Laurus nobilis L. oil as green corrosion inhibitor for aluminium and AA5754 aluminium alloy in 3% NaCl solution

The influence of (30%, v/v) ethanolic solution of Laurus nobilis L. oil on the corrosion inhibition of aluminium and AA5754 aluminium alloy in 3% NaCl solution was studied by weight loss method, potentiodynamic polarization, and linear polarization method. The polarization measurements show that addition of this oil in concentrations ranging from 10 ppm to 50 ppm induces a decrease of cathodic currents densities. The results confirm that AA5754 alloy has better corrosion resistance in 3% NaCl solution than pure aluminium, while the oil investigated has better inhibition action on corrosion process of pure aluminium. The surface analysis via SEM techniques indicate that the active molecules from L. nobilis L. oil absolutely retard the pitting corrosion on the specimen surfaces.     

Influence of the supersaturated silicon solid solution concentration on the effectiveness of severe plastic deformation processing in Al-7 wt.% Si casting alloy

A comparative study of room temperature severe plastic deformation (SPD) of a hypoeutectic Al-7 wt.% Si casting alloy by high pressure torsion (HPT) and equal channel angular pressing (ECAP) has been performed. Microstructural parameters and microhardness were evaluated in the present work. Three different initial Si solid solution contents have been considered: as cast (C sample, 1.6 wt.% Si), annealed and quenched (Q sample, 1.2 wt.% Si) and annealed and furnace cooled (S sample, 0.7 wt.% Si). The samples processed by ECAP have smaller average Si particle sizes (0.9-1.7 μm), than those for samples processed by HPT (2.4-4.4 μm). The initial supersaturated Si solid solution is the major factor affecting the microstructure and the mechanical properties of the material. Fine deformation-induced Si precipitates from the supersaturated solid solution were responsible of the large grain refinement obtained by both SPD processing methods, which was considerably higher than that reported for pure aluminium. Q samples, processed by both SPD methods, containing an intermediate concentration of Si in solid solution, show the highest hardness due to the finest and most homogeneous microstructure. The finest and homogeneous grain size was ∼0.2 μm for the HPTed and ∼0.4 μm for the ECAPed Q samples.     

Relationship between microstructure,hardness and corrosion resistance in 20 wt.%Cr, 27 wt.%Cr and 36 wt.%Cr high chromium cast irons

The microstructures, hardness and corrosion behavior of high chromium cast irons with 20, 27 and 36 wt.%Cr have been compared. The matrix in as-cast 20 wt.%Cr, 27 wt.%Cr and 36 wt.%Cr high chromium cast irons is pearlite, austenite and ferrite, respectively. The eutectic carbide in all cases is M₇C₃ with stoichiometry as (Cr_3.37, Fe_3.63)C₃, (Cr_4.75, Fe_2.25)C₃ and (Cr_5.55, Fe_1.45)C₃, respectively. After destabilization at 1000 °C for 4 h followed by forced air cooling, the microstructure of heat-treatable 20 wt.%Cr and 27 wt.%Cr high chromium cast irons consisted of precipitated secondary carbides within a martensite matrix, with the eutectic carbides remaining unchanged. The type of the secondary carbide is M₇C₃ in 20 wt.%Cr iron, whereas both M₂₃C₆ and M₇C₃ secondary carbides are present in the 27 wt.%Cr high chromium cast iron. The size and volume fraction of the secondary carbides in 20 wt.%Cr high chromium cast iron were higher than for 27 wt.%Cr high chromium cast iron. The hardness of heat-treated 20 wt.%Cr high chromium cast iron was higher than that of heat-treated 27 wt.%Cr high chromium cast iron. Anodic polarisation tests showed that a passive film can form faster in the 27 wt.%Cr high chromium cast iron than in the 20 wt.%Cr high chromium cast iron, and the ferritic matrix in 36 wt.%Cr high chromium cast iron was the most corrosion resistant in that it exhibited a wider passive range and lower current density than the pearlitic or austenitic/martensitic matrices in 20 wt.%Cr and 27 wt.%Cr high chromium cast irons. For both the 20 wt.%Cr and the 27 wt.%Cr high chromium cast irons, destabilization heat treatment gave a slight improvement in corrosion resistance.     

