热挤压对铸态Mg-1Zn-0.3Zr-1Y-2Sn镁合金组织和性能的影响（英文）

通过光学显微镜(OM)、扫描电镜(SEM)、浸泡实验、析氢实验、电化学试验、拉伸试验等方法,研究了不同挤压温度(340、360、380、400℃)下,热挤压对铸态Mg-1Zn-0.3Zr-1Y-2Sn合金组织和性能的影响。结果表明:热挤压后,合金的第二相沿挤压方向破碎成颗粒,微观组织中存在动态再结晶和变形晶粒。随着挤压温度的升高,第二相的含量变化较小,动态再结晶晶粒尺寸逐渐增大。热挤压后,合金的力学性能得到改善,但其耐腐蚀性最终减弱。热挤压处理可以在腐蚀的早期阶段提高合金的耐腐蚀性能,但随着腐蚀的进行,在后期合金的耐蚀性能会降低。当热挤压温度为360℃时,合金具有较好的力学性能和耐腐蚀性能。     

Study of the corrosion and microstructure with annealing conditions of a β-quenched HANA-4 alloy

The variation of microstructure and corrosion characteristics with the applied annealing conditions of a HANA-4 (Zr-1.5Nb-0.4Sn-0.2Fe-0.1Cr) alloy were studied by utilizing transmission electron microscopy and a corrosion test at 360 °C in a water environment. The samples were annealed at temperature ranges from 540 to 660 °C up to 16 h after β quenching at 1050 °C. The corrosion behaviour with the annealing conditions was divided into two groups following the second phase characteristics. The suitable annealing temperature to obtain good corrosion resistance in the HANA-4 alloy ranged from 570 to 600 °C.     

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.     

Corrosion behaviour of magnesium/aluminium alloys in 3.5 wt.% NaCl

Corrosion behaviour of commercial magnesium/aluminium alloys (AZ31, AZ80 and AZ91D) was investigated by electrochemical and gravimetric tests in 3.5 wt.% NaCl at 25 °C. Corrosion products were analysed by scanning electron microscopy, energy dispersive X-ray analysis and low-angle X-ray diffraction. Corrosion damage was mainly caused by formation of a Mg(OH)₂ corrosion layer. AZ80 and AZ91D alloys revealed the highest corrosion resistance. The relatively fine β-phase (Mg₁₇Al₁₂) network and the aluminium enrichment produced on the corroded surface were the key factors limiting progression of the corrosion attack. Preferential attack was located at the matrix/β-phase and matrix/MnAl intermetallic compounds interfaces.     

Microstructure and corrosion performance of a cold sprayed aluminium coating on AZ91D magnesium alloy

A pure Al coating was deposited on AZ91D magnesium alloy through cold spray (CS) technique. The microstructure of the coating was characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that the grain interfaces and subgrains formed close to the particle/particle boundaries. Electrochemical tests revealed that the cold sprayed pure Al coating had better pitting corrosion resistance than bulk pure Al with similar purity in neutral 3.5 wt.% NaCl solution. In addition, a mass-transfer step was found to be involved in the corrosion during 10 days immersion.     

Effect of grain size and twins on corrosion behaviour of AZ31B magnesium alloy

Grain refining is a promising approach to improve mechanical properties of magnesium alloys, but how grain size and twins affect corrosion behaviour is not well understood. In this work, corrosion resistance of AZ31B alloy with different grain sizes is studied in 3.5% NaCl solution using immersion testing, evolved hydrogen gas measurement and potentiodynamic polarisation measurement. Intra-granular corrosion was predominant and the existence of twins further accelerated the corrosion. The effect of grain size was more pronounced in the corrosion of the untwinned microstructure. The corrosion rate significantly increased as the average grain size increased from 65 to 250 μm.     

Corrosion of hot extrusion AZ91 magnesium alloy: I-relation between the microstructure and corrosion behavior

The effect of hot extrusion on the corrosion behavior of AZ91 magnesiun alloy was investigated by weight loss, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. The results showed that the extruded alloy had lower corrosion resistance compared to cast alloy. This observation has been explained from point of view of microstructure changes, wherein the increased density of dislocation, twins and grain boundary increased the anodic dissolution of AZ91 alloy and rearrangement of β phase accelerated the rate of both the anodic and cathodic process.     

