AZ91D镁合金屑的固相再生(英文)

利用固相再生技术回收利用AZ91D镁合金屑,具体工艺为先冷压再热挤。结果表明:制备的AZ91D镁合金具有较好的力学性能且晶粒明显细化。在热挤出过程中发生了动态再结晶,且动态再结晶组织受到热挤温度和应变速率的影响,在300-350 °C下基面滑移和孪晶协调变形导致动态再结晶晶粒产生,形成"项链"组织;在 350-400 °C下位错的交滑移控制动态再结晶形核;高于400 °C时位错攀移控制了整个动态再结晶过程,形成均匀的再结晶组织。随着应变速率增加AZ91D镁合金力学性能增大,改善了材料的力学性能,但应变速率过大,制备试样表面出现裂纹,影响材料的力学性能。     

固相再生AZ91D镁合金边角料的低温力学性能

采用固相再生方法回收AZ91D镁合金边角料,研究再生合金的低温力学性能、微观组织和断口形貌。在WDW-3100型微机控制电子万能试验机上进行低温拉伸实验,实验温度为27,-70,-100和-130℃;在JB30A型冲击试验机上进行冲击实验,温度分别为27,（-70±5）和（-130±5）℃。结果表明：再生合金在固相再生过程中发生了动态再结晶,块与块之间结合较好,原始的块与块之间的界面已经不能分辨。再生合金随着温度的降低,抗拉强度略有增加,伸长率呈下降趋势,即温度降低脆性倾向增加,在-130℃时拉伸,抗拉强度和伸长率分别为360.65MPa和5.46%;随着冲击温度的降低,再生合金的冲击功随之降低,在-130℃时冲击功为3.06J/cm2。     

Deformation Mechanism and Hot Workability of Extruded Magnesium Alloy AZ31

Using the flow stress curves obtained by Gleeble thermo-mechanical testing, the processing map of extruded magnesium alloy AZ31 was established to analyze the hot workability. Stress exponent and activation energy were calculated to characterize the deformation mechanism. Then, the effects of hot deformation parameters on deformation mechanism,microstructure evolution and hot workability of AZ31 alloy were discussed. With increasing deformation temperature, the operation of non-basal slip systems and full development of dynamic recrystallization(DRX) contribute to effective improvement in hot workability of AZ31 alloy. The influences of strain rate and strain are complex. When temperature exceeds 350 °C, the deformation mechanism is slightly dependent of the strain rate or strain. The dominant mechanism is dislocation cross-slip, which favors DRX nucleation and grain growth and thus leads to good plasticity. At low temperature(below 350 °C), the deformation mechanism is sensitive to strain and strain rate. Both the dominant deformation mechanism and inadequate development of DRX deteriorate the ductility of AZ31 alloy. The flow instability mainly occurs in the vicinity of 250 °C and 1 s-1.     

AZ91镁合金的挤压和析出硬化行为(英文)

挤压比为4:1,将铸态AZ91镁合金分别在250,300和350℃下进行挤压,随后进行析出硬化处理(T6)。经过热挤压和析出硬化处理后,铸态AZ91镁合金中粗大的和偏析Mg17Al12析出相被细化并均匀分布在α-镁基体中。在不同的挤压温度下合金中发生了部分或全部动态再结晶。经挤压后,该合金的极限抗拉强度从铸态的190MPa增加到570MPa。AZ91镁合金的时效硬化特征与晶粒尺寸有关。在250、300和350℃下以4:1的挤压比挤压该合金后,获得峰值硬度的时效时间分别为35、30和20h。SEM观察到在AZ91基体中存在均匀细小的Mg17Al12析出相。     

AZ31和AZ91镁合金等温挤压及挤压后的微观组织变化

通过等温挤压和金相观察,研究了AZ31和AZ91镁合金不同变形条件下的挤压性能和变形后的微观组织变化。结果表明,AZ31镁合金的挤压变形性能较好,而AZ91镁合金在挤压比为4∶1、挤压温度为400℃,以及在挤压比为9∶1、挤压温度为350℃和400℃时,挤压后的试件表面均出现了裂纹;AZ31镁合金的最佳成形温度为300℃～400℃,AZ91镁合金的最佳成形温度为300℃～350℃;镁合金在热挤压过程中发生了动态再结晶,挤压之后合金的晶粒显著细化。     

