尺寸并提高其综合力学性能。当轧制速度为5m/min,轧制变形量为50%时,板材平均晶粒尺寸最细可达到9μm,其抗拉强度、屈服强度和延伸率分别提高到280MPa、180MPa和30%以上,同时探讨了AZ31镁合金屈服强度与晶粒大小之间的关系。在大量AZ31镁合金轧制相关文献和本文一系列实验研究的基础上,对比分析了不同轧制工艺对AZ31镁合金综合力学性能的影响。研究表明,本文所采用轧制工艺可显著提高AZ31镁合金板材的综合力学性能,同时降低板材轧向和横向的各向异性。     

异步轧制对AZ31镁合金板材组织和性能的影响

对不同轧制温度、道次压下量以及轧制路径等工艺条件下所制备的AZ31镁合金板材的组织和性能进行了研究。结果表明．当温度由623K升到723K时，晶粒发生长大，孪晶消失，板材的抗拉强度由275MPa降到250MPa，伸长率则由14．5％增加到18％；当道次压下量从5％增加到20％时，晶粒逐渐得到细化，板材的抗拉强度由道次压下量为5％时的265MPa增加到20％时的300MPa，伸长率则由18％降到15％；轧制路径的改变，使不同板材中孪晶的数量产生改变，路径A中的孪晶较多，伸长率较低，强度较高，路径D中的孪晶较少，伸长率较高．强度较低。     

异步轧制对AZ31镁合金板材组织和性能的影响

对不同轧制温度、道次压下量以及轧制路径等工艺条件下所制备的AZ31镁合金板材的组织和性能进行了研究。结果表明,当温度由623K升到723K时,晶粒发生长大,孪晶消失,板材的抗拉强度由275MPa降到250MPa,伸长率则由14.5%增加到18%;当道次压下量从5%增加到20%时,晶粒逐渐得到细化,板材的抗拉强度由道次压下量为5%时的265MPa增加到20%时的300MPa,伸长率则由18%降到15%;轧制路径的改变,使不同板材中孪晶的数量产生改变,路径A中的孪晶较多,伸长率较低,强度较高,路径D中的孪晶较少,伸长率较高,强度较低。     

稀土Y对AZ31镁合金金相组织和力学性能酌影响

研究了稀土元素Y对AZ31镁合金金相组织和力学性能的影响。结果表明：当稀土添加量为0．6％～0．9％时，仅（Mg）基体晶粒变细，并且加入量为0．9％时得到更细化的组织，13相（Mg17Al12）在晶界由连续网状变为断续弥散状分布，由于α（Mg）基体晶粒的细化和p柏形貌的改善，合金的力学性能有提高；当稀土添加量为1．2％时，α（Mg）基体晶粒显著粗化，β相（Mg17Al12）内部出现针状和圆盘状的第二相，力学性能下降。     

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.     

Mg-3Al-1Zn-0.8Nd合金等温压缩变形流变应力与组织的研究

在AZ31B镁合金中添加0．8％的稀土元素Nd,应用Gleeble-1500D热／力学模拟试验机,在不同变形温度、不同应变速率下对AZ31B-0．8Nd镁合金的流变应力进行了研究。结果表明,镁合金在等温压缩变形过程中,变形温度和应变速率对流变应力和组织有显著的影响,流变应力随着变形温度的升高和应变速率的降低而降低,变形温度在350～400℃,应变速率为0．1s^-1条件下合金的组织细小均匀。     

稀土元素对AZ31镁合金组织和力学性能的影响

研究了稀土元素钕、铈、镧三种元素对AZ31镁合金组织和力学性能的影响。结果表明：随着稀土含量的增加AZ31镁合金的组织得到细化,相应的力学性能也得到了提高。原因是加入稀土元素以后,镁合金中的β相（Mg17Al12）在晶界由连续网状变为断续弥散状分布,由于α（Mg）基体晶粒的细化和β相形貌的改善,合金的力学性能得以提高。     

高精度AZ31镁合金薄壁管件等温挤压后的组织与性能

研究了不同条件下AZ3l镁合金管材的等温挤压情况,并对挤压前后材料组织与力学性能的变化进行了分析.研究结果表明,AZ31镁合金热挤压时发生了动态再结晶,材料组织比铸态时细化,力学性能大幅度提高;在(653±10)K挤压温度范围内金属流动均匀,挤出管材尺寸精度较高,力学性能良好;从综合性能看,AZ31镁合金挤压产品的合适退火工艺为573 K × 2 h;此时管材的机械拉伸强度为260 MPa,伸长率为23%.     

Ca变质及热挤压对AZ31镁合金组织的影响

研究了金属Ca变质处理及热挤压变形对镁合金组织、晶粒大小的影响.结果表明:0.4%的Ca能使AZ31镁合金的β-Mg_(17)Al_(12)组织明显球化,均匀化处理后晶粒尺寸由变质前的546μm降至147μm;另外,400℃下热挤压也能强烈地细化组织,平均晶粒尺寸降至20μm以下,其机理是发生了动态再结晶与孪生变形.