Thixoforming of EN AW-2014 alloy at high solid fraction

EN AW-2014 extruded alloy slugs were thixoformed at 615 °C where the solid fraction is estimated to be 80%. The recrystallization process occurred during heating to the thixoforming temperature, between 550 °C and 600 °C, well above the solidus temperature owing to the pinning of grain boundaries by Al₂Cu precipitates. The equiaxed polygonal grains thus obtained have become increasingly globular upon soaking. Si was enriched in the grain boundaries during soaking while the solid solution matrix was gradually depleted off Cu. The grain boundary composition has moved closer to that of the Al-Cu-Si ternary eutectic with a lower melting point than the binary Al-Cu eutectic, facilitating grain boundary melting. The liquid phase has then penetrated between the grains, forming a more or less continous intergranular network. Microstructural features essential for forming in the semi-solid state were obtained after about 10 min at 615 °C. The subsequent forming process has occurred in the semi-solid state with no evidence of grain deformation. The thixoformed EN AW-2014 part was solutionized at 500 °C for 2 h and was subsequently quenched in water. Artificial ageing at 160 °C has produced hardness values as high as 160 HV after only 8 h. It is concluded that the high strength wrought EN AW-2014 alloy feedstock processed by the RAP route respond to a thixoforming operation in a very favorable fashion.     

Corrosion and recession behavior of zircon in water vapor environment at high temperature

A corrosion test in static state water vapor environment and a recession test in high velocity steam jet environment for zircon bulk were performed at 1300 °C. The trace of the water vapor corrosion could be recognized on the grain surfaces and at the grain boundaries for the sample after the static state corrosion test. Sand ripple like morphology was generated on the grain surfaces and etch pits with less than 0.1 μm size were formed at the grain boundaries. A porous structure was formed on the bulk surface of the sample after the steam jet test. A glassy phase enriched with silica could be recognized on the surface of the sample after the test. Cracks were induced on the bulk surface during the test. The zircon phase at the bulk surface decomposed into monoclinic zirconia phase and the fraction of silica component at the bulk surface decreased by the steam jet test. The monoclinic zirconia phase was observed to re-generate and grow on the bulk surface.     

Effect of heat treatment on corrosion behaviour of magnesium alloy AZ91D in simulated body fluid

The research explored ways of improving corrosion behaviour of AZ91D magnesium alloy through heat treatment for degradable biocompatible implant application. Corrosion resistance of heat-treated samples is studied in simulated body fluid at 37 °C using immersion and electrochemical testing. Heat treatment significantly affected microgalvanic corrosion behaviour between cathodic β-Mg₁₇Al₁₂ phase and anodic α-Mg matrix. In T4 microstructure, dissolution of the β-Mg₁₇Al₁₂ phase decreased the cathode-to-anode area ratio, leading to accelerated corrosion of α-Mg matrix. Fine β-Mg₁₇Al₁₂ precipitates in T6 microstructure facilitated intergranular corrosion and pitting, but the rate of corrosion was less than those of as-cast and T4 microstructures.     

Electrochemical corrosion behaviour of nanotubular Ti-13Nb-13Zr alloy in Ringer’s solution

Nanotubular oxide layer formation was achieved on biomedical grade Ti-13Nb-13Zr alloy using anodization technique in 1 M H₃PO₄ + 0.5 wt.% NaF. The as-formed and heat treated nanotubes were characterized using SEM, XRD and TEM. Corrosion behaviour of the nanotubular alloy was investigated employing potentiodynamic and potentiostatic polarization. The alloy after nanotubular oxide layer formation exhibited significantly higher corrosion current density than the bare alloy. The lower corrosion resistance of the nanotubular alloy was suggested to be associated with the distinctly separated barrier oxide/concave shaped tube bottom interface. A heat treatment at 150 °C appreciably enhanced the corrosion resistance property.     