AZ31镁合金热压缩过程中晶粒取向和织构的演变

利用电子背散射衍射(EBSD)取向成像技术分析AZ31铸态镁合金在不同温度和真应变下热压缩的晶粒取向和织构特点,从晶粒取向和织构角度分析不同温度下其动态再结晶(DRX)的类型。结果表明:在热压缩过程中,350℃时,AZ31铸态镁合金表现为连续动态再结晶(CDRX)特征,新晶粒取向与基体相似,具有较强的{0002}基面织构,以基面滑移为主;500℃时,为旋转动态再结晶(RDRX)特征,真应变为0.5时,新晶粒取向与基体偏转成一定角度,具有两种主要的基面织构,由于动态再结晶的定向形核、择优核心长大和旋转动态再结晶造成这两种基面织构弱于350℃时的{0002}基面织构;且随着真应变的增加,其中一种织构由于滑移系的改变而逐渐消失。     

Effect of extrusion ratio on microstructure and mechanical properties of AZ91D magnesium alloy recycled from scraps by hot extrusion

A method for recycling AZ91D magnesium alloy scraps directly by hot extrusion was studied. Various microstructural analyses were performed using the techniques of optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy(EDS). Microstructural observations revealed that all the recycled specimens consisted of fine grains due to the dynamic recrystallization. The main strengthening mechanism of the recycled specimen was grain refinement strengthening and homogeneous distribution of oxide precipitates. The interfaces of individual scraps of extruded materials were not identified when the scraps were extruded with the extrusion ratio of 40:1. Oxidation layers of the scraps were broken into pieces by high compressive and shear forces under the extrusion ratio of 40:1. The ultimate tensile strength and elongation to failure increased with increasing the extrusion ratio. Recycled specimens with the extrusion ratio of 40:1 showed higher ultimate tensile strength of 342.61 MPa and higher elongation to failure of 11.32%, compared with those of the cast specimen.     

Hot deformation behavior and microstructure evolution of a Mg–Gd–Nd–Y–Zn alloy

The hot deformation behavior of homogenized Mg–6.5Gd–1.3Nd–0.7Y–0.3Zn alloy was investigated during compression at temperatures of 250–400 ℃ and at strain rates ranging from 0.001 to 0.100 s~(-1). Microstructure analyses show that the flow behaviors are associated with the deformation mechanisms. At the lower temperatures(250–300 ℃), deformation twinning is triggered due to the difficult activation of dislocation cross-slip. Dynamic recrystallization(DRX) accompanied by dynamic precipitation occurs at the temperature of 350 ℃ and influences the softening behavior of the flow.DRX that develops extensively at original grain boundaries is the main softening mechanism at the high temperature of 400 ℃ and eventually brings a more homogeneous microstructure than that in other deformation conditions. The volume fraction of the DRXed grains increases with temperature increasing and decreases with strain rate increasing.     

Integrated Extrusion-Shear Forming Process of the Solid-State Recycled AZ80 Magnesium Alloy via Hot Press Sintering

The consolidation recycled AZ80 billets were successfully fabricated through the cold press and hot press sintering of the AZ80 metal chips.The consolidation recycled billets sintered at 350℃present the comparable compressive properties and inferior tensile properties compared with the initial cast billets.The defects in the consolidation recycled billet were inclined to propagate along the bond interface between the metal chips during tension,which resulted in the inferior tensile properties of the recycled billets.The recycled billets were then subjected to the integrated extrusion-shear(ES) process.The homogeneous finer dynamic recrystallization grains with an average grain size of 6 μm can be obtained in the shear deformation zone and extrusion sizing zone through integrated ES process at 300℃with an extrusion velocity of 0.6 mm/s.The recycled billets after integrated ES forming process present rival tensile properties compared with the initial cast billets after integrated ES forming with the same extrusion parameters,which can be ascribed to that the integrated ES forming can nearly eliminate the defects through the severe compressive and shear strain.The solid-state recycling process through hot press sintering and subsequent integrated ES process can fabricate the consolidation recycled AZ80 rod,which demonstrates the comparable tensile properties with the cast-extrusion rod.     