Effect of frequency on fatigue crack growth behavior of magnesium alloy AZ61 under immersed 3.5 mass% NaCl environment

Fatigue crack growth test of AZ61 magnesium alloy was carried out under immersed NaCl environment at frequencies of 15, 5 and 0.5 Hz under a stress ratio of 0.1. In order to investigate the effect of frequency on fatigue crack growth behavior in detail, additional tests at frequencies ranged from 15 to 0.01 Hz were conducted under a constant ΔK of 3.25 MPa m^1/2. Effect of frequency was clearly observed in low ΔK region, where fatigue crack growth rate decreased with decreasing frequency. Crack closure would be a dominant factor for the frequency effect observed under immersed NaCl environment at frequencies ranged from 15 to 0.5 Hz. However, fatigue crack growth rates at frequencies lower than 0.05 Hz were higher than those at frequencies higher than 0.5 Hz. The accelerated fatigue crack growth rates at frequencies lower than 0.05 Hz would be attributed to the corrosion attack at the crack tip.     

Annealed microstructure dependent corrosion behavior of Ti-6Al-3Nb-2Zr-1 Mo alloy

Corrosion resistance of titanium(Ti)alloys is closely connected with their microstructure which can be adjusted and controlled via different annealing schemes.Herein,we systematically investigate the specific effects of annealing on the corrosion performance of Ti-6 Al-3 Nb-2 Zr-1 Mo(Ti80)alloy in 3.5 wt.%NaCl and 5 M HCl solutions,respectively,based on open circuit potential(OCP),potentiodynamic polarization,electrochemical impedance spectroscopy(EIS),static immersion tests and surface analysis.Results indicate that increasing annealing tempe rature endows Ti80 alloy with a higher volume fraction ofβphase and finerαphase,which in turn improves its corrosion resistance.Surface characterization demonstrates thatβphase is more resistant to corrosion thanαphase owing to a higher content of Nb,Mo,and Zr in the former;additionally,the decreased thickness of a phase alleviates segregation of elements to further restrain the micro-galvanic couple effects betweenαandβphases.Meanwhile,the influential mechanisms of environmental conditions on corrosion of Ti80 alloy are discussed in detail.As the formation of a highly compact and stable oxide film on surface,annealed Ti80 alloys exhibit a low corrosion current density(10^-6A/cm²)and high polarization impedance(10⁶Ω·cm²)in 3.5 wt.%NaCl solution.However,they suffer severe corrosion in 5 M HCl solution,resulting from the breakdown of native oxide films(the conversion of TiO₂to aqueous Ti³⁺),active dissolution of substrate Ti to aqueous Ti³⁺and existence of micro-galvanic couple effects.Those findings could provide new insights to designing Ti alloys with high-corrosion resistance through microstructural optimization.     

The corrosion behavior of Ti-6Al-3Nb-2Zr-1Mo alloy: Effects of HCl concentration and temperature