Preliminary investigations on the Mg–Al–Zn/Al laminated composite fabricated by equal channel angular extrusion

In order to utilize the advantage of low density and overcome the disadvantages of poor corrosion resistance and low strength, the laminated composites of Mg alloys fabricated by different methods have attracted extensively attentions. In this paper, the equal channel angular extrusion (ECAE), which has been widely used to fabricate ultrafine grain bulk materials, was introduced to fabricate the Mg–3Al–1Zn/Al (AZ31/Al) laminated composites at different temperatures. After fabrication and annealing treatment at different temperatures, the microstructural evolution and phase constitution near the joining interface of AZ31/Al composites were evaluated using optical and scanning electron microscope as well as X-ray diffraction (XRD). The results indicated that the higher annealing temperature promoted the formations of thicker bonding layers and more reaction phases near the joining interface, which mainly included Mg₂Al₃ and Mg₁₇Al₁₂ phases. The AZ31/Al laminated composite fabricated at 300 °C revealed thicker diffusion layer than that fabricated at 200 °C after anneal under the same condition, and the appropriate technological parameters of fabricating AZ31/Al laminated composites were also discussed.     

Corrosion behaviour of silicon-carbide-particle reinforced AZ92 magnesium alloy

The corrosion behaviour of silicon-carbide-particle (SiCp) reinforced AZ92 magnesium alloy manufactured by a powder metallurgy process was evaluated in 3.5 wt.% NaCl solution, neutral salt fog (ASTM B 117) and high relative humidity (98% RH, 50 °C) environments. The findings revealed severe corrosion of AZ92/SiC/0-10p materials in salt fog environment with formation of corrosion products consisting of Mg(OH)₂ and (Mg,Al)_x(OH)_y. The addition of SiCp increased the corrosion rate and promoted cracking and spalling of the corrosion layer for increasing exposure times. Composite materials revealed higher corrosion resistance in high humidity atmosphere with almost no influence of SiCp on the corrosion behaviour.     

Corrosion behavior of iron-based alloys in the LiBr + ethylene glycol + H2O mixture

The corrosion resistance of 1018 carbon steel, 304 and 316 type stainless steels in the LiBr (55 wt.%) + ethylene glycol + H₂O mixture at 25, 50 and 80 °C has been studied using electrochemical techniques which included potentiodynamic polarization curves, electrochemical noise and electrochemical impedance spectroscopy techniques. Results showed that, at all tested temperature, the three steels exhibited an active-passive behavior. Carbon steel showed the highest corrosion rate, since both the passive and corrosion current density values were between two and four orders of magnitude higher than those found for both stainless steels. Similarly, the most active pitting potential values was for 1018 carbon steel. For 1018 carbon steel, the corrosion process was under a mixed diffusion and charge transfer at 25 °C, whereas at 50 and 80 °C a pure diffusion controlled process could be observed. For 316 type stainless steel, at 25 and 50 °C a species adsorption controlled process was observed, whereas at 80 °C a diffusion controlled mechanism was present. Additionally, at 25 °C, the three steels were more susceptible to uniform type of corrosion, whereas at 50 and 80 °C they were very susceptible to localized type of corrosion.     

Influence of chloride ion concentration and temperature on the corrosion of Mg-Al alloys in salt fog

The influence of temperature and chloride concentration on the corrosion behaviour of Mg-Al alloys exposed to salt fog was evaluated. Corrosion attack increased with decreasing aluminium content in the alloy and increasing Cl⁻ concentration and temperature. The effect of Al-Mn inclusions, which revealed several stoichiometries and were up to 300 mV more noble than the magnesium matrix, was only noticeable in the early stages of corrosion of the AZ31 alloy. Aluminium segregation and β-phase distribution were the main controlling factors for the AZ80 and AZ91D alloys, the latter being more susceptible to variations in the saline concentration.     