Dynamic recrystallization kinetics of as-cast AZ91D alloy

The flow behavior and dynamic recrystallization (DRX) behavior of an as-cast AZ91D alloy were investigated systematically by applying the isothermal compression tests in temperature range of 220–380 °C and strain rate range of 0.001–1 s^?1. The effect of temperature and strain rate on the DRX behavior was discussed. The results indicate that the nucleation and growth of dynamic recrystallized grains easily occur at higher temperatures and lower strain rates. To evaluate the evolution of dynamic recrystallization, the DRX kinetics model was proposed based on the experimental data of true stress-true strain curves. It was revealed that the volume fraction of dynamic recrystallized grains increased with increasing strain in terms of S-curves. A good agreement between the proposed DRX kinetics model and microstructure observation results validates the accuracy of DRX kinetics model for AZ91D alloy.     

Comparative study of the deformation behavior of hexagonal magnesium–lithium alloys and a conventional magnesium AZ31 alloy

Specimens of a conventional magnesium AZ31 alloy and a binary α-solid solution Mg4Li alloy with similar starting textures and microstructure were subjected to plane strain deformation under various deformation temperatures ranging from 298 K to 673 K. Lithium addition to magnesium exhibited remarkable room temperature ductility improvement owing to enhanced activity of non-basal slip, particularly, 〈c + a〉-slip mode. Furthermore, the addition of lithium to magnesium seemed to reduce the plastic anisotropy, typical for commercial magnesium alloys. This was evident in the flow curves and texture development obtained at 200 °C and 400 °C. At 400 °C prismatic slip gains strong influence in accommodating the imposed deformation. In terms of thermal stability against microstructure coarsening at elevated temperatures, the lithium containing alloy undergoes significant grain growth following recrystallization.     

Mechanical properties and microstructures of a wrought AZ91 alloy

Effects of hot plastic deformation on microstructures and tensile properties of AZ91 alloy were investigated. Compared with as-T4 microstructures, the as-extruded samples of AZ91 alloy with fine grains exhibit better strength and ductility due to dynamic recrystallization. The succeeded rotation forging also provides freer grains while the strength increases, but the elongation decreases. Simultaneously, wrought AZ91 alloy shows more balance properties than as-T4 condition ones. An interesting elongation of 228.5% is attained in the as-extruded AZ91 alloy in spite of the coarse grains with the size of 85 μm. The two-step method enhances the superplastic property of AZ91 alloy. The microstructure is still keeping the same scale of grains after superplastic testing.     

Simulation of strain-softening behaviors in an AZ31 Mg alloy showing distinct twin-induced reorientation before a peak stress

To investigate strain-softening behavior during plastic deformation of an AZ31 Mg alloy, cylindrical specimens were compressed in a rolling direction at 300 °C. Experimental evidence revealed that an inhomogeneous microstructure evolved due to the softening behavior associated with deformation at elevated temperatures. The large grains that reoriented as a result of deformation twinning were free of dynamic recrystallization (DRX). Fine grains nucleated at grain boundaries of grains were deformed by a slip-dominated mechanism, which accommodated the external strain. A visco-plastic self-consistent (VPSC) polycrystal model was used to simulate softening of the flow stress curve and texture evolution during uniaxial compression. A softening scheme was implemented in the polycrystal model to predict the softening phenomenon and texture evolution after the peak stress. The original VPSC model was modified to simulate texture evolution in an AZ31 Mg alloy that exhibited twin-dominated deformation before the peak stress.     

TiC/AZ91D composites fabricated by in situ reactive infiltration process and its tensile deformation

1 Introduction Relative to aluminum matrix composites, magnesium-matrix composites are receiving interests increasingly in recent years due to their low densities and high specific properties. They are potentially attractive for the applications in aeros…     

Thermal expansion and dimensional stability of unidirectional and orthogonal fabric M40/AZ91D composites

Unidirectional (60%, volume fraction) and orthogonal (50%, volume fraction) M40 graphite fibre reinforced AZ91D magnesium alloy matrix composites were fabricated by pressure infiltration method. The coefficients of thermal expansion (in the temperature range of 20-350 ℃) and dimensional stability (in the temperature range of 20-150 ℃) of the composites and the corresponding AZ91D magnesium alloy matrix were measured. The results show that coefficients of thermal expansion of the composites in longitudinal direction decrease with elevating temperature. The coefficients of thermal expansion (CTE) for unidirectional M40/AZ91D composites and orthogonal M40/AZ91D composites are 1.24×10-6 ℃-1 and 5.71×10-6 ℃-1 at 20 ℃, and 0.85×10-6 ℃-1 and 2.75×10-6 ℃-1 at 350 ℃, respectively, much lower than those of the AZ91D alloy matrix. Thermal cycling testing demonstrates that the thermal stress plays an important role on residual deformation. Thus, a better dimensional stability is obtained for the AZ91D magnesium alloy matrix composites. More extreme strain hysteresis and residual plastic deformation are observed in orthogonally fabric M40 reinforced AZ91D composite, but its net residual strain after each cycle is similar to that of the unidirectional M40/AZ91D composite.     