Investigation about the corrosion behavior of Ti alloys in different ambient environment is of great significance for their practical application.Herein,we systematically investigate the corrosion behavior of a newfound Ti-6Al-3Nb-2Zr-1 Mo (Ti80) alloy in hydrochloric acid (HCI) ranging from 1.37 to 7 M,and temperature ranging from 25 to 55 ℃,by means of electrochemical measurements,static immersion tests and surface analysis.Results manifest that increasing either HCI concentration or temperature can accelerate the corrosion of Ti80 alloy via promoting the breakdown of native protective oxide film and then further facilitating the active dissolution of Ti80 matrix.According to potentiodynamic polarization curves,Ti80 alloy displays a spontaneous passive behavior in 1.37 M HCI at 25 ℃,compared to a typical active-passive behavior under the other conditions.As indicated by cathodic Tafel slope,the rate determining step for cathodic hydrogen evolution reaction is likely the discharge reaction step.The apparent activation energies obtained from corrosion current density and maximum anodic current density for Ti80 alloy in 5 M HCI solution are 62.4 and 55.6 kJ mol-1,respectively,which signifies that the rate determining step in the corrosion process of Ti80 alloy is mainly determined by surface-chemical reaction rather than diffusion.Besides,the electrochemical impedance spectroscopy tests demonstrate that a stable and compact oxide film exists in 1.37 M HCl at 25 ℃,whereas a porous corrosion product film forms under the other conditions.Overall,the critical HCI concentration at which Ti80 alloy can maintain passivation at 25 ℃ can be determined as a value between 1.37 and 3 M.Furthermore,the corroded surface morphology characterization reveals that equiaxed α phase is more susceptible to corrosion compared to intergranular β3 phase due to a lower content of Nb,Mo,and Zr in the former.     

Effect of Zr on the microstructure, mechanical properties and corrosion resistance of Mg–10Gd–3Y magnesium alloy

The influence of Zr on the microstructure, mechanical properties and corrosion resistance of Mg–10Gd–3Y (wt.%) magnesium alloy was investigated. The grain size of alloys decreased with Zr content from 0% to 0.93% (wt.%). The addition of Zr greatly improved the ultimate tensile strength (UTS) and the elongation (EL), while slightly improved the tensile yield strength (TYS). The UTS and the EL of the alloy containing 0.93% Zr increased by 125.8 MPa and 6.96% compared with base alloy, respectively. The corrosion resistances were found to decrease with Zr content from 0% to 0.42% and then increase from 0.42% to 0.93%. The differences in the sizes and distributions of the Zr-rich particles have significant effects on the corrosion behaviors. The alloy with 0.42% Zr addition revealed the optimum combination of mechanical properties and corrosion resistance.     

Chromate conversion coating on Al-0.2 wt.% Fe alloy

SEM and TEM investigations revealed that the chromate coating developed rapidly over the macroscopic alloy surface. The coating thickness increased over the immersion period employed in this study and was about 50 nm and 200 nm for coatings formed after 30 s and 120 s respectively. The coating is composed of chromium compounds with aluminium compounds probably concentrated at the alloy/coating interface.     

铜碲锂多元合金在3.5%NaCl溶液中腐蚀行为的研究

研究了铜碲锂多元合金中碲对合金耐腐蚀性的影响。经过25℃在 3.5% NaCl溶液中的全浸试验表明铜碲锂多元合金比纯铜具有更好的耐蚀性。利用扫描电镜观察腐蚀试样的表面形貌,发现表面不均匀的覆盖着一层多孔的腐蚀产物。经 X 射线衍射仪分析确定,该腐蚀产物为 Cu2 (OH)3Cl 和 Cu2O 的混合物。     

Enhanced superplasticity of 1 wt.%Ca-AZ80 Mg alloy with ultrafine grains

Ultrafine grained (UFG) 1 % Ca-AZ80 (1CaAZ80) alloy in sheet form could be fabricated by means of high-ratio differential speed rolling (HRDSR) technique. During the rolling, the grain size was markedly reduced from 11.5 to 0.8 μm, and Al₂Ca particles were broken up to smaller ones and dispersed into the matrix. The UFG 1CaAZ80 alloy exhibited a high strength (yield stress = 340 MPa) at room temperature and excellent superplasticity at elevated temperatures. A maximum elongation of ∼ 700% was obtained at 2 × 10^− 4 s^− 1 − 523 K. The currently proposed HRDSR process opens a new opportunity of producing high-performance superplastic magnesium alloy sheets.     

