表面扩渗Al,Zn处理对ZM5镁合金性能的影响

通过铝锌(Al,Zn)混合粉对ZM5镁合金进行了表面固态扩渗铝锌(Al,Zn)处理,在衬底形成了Mg-Al-Zn合金层.研究结果表明:Mg-Al-Zn合金层主要由Mg-Al-Zn固溶体和Mg-Al-Zn金属间化合物(Al6Mg10Zn,Al5MgllZn4)组成,该合金层不仅使ZM5镁合金表面合金层显微硬度显著提高,而且在盐水浸泡腐蚀过程中,在衬底与腐蚀介质之间起到了良好的屏障作用,从而赋予试样良好的腐蚀性能.     

Microstructure evolution of processed Mg-Al-Zn alloy by equal channel angular extrusion in semi-solid isothermal treatment

1Introduction Thixoforming is one of the best methods regarding manufacture of Mg-Al-Zn alloy components because of its low resistance of deformation compared with solid metal forging and high mechanical properties of formed components compared with liqui…     

Processing of AZ31 magnesium alloy by accumulative roll-bonding at gradient temperature

In the present investigation a wrought magnesium alloy AZ31 was successfully processed by the accumulative roll-bonding (ARB) at gradient temperature up to six cycles with the lowest temperature of 250 °C. This is performed through different thermomechanical processing routes (different ARB cycles at different temperatures of 350-200 °C). The microstructures and mechanical properties were investigated. The results indicate that significant grain refinement is observed after the first two cycles at the highest ARB temperature as a result of dynamic recrystallization, which is necessary for the subsequently ARB cycles at relatively lower temperature with the aim to restrict grain growth. No significant finer grain size was observed through the fifth and sixth cycles while the microstructure homogeneity is further improved. The grain structure can be effectively refined at lower ARB processing temperature and higher cycles. The resulting material exhibited high strength and relatively high ductility at ambient temperature when ARB deformed above 250 °C. The mechanical properties of the ARB deformed materials are strongly dependent on several main factors: the amount and the homogeneity of strain achieved, grain size and microstructure homogeneity, textures developed during ARB and interface bonding quality.     

HOMOGENIZATION TREATMENT OF Mg-Al-Zn(MM)MAGNESIUM ALLOY INGOTS

The Mg-Al-Zn series AZ31 and AZ31 MM alloys are homogenized at 673, 723 and 753K respectively. The hardness of alloy ingots at different heat-treated states is measured and the micro structures are observed. The optimum annealing temperature is 723K and the time is 12h.     

Effect of inter-cycle heat treatment in accumulative roll-bonding (ARB) process on planar isotropy of mechanical properties of AA1050 sheets

The accumulative roll-bonding (ARB) process was applied on the strips of aluminum alloy 1050 in two processing conditions: cold ARB and warm ARB. The results of tensile tests and microhardness measurement show that the warm ARB process exhibits the lower tensile strength and microhardness, more homogeneous distribution of the microhardness, higher elongation, and especially superior planar isotropy of the tensile properties in comparison to the cold ARB, because of the intermediate heat treatment as well as the elevated temperature rolling in the warm ARB process. Furthermore, with increasing the cycles of both processes, the planar isotropy decreases progressively.     

锛造Mg-Al-Zn合金的成分、相组成与凝固路径的关系

采用SEM,EDS和XRD研究了几种Mg-Al-Zn合金的成分、相组成与凝固路径的关系.结果表明,Mg-Al-Zn合金的相组成与Zn/Al质量比有关;随着Zn/Al比值的增加,第二相γ Mg_(17)Al_(12)的数量减少,逐渐被φ-Mg_(21)(Zn,Al)_(17)取代,直至完全消失.通过搜集合金中町能存在的各相的热力学模型,运用Pandat热力学计算软件平台,计算并比较了平衡和非平衡(Scheil模型及金属型铸造)条件下合金的成分、相组成与凝固路径的关系.结果表明,金属型铸造的凝固过程偏离平衡凝固过程,Scheil模饿很好地解释了大多数合金铸造组织的相组成;但是由于Scheil模型不考虑有同相作为反应物参与的包晶反应,对ZA65合金凝固路径和相组成的预测结果与实际铸造组织的柑组成不符.     