热拉伸变形对AZ31B镁合金薄板显微组织的影响

利用单向热拉伸实验和金相显微镜研究了AZ31B镁合金薄板热变形过程及其动态再结晶组织变化规律。结果表明,在变形温度为160℃、应变速率为1×10-3s-1时,拉伸变形后得到的显微组织是混合组织。260℃~280℃时形成均匀分布的细小等轴晶粒,其晶粒平均尺寸为5μm左右。在变形温度为320℃~400℃、变形速率为1×10-3s-1~3.3×10-4s-1时,晶粒平均尺寸为10μm~20μm,沿晶界出现氧化现象,且氧化"黑色"斑点发生聚集。     

Effect of hot extrusion on microstructures and mechanical properties of SiC nanoparticles reinforced magnesium matrix composite

Particulate reinforced magnesium matrix nanocomposite prepared with semisolid stirring assisted ultrasonic vibration was subjected to extrusion at 350 °C with an extrusion ratio of 12:1. Extrusion of the SiCp/AZ91 nanocomposite induced large scale dynamic recrystallization resulting in a fine matrix microstructure. There were two kinds of zones in the extruded nanocomposite: SiC nanoparticle bands parallel to the extrusion direction and refined-grain zones between the SiC nanoparticle bands. In the SiC nanoparticle bands, there were SiC nanoparticles along the boundaries of refined grains. The distribution of SiC nanoparticles was uniform although some agglomerates of SiC nanoparticles still existed in the SiC nanoparticle bands. The ultimate tensile strength, yield strength and elongation to fracture of the SiCp/AZ91 nanocomposite were simultaneously improved by extrusion. Results from the extruded SiCp/AZ91 nanocomposite tensile testing at different temperatures (75, 125, 175 and 225 °C) revealed an increase of the tensile strength and ductility values compared with the unreinforced and extruded AZ91 alloy.     

低温慢速挤压和电脉冲处理制备具有优异力学性能的AZ91双峰合金

通过低温慢速挤压(LTSRE)和电脉冲处理(EPT)获得具有双峰结构的AZ91 镁合金,这种结构由粗大的尺寸为20～60 μm 的未再结晶晶粒和细小的尺寸约为200 nm 的再结晶晶粒组成.双峰晶粒结构的形成原因主要是LTSRE过程中的不均匀变形以及EPT对于变形AZ91 镁合金静态再结晶的加速效应.与常规热处理时的静...     

Influence of strain rate on microstructure and formability of AZ31B magnesium alloy sheets

The effects of strain rate on microstructure and formability of AZ31B magnesium alloy sheets were investigated through uniaxial tensile tests and hemispherical punch tests with strain rates of 10^?4, 10^?3, 10^?2, 10^?1 s^?1 at 200 °C. The results show that the volume fraction of dynamic recrystallization grains increases and the original grains are gradually replaced by recrystallization grains with the strain rate decreasing. A larger elongation and a smaller r-value are obtained at a lower strain rate, moreover the erichsen values become larger with the strain rate reducing, so the formability improves. This problem arises in part from the enhanced softening and the coordination of recrystallization grains during deformation.     

AZ31B镁合金塑性变形动态再结晶的实验研究

通过不同应变速率和不同温度下的轴对称压缩试验,研究了AZ31B镁合金塑性变形与动态再结晶的相互依赖关系。研究证实,温度T在200℃～400℃区间、变形程度ε约0.2左右时,开始出现动态再结晶(DRX)现象。随变形程度的增加,DRX晶粒不断增多,材料呈现明显的软化趋势,流动应力下降。当DRX过程完成以后,继续变形,材料又出现硬化行为。为镁合金塑性变形组织演变的定量研究打下了基础。