Corrosion behavior of TiN, TiAlN, TiAlSiN thin films deposited on tool steel in the 3.5 wt.% NaCl solution

TiN, TiAlN and TiAlSiN hard coatings were deposited onto AISI H13 tool steel by cathodic arc plasma method. X-ray diffraction (XRD) analysis confirmed that incorporation of Al and Si into TiN led to refinement of microstructure. From the results of potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) test conducted in an aerated 3.5% NaCl solution, the TiAlSiN film showed the best corrosion resistance with the lowest corrosion current density and porosity, the highest protective efficiency and total resistance (pore resistance plus charge transfer resistance).     

Sn-9Zn无铅焊料合金凝固组织及其在时效中的演变

为了考察Sn-9Zn无铅焊料合金凝固组织及其在时效中的演变,制备了不同冷却条件及不同熔体过热度下Sn-9Zn/Cu焊点,并利用扫描电镜和光学显微镜观察了其组织形貌.观察发现:共晶组织随冷却速率提高而显著细化;同时,随炉缓冷凝固时合金形成完全的层片状共晶组织,而空冷和喷水冷却条件下合金除层片状共晶组织外,还形成了杆状富锌相.实验结果还表明,熔体过热度对出炉空冷合金的共晶组织有显著影响,较高的熔体过热度使共晶组织更细密.在空冷合金的时效过程中,杆状富锌相趋于逐渐溶解消失,90℃时效时还发生了共晶组织的显著粗化.     

Influence of texture on corrosion rate of AZ31 Mg alloy in 3.5 wt.% NaCl

In this study, AZ31 Mg alloys with different grain orientation were prepared to investigate the influence of texture on corrosion rate in 3.5 wt.% NaCl. Experimental results showed that texture had significant influence on the corrosion rate of AZ31 in 3.5% NaCl. The corrosion rate of AZ31 dramatically increased with the (0 0 0 1) texture intensity decreased and the (1 0 ?1 0)/(1 1 ?2 0) texture intensity increased. The corrosion rate reached a maximum at about 3 h immersion and subsequently decreased slightly due to the formation of a Mg(OH)₂ corrosion product layer. This study indicates that the corrosion rate of AZ31 Mg alloy in NaCl solution can be modified to some extend by controlling texture.     

Study of Al alloy corrosion in neutral NaCl by the pitting scan technique

The corrosion behavior of commercial Al alloys was studied in neutral 0.6 mol L⁻¹ NaCl by using single-cycle polarization. Qualitative interpretation of pitting scans in both deaerated and naturally aerated NaCl solution, with the aid of corrosion morphology characterization, allowed for inference of the features of localized corrosion as a function of Al substrate nature. Electrochemical characteristic parameters such as pitting (E_pit), repassivation or protection (E_prot) potentials and pit transition potential (E_ptp) were determined. The validity of the difference ΔE = |E_pit − E_prot| as criterion for susceptibility to localized corrosion of aluminium alloys is discussed.     

Effect of annealing on microstructure and mechanical properties of bulk nanocrystalline Fe3Al alloy with 5 wt.% Cu prepared by aluminothermic reaction

Microstructure and mechanical properties of bulk nanocrystalline Fe₃Al based alloy with 5 wt.% Cu prepared by aluminothermic reaction before and after annealed at 873, 1073 and 1273 K for 8 h were investigated. Microstructures of the alloy before and after the annealing consisted of a Fe-Al-Cu matrix, a little Al₂O₃ sphere and Fe₃AlC_x fiber phases. The matrix of the alloy before the annealing was composed a nanocrystalline phase with disordered bcc crystal structure and a little amorphous phase. The amorphous phase disappeared after the annealing and Fe₃Al phase with ordered DO₃ structure appeared in the alloy after annealed at 1073 and 1273 K in the matrix of the alloy. Size of the Fe₃AlC_x fiber phase increased with the annealing temperature. The alloy after the annealing had better plasticity, higher yield strength than that of the alloy before the annealing, and the alloy after annealed at 1273 K had the highest yield strength.     