Formation of nano-sized grains in Cu and Cu−Fe−P alloys by accumulative roll bonding process

Mechanical properties and formation of nano-sized grains in Cu and Cu−Fe−P alloys by the accumulative roll bonding (ARB) process were investigated. Nano-sized grains were successfully obtained in OFC and PMC-90 alloys by the ARB process after the third cycle. Once the 200 nm grains formed, further reduction in the grain size was not observed up to 8 ARB process cycles. For both alloys, the tensile strength values increased drastically in the initial stage of the ARB process. The tensile strength values of both alloys tended to saturate after the third ARB process cycle. The tensile elongation value greatly decreased by 1 cycle of the ARB process due to the strain hardening. After the third cycle of the ARB process, each alloy showed a gradual increase in tensile elongation due to the dynamic recovery. For PMC-90 alloy, the strength value was higher than that of OFC due to addition of the alloying elements. With increased annealing temperature, the nanosized grains tended to grow in OFC at 150°C, and after annealing at 200°C, coarse grains formed. On the other hand, in PMC-90 alloy, there was no grain growth up to 250°C due to the alloying elements (Fe, P).     

钇及混合稀土对镁铝锌合金组织与性能的影响

探讨了钇和混合稀土对不同铝锌比的镁铝锌合金的显微组织、时效析出以及常温拉伸性能的影响。添加稀土元素之后，镁铝锌合金的铸态组织得到细化，并在显微组织中形成铝的稀土相；合金的时效峰值稍有提高，时效峰值的出现时间因为稀土元素的添加而有所滞后。添加稀土元素使镁合金的室温拉伸性能得到提高。     

The combined effect of aging and accumulative roll bonding on the evolution of the microstructure and mechanical characteristics of an Al–0.2 wt % Zr alloy

This work is devoted to the effect of processes initiated by the combined action of aging (A) and accumulative roll bonding (ARB) on the evolution of the microstructure and the mechanical characteristics of an Al–0.2 wt % Zr alloy. Upon solution treatment (ST), followed by aging at temperatures of 350 and 450°C, the specimens were subjected to deformation to a degree of deformation of 80% using ARB. The evolution of the microstructure was examined using atomic force microscopy and the mechanical characteristics of the specimens were determined using tensile tests and Vickers microhardness measurements. The results have shown that, upon ten ARB cycles, the grain size decreased to 0.3, 0.4, and 0.32 μm in the specimens subjected to ST followed by ARB (ST–ARB), ST followed by A at a temperature of 350°C and ARB (350°C–A–ARB), and ST followed by A at a temperature of 450°C and ARB (450°C–A–ARB), respectively. This study has also shown that the combined use of preliminary A and subsequent ARB holds promise in enhancing the mechanical characteristics of the alloy due to precipitates that appear in the course of annealing. Fracture surfaces of the rolled specimens subjected to the tensile tests were examined using scanning electron microscopy. The results of these examinations have shown that in the specimens subjected to ST followed by ARB brittle fracture has been observed at the stage of the final ARB cycles, while in the A–ARB specimens cleavage facets (sites of fracture over the cleavage plane) and river lines have appeared on the fracture surfaces.     

Mechanical properties of ultrafine grained 5052 Al alloy produced by accumulative roll-bonding and cryogenic rolling

Mechanical properties in conjunction with microstructural evolution during annealing of 5052 Al alloy deformed at cryogenic temperature were investigated and compared with those yielded by the ARB process. ARB was conducted up to 7 cycles under conditions where the reduction in thickness per cycle was 50% and the rolling temperature was 300°C. To investigate the effect of annealing temperature, cryo-rolled sheets with 85% reduction were annealed in a temperature range of 150≈300°C for one hour. Strengths of 5052 Al alloy ARB processed at 300°C increased with increasing number of cycles and decreased rapidly after 6 or 7 cycles. This indicated that, during the ARB process, work hardening proceeded at low strains and subdivision of grains and dynamic recovery occurred at high strains. Tensile strength and yield strength of cryo-rolled 5052 Al alloy decreased as the annealing temperature increased. The volume fraction of recrystallized and coarsened grains appeared to have the most significant influence on strength and ductility in sheets annealed at 250°C.     