Baking treatment effect on materials characteristics and electrochemical behavior of anodic film formed on AZ91D magnesium alloy

The composition and microstructure of the anodic films formed on AZ91D Mg alloy, with or without baking, were investigated. The associated corrosion behavior of the anodized alloy in 3.5 wt% NaCl solution was also examined using electrochemical impedance spectroscopy (EIS). The results show that MgO was the main component in the anodic film which also contained some Mg(OH)₂, Al₂O₃, Al(OH)₃, and MgAl₂O₄. Both the amorphous and crystalline forms of anodic film were identified. The degree of crystallinity depended on baking temperature, which increased with increasing temperature in the range of 50-250 °C. The amounts of MgO and Al₂O₃ increased as a result of a dehydration reaction. The polarization resistance of anodized Mg alloy was improved significantly by increasing the oxide content in the anodic film. An optimum value of polarization resistance of anodic film was obtained for the alloy baked at 150 °C for 2 h followed by air cooling.     

Corrosion resistance of Al ion implanted AZ31 magnesium alloy at elevated temperature

The Al ion implantation into AZ31 magnesium alloy was carried out in a MEVVA 80-10 ion implantation system at an ion energy of 40-50 keV with an ion implantation dose ranging from 2 × 10¹⁶ to 1 × 10¹⁷ ions/cm² at an elevated temperature of 300 °C induced by an ion current density of 26 μA/cm². The concentration-depth profile of implanted Al in AZ31 alloy measured by Rutherford backscattering spectrometry (RBS) is a Gaussian-type-like distribution in a depth up to about 1200 nm with the maximum Al concentration of about 8 at.%. The X-ray diffraction (XRD) analysis revealed the formation of α-Mg(Al) phase, intermetallic β-Mg₁₇Al₁₂, and MgO phase on the Al ion implanted samples. The potentiodynamic anodic polarization curves of the Al ion implanted samples in the 0.01 mol/l NaCl solution with a pH value of 12 showed increases of the corrosion potential and the pitting breakdown potential, and a decrease of the passive current density, respectively. The Al ion implanted samples with 6 × 10¹⁶ ions/cm² achieved the high pitting breakdown potential to about − 480 mV (SCE). In the 0.08 mol/l NaCl solution with pH = 12, the Al ion implanted samples with 1 × 10¹⁷ ions/cm² showed an increased pitting breakdown potential to about − 1290 mV (SCE), from around − 1540 mV (SCE) of unimplanted samples. It is indicated that different corrosion mechanisms are responsible for improvement in corrosion resistance of the AZ31 magnesium alloy in the NaCl solutions with the varied concentrations.     

Corrosion study of HK-40m alloy exposed to molten sulfate/vanadate mixtures using the electrochemical noise technique

Corrosion performance of HK-40m alloy obtained from electrochemical noise technique and polarization curves during 24 h of exposure in high sulfate (80 mol% Na₂SO₄-20 mol% V₂O₅) and high vanadate (80 mol% V₂O₅-20 mol% Na₂SO₄) molten salts at 700 °C are reported. Electrochemical noise signals were analyzed in the time and frequency domain. A statistical analysis obtaining the resistance noise, the current standard deviation and the localization index are presented as well as the determination of corrosion rates. Corrosion rates were supported by X-ray diffraction analysis of corrosion products and scanning electron microscopy analysis of corroded samples. Results from optical microscope examination of the corroded samples showed that HK-40m alloy suffered inter-granular corrosion when was exposed to the high vanadate salt, whereas exposed to the high sulfate salt, HK-40m corroded through a mixed corrosion process. A corrosion mechanism of HK-40m alloy was obtained together with the corrosion rate, showing the different behavior when exposing the alloy to a high vanadate and high sulfate molten salts.     

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。     

Pitting behavior of a bulk Ni-18 wt.% Fe nanocrystalline alloy

Three electrodeposited Ni-18 wt.% Fe samples were annealed at 400 °C for 3 h (hrs), 8 h, and 24 h to study the effects of grain size on the electrochemical properties of bulk Ni-18 wt.% Fe in 3.5 wt.% NaCl. The electrochemical results from the annealed samples are compared with those measured for the as-received Ni-18 wt.% Fe material consisting of an average grain size of 23 nanometers (nm). Of the four materials studied, the as-received nanocrystalline alloy less sensitive to localized corrosion.