Effect of torsional oscillations on the stress-strain behavior of Al-5 wt% Mg alloy

The microstructure and mechanical properties of a precipitation hardenable Al-5 wt% Mg alloy subjected to low frequency torsional oscillations and aging treatments are reported in the present work. The stress-strain response was examined at different frequencies (1.53-3.3 Hz) and at constant shear strain amplitude (φ = 5.69 × 10⁻⁴). An excessive in the softening was observed by increasing both frequency of the applied oscillations and deformation temperature. The change in the hardening and softening parameters of stress-strain relations was explained in view of spinodal decomposition in Al-Mg systems. The mean value of activation energy was found to be equal to that quoted for precipitate-dislocation intersection.     

Effect of crystal orientation on corrosion behavior of directionally solidified Mg-4 wt% Zn alloy

Microstructure and crystallographic orientation of directionally solidified Mg-4 wt% Zn alloy were characterized by X-ray computed tomography (XCT) and electron backscatter diffraction (EBSD) in this study. Results reveal that Mg-4 wt% Zn alloy with dendritic microstructure exhibits typical $\left\{0002\right\}$ basal texture along growth direction. Based on this, the effect of grain orientation on corrosion behavior of directionally solidified Mg-4 wt% Zn alloy in 0.9 wt% NaCl solution was investigated. Result shows that $\left\{0002\right\}$ oriented planes have better corrosion resistance than $\left\{11{\displaystyle \overline{2}}0\right\}$ and $\left\{10{\displaystyle \overline{1}}0\right\}$ ones, which is attributed to a synergistic effect of surface energy, atomic packing density and the stability of oxidation film.     

Effect of Mn on damping capacities, mechanical properties, and corrosion behaviour of high damping Mg–3 wt.%Ni based alloy

The effect of Mn on the damping capacities, mechanical properties, and corrosion behaviour of high damping Mg–3 wt.%Ni based alloys has been studied. The damping vs. strain amplitude spectrum of the studied alloys could be divided into three parts. The strain amplitude weakly dependent part appears again when the microplastic strain occurs at high strain amplitude. The mechanical properties of as-cast Mg–3 wt.%Ni alloy could be improved by the addition of Mn, which is due to the refinement of α-Mg dendrites and solid solution strengthening by Mn. In addition, the corrosion resistance of the alloys could also be improved remarkably by the addition of Mn.     

Effect of hydrogen charging on microstructural evolution and corrosion behavior of Ti-4Al-2V-1Mo-1Fe alloy

The effect of hydro gen charging on microstructural evolution and corrosion behavior of a Ti-4Al-2V-1Mo-1Fe alloy in a 3.5 wt.% NaCl solution was investigated.The results showed that the hydrogen charging induced the formation and growth of γ-TiH and δ-TiH₂ phases,leading to the initiation and propagation of hydrogen-induced cracks.It was also found that hydrogen charging can change the passivity of this alloy and increase its pitting corrosion susceptibility.The main reason for these was attributed to the fo rmation of hydrides in α phase in the Ti-4Al-2V-1Mo-1Fe alloy,leading to the preferential dissolution of the α phase and thus the deterioration in the protective ability of passive film.     

Viscoplastic behavior of a FeCrAl alloy for high temperature steam electrolysis (HTSE) sealing applications between 700 °C and 900 °C

High temperature steam electrolysis (HTSE) is one of the most promising technologies for the industrial production of hydrogen. However one of the remaining problems lies in sealing at high temperature. The reference solution is based on glass seals which presents several drawbacks. That explains why metallic seals are under development. The expected seal will be submitted to creep under low stresses between 700 °C and 900 °C, possibly involving complex loading and thermal history. The candidate material investigated in this work is a FeCrAl (OC404, Sandvik) supplied as a 0.3 mm thick sheet. The ability of this material to develop a protective layer of alumina was studied first, as well as grain size growth during thermal ageing. Creep and tensile tests were performed between 700 °C and 900 °C to determine its mechanical properties. This database was used to propose and identify an elasto-viscoplastic behavior for the material. Creep was described by the Sellars-Tegart law. This law was then used to simulate and predict creep indentation tests performed in the same range of temperatures.