Precipitation behavior of Mg17Al12 in monolithic and Al2O3 short fiber reinforced Mg-Al-Zn alloys

The precipitation behavior of Mg₁₇Al₁₂ in monolithic and Al₂O₃ short fiber reinforced Mg-Al-Zn alloys was investigated by optical and transmission electron microscopies and hardness measurements. The maximum hardness was obtained when the long and short axes of the platelet type continuous Mg₁₇Al₁₂ precipitates were about 0.3 μm and 0.04 μm, respectively. The area fraction of the discontinuous Mg₁₇Al₁₂ precipitate nodule reached about 0.23. The coarsening behavior of the discontinuous Mg₁₇Al₁₂ precipitate nodule was found to obey the relationship suggested by the Johnson-Mehl-Avrami model. The slope of the Johnson-Mehl-Avrami plot for the Al₂O₃ short fiber reinforced Mg-Al-Zn alloy was four times larger than that for the monolithic alloy due to the increased number of nucleation sites, i.e. nucleation at the interface between the reinforcing material and the α-Mg matrix as well as at the α-Mg grain boundaries.     

AZ91D镁合金表面覆铝的显微组织及性能

在大气环境中、恒定压力作用下,使用镁铝共晶合金粉末作为连接剂在AZ91D镁合金表面进行覆铝处理.利用扫描电子显微镜分析了铝箔与镁合金结合界面的显微组织结构,通过电化学腐蚀试验及球盘磨损试验对覆铝试样表面的耐腐蚀性和耐磨性进行了测试.结果表明,结合界面由Al_3Mg_2层、Mg_(17)Al_(12)层、镁铝共晶层、镁铝锌化合物层组成,覆铝后试样的耐蚀性、耐磨性较AZ91D镁合金均有提高.     

Enhanced Electromagnetic Interference Shielding in a Duplex-Phase Mg-9Li-3Al-1Zn Alloy Processed by Accumulative Roll Bonding

High electromagnetic shielding performance was achieved in the Mg-9Li-3Al-1Zn alloy processed by accumulative roll bonding(ARB).The microstructure,electromagnetic interference shielding effectiveness(SE) in the frequency of 30-1500 MHz and mechanical properties of the alloy were investigated.A model based on the shielding of the electromagnetic plane wave was used to theoretically discuss the EMI shielding mechanisms of ARB-processed alloy.Results indicate that the SE of the material increases gradually with the increase in the ARB pass.The enhanced SE can be attributed to the obvious microstructure orientation caused by ARB,and the alternative arrangement of alpha(Mg) phase and beta(Li)phase.In addition,with the increase in ARB pass,the number of interfaces between layers increases and the grain orientation of each layer tends to alignment along c-axis,which is beneficial to the reflection loss and multiple reflection loss of the incident electromagnetic wave.     

Discharge performance of Mg-Al-Pb-La anode for Mg-air battery

The discharge performance of Mg-Al-Pb-La anode was investigated by electrochemical techniques and compared with that of Mg-Al-Pb alloy. The results indicate that the Mg-Al-Pb-La anode provides enhanced corrosion resistance at open circle potential, and exhibits better discharge activity than the Mg-Al-Pb alloy. The utilization efficiency of Mg-Al-Pb-La anode is higher than that of commercial Mg-Al-Zn (AZ) and Mg-Al-Mn (AM) alloys. A single Mg-air battery with Mg-Al-Pb-La alloy as the anode and air as the cathode has an average discharge potential of 1.295 V and a discharge capacity of 1370 mA·h/g during discharge at 10 mA/cm², which is higher than that of batteries using Mg-Li anodes. The enhancement in discharge performance of the Mg-Al-Pb-La anode is caused by its modified microstructure, which reduces the self-corrosion and accelerates the spalling of oxidation products during battery discharge. Furthermore, the dissolution mechanism of Mg-Al-Pb-La anode during the discharge process was analyzed.     

Effects of ARB and ageing processes on mechanical properties and microstructure of 6061 aluminum alloy

Accumulative roll bonding (ARB) has been used as a severe plastic deformation process for the production of high-strength materials. Ageing treatment has been found to enhance the strength of alloys by precipitation of a second phase. In the present work, ARB followed by the ageing process was used for the fabrication of the high-strength 6061 aluminum alloy. Samples of the alloy thus made were subjected under annealed and ARBed conditions to ageing treatment at different temperatures for different times and their mechanical properties were evaluated. It was found that the microhardness and tensile strength of the specimens increased with the number of ARB cycles but their elongation values decreased. After the ageing treatment, the mechanical properties of the ARBed specimens improved in terms of both strength and ductility. Based on TEM observations, it may be concluded that the improved mechanical properties after the duplex ARB-ageing process can be attributed to the precipitation of very fine particles with a slight decrease in dislocation density and limited structure coarsening. SEM observation of fracture surfaces of aged specimens indicated that the fracture was predominantly caused by microvoid coalescence at constituent particles.     

Anodization of Mg-alloy AZ91 in NaOH solutions

Anodic oxide films were grown on the Mg-Al-Zn alloy AZ91 in NaOH-solution and examined by electron microscopy, X-ray diffraction and micro-Raman spectroscopy. The anodic film consists of an inner barrier layer and an outer porous layer. The thin barrier layer is hydrated or contains Mg(OH)₂. The porous layer was identified as crystalline MgO (periclase) and contains tunnels formed by breakdown/repair events, which involve plasma-electrolytic reactions. The micro-Raman-spectrum indicates the formation of a highly disordered zone around the tunnels. Applied current density, potential limit, electrolyte concentration and alloy phase were identified as parameters which have an influence on density and diameter of the tunnels.     

累积叠轧焊AZ31镁合金微观组织和织构演变的EBSD研究

对AZ31镁合金热轧板在350℃进行了累积叠轧焊(ARB)变形,采用EBSD技术研究了AZ31镁合金的微观组织和织构演变.结果表明,ARB可以显著细化AZ31镁合金的晶粒组织,经过3道次变形后平均晶粒尺寸为2.18μm,后续的ARB变形使AZ31镁合金的微观组织更均匀,但晶粒不会再显著细化,说明存在临界ARB变形道次,使晶粒细化和晶粒长大之间达到动态平衡.AZ31镁合金在ARB变形过程中的晶粒细化机制为连续动态再结晶,尤其还观察到了旋转动态再结晶.动态再结晶的形变储存能来源于多道次累积的剧烈应变和沿厚度方向分布复杂的剪切变形.ARB变形过程中旋转动态再结晶和剪切变形使新晶粒c轴发生旋转,导致基面织构弱化.     

On the chloride-induced pitting of ultra fine grains 5052 aluminum alloy produced by accumulative roll bonding process

Pitting corrosion susceptibility of ultra fine grain (UFG) 5052 aluminum alloy (AA 5052) sheets highly deformed by accumulative roll-bonding (ARB) was investigated in 3.5 wt% NaCl solution using potentiodynamic polarization, cyclic voltammetry and immersion tests. The morphology of localized attacks was analyzed by SEM-EDS. Pitting corrosion resistance of samples was diminished with increasing the number of ARB passes which is presumably due to microstructure refinement and increasing the defect density.     

Pre-aging time dependence of microstructure and mechanical properties in nanostructured Al-2wt%Cu alloy

This work is focused on the effect of pre-aging time on the properties of Al-2wt%Cu alloy processed by accumulative roll bonding (ARB) process. Following aged at 190 °C for 10 or 30 min, the samples were deformed up to a strain of 4.8 by the ARB process. The microstructure evolution was investigated by transmission electron microscope and electron backscattering diffraction analyzes. The results showed that the Al₂Cu precipitates were formed with different sizes due to the different pre-aging times and the finer precipitates were more effective on the formation of high angle grain boundaries during the ARB process. The grain size of Aged-10 min and Aged-30 min specimens decreased to 400 nm and 420 nm, respectively, after 6 cycles of the ARB process. Also, the final texture after 6 cycles of the ARB process, shown in the {111} pole figure, were different depending on the starting microstructures. The mechanical properties of specimens were investigated by the Vickers microhardness measurements and the tensile tests. The results showed that the mechanical properties are affected by the starting microstructure. The mechanical properties of Aged-10 min specimen were different compared to Aged-30 min specimen due to the different size of the pre-existing precipitates. Although by continuing process, the precipitates were probably dissolved due to the heavy deformation.     

Passive Behavior of Ultra-Fine-Grained 1050 Aluminum Alloy Produced by Accumulative Roll Bonding in a Borate Buffer Solution

In this study, the effect of the ARB process on the passive behavior of ultra-fine-grained 1050 aluminum alloy in a borate buffer solution(p H 6.0) has been investigated. The result of the microhardness tests revealed that the microhardness values increase with an increasing number of ARB cycles. The potentiodynamic polarization plots revealed that the higher number of cycles for the specimens proceeds with the ARB process rather than annealing yield to lower corrosion and passive current densities and more noble corrosion potential values. Moreover, electrochemical impedance spectroscopy measurements showed that increasing the number of ARB cycles offers better conditions for forming the passive films.