Effect of corrosion product films on the in vitro degradation behavior of Mg-3%Al-1%Zn (in wt%) alloy in Hank’s solution

Through investigating the corrosion behavior of an as-extruded Mg-3wt%Al-1wt%Zn (AZ31) alloy in a simulated physiological fluid of Hank’s solution, it demonstrates that the corrosion process was dependent on the immersion time. Further analyses revealed that the highest corrosion resistance could be obtained at 24?h due to the formation of a compact layer of corrosion products on the sample surface. With increasing the immersion time to up to 48?h, the thickness of surface films increased gradually but obvious de-bonding of such film from the substrate could take place, resulting in a certain resilience of the overall corrosion resistance.     

In vitro corrosion behaviour of Mg alloys in a phosphate buffered solution for bone implant application

The corrosion behaviour of Mg–Mn and Mg–Mn–Zn magnesium alloy in a phosphate buffered simulated body fluid (SBF) has been investigated by electrochemical testing and weight loss experiment for bone implant application. Long passivation stage and noble breakdown potential in the polarization curves indicated that a passive layer could be rapidly formed on the surface of magnesium alloy in the phosphate buffered SBF, which in turn can protect magnesium from fast corrosion. Surfaces of the immersed magnesium alloy were characterized by SEM, EDS, SAXS and XPS. Results have shown that Mg–Mn and Mg–Mn–Zn alloy were covered completely by an amorphous Mg-containing phosphate reaction layer after 24 h immersion. The corrosion behaviour of magnesium alloys can be described by the dissolving of magnesium through the reaction between magnesium and solution and the precipitating of Mg-containing phosphate on the magnesium surface. Weight loss rate and weight gain rate results have indicated that magnesium alloys were corroded seriously at the first 48 h while Mg-containing phosphate precipitated fast on the surface of magnesium alloy. After 48–96 h immersion, the corrosion reaction and the precipitation reaction reach a stable stage, displaying that the phosphate layer on magnesium surface, especially Zn-containing phosphate layer could provide effective protection for magnesium alloy.     

Influence of cerium content on the corrosion behavior of Al-Co-Ce amorphous alloys in 0.6 M NaCl solution

The effect of cerium content on the corrosion behavior of Al-Co-Ce amorphous alloys in 0.6 M NaCl solution was investigated by cyclic polarization, Mott-Schottky and X-ray photoelectron spectroscopy techniques. Results indicated that the open circuit potential of Al-Co-Ce amorphous alloys displayed a decreased tendency with the increase in Ce content, and the amorphous alloy with 4 at.% Ce presented both the lowest passive current density and donor density indicating the best corrosion resistance, while adding excess Ce led to the reduced corrosion resistance of Al-Co-Ce alloys. Furthermore, it was found that a low Ce content is beneficial to the formation of a more protective passive film on Al-Co-Ce amorphous alloys, and the corrosion inhibition reactions of Al-Co-Ce alloys in 0.6 M NaCl solution were changed with the increase in Ce content and the detailed reasons were discussed.     

Influence of Si,Ca and Ag addition on corrosion behaviour of new wrought Mg–Zn alloys

Abstract

The development of new wrought magnesium alloys for automotive industry has increased in recent years owing to their high potential as structural materials for low density and high strength/weight ratio demands. However, the poor mechanical properties and low corrosion resistance of the magnesium alloys have led to searching a new kind of magnesium alloys for better strength, ductility and high corrosion resistance. The main objective of the present research is to investigate the mechanical properties and the corrosion behaviour of new magnesium alloys, Mg–Zn–Ag (ZQ) and Mg–Zn–Si–Ca (ZS) alloys. The ZQ6X and ZS6X–YCa alloys were prepared by using hot extrusion method. Hardness AC and DC polarisation tests were carried out on the extruded rods, which contain different amounts of silver or silicon and calcium. The potential difference in air between different phases and the matrix was examined using scanning Kelvin probe force microscopy. The microstructure was examined using optical and electron microscopy (TEM and SEM), X-ray analysis and EDS. The results showed that the silver addition improved the mechanical properties but decreased the corrosion resistance. The addition of silicon and calcium also affected both mechanical properties and corrosion behaviour. These results can be explained by the effects of alloying elements on microstructure of Mg–Zn alloys such as grain size and precipitates caused by the change in precipitation and recrystallisation behaviour.     

Influence of Alternative Magnetic Field on the Diffusion of Al and Mg

The influence of an alternative magnetic field on the diffusion of Al and Mg in AI-Mg diffusion couple is studied. The diffusion zone is composed of two intermediate phases, namelyβ and γ phase. Thickness of each intermediate phase is examined. The results show that the alternative magnetic field increases the thicknesses of βand γ phase zone and the layer growth ofβ and γphase obeys the parabolic rate law. The growth rate of the β and γ phase are increased with the application of the alternative magnetic field. This change is manifested through a change in the frequency factor k0 and not through a change in the activation energy Q. The frequency factor k0 for intermediate phase growth with an alternative magnetic field is 39.95 cm2/s for 7 phase and 2.84×10-4 cm2/s for β phase compared with those without the magnetic field is 22.4 cm2/s for 7 phase and 1.53×10-4 cm2/s for β phase.     

Influence of Ringer’s solution on creep resistance of hydroxyapatite reinforced polyethylene composites

In vitro creep studies of polyethylene, both unfilled and filled with hydroxyapatite at 0.20 and 0.40 volume fraction, have been performed. The samples were immersed in Ringer's solution at 37 degrees C for 1, 7, 30, 90 and 150 days prior to isochronous and creep tests in the same condition. The creep properties of unfilled polyethylene is unaffected by the immersion, but the isochronous modulus and the creep resistance of filled polyethylene were reduced. The effect increased with increasing volume fraction and time of immersion. This reduction is related to the penetration of the solution into the material, softening the interface.     

Influence of temperature on the pitting corrosion behavior of AISI 316L in chloride–CO2 (sat.) solutions

The paper discusses the pitting corrosion behavior of AISI (American iron and steel institute) 316L stainless steel in aerated chloride solutions (0.1–2 M NaCl) at 25, 50 and 80 °C using potentiodynamic polarization technique. A comparison is made with CO₂-saturated chloride solutions. The results have revealed that pitting potential decreased in a logarithmic relationship with the chloride concentration, and decreased linearly with temperature. The influence of CO₂ on the chloride pitting of AISI 316L stainless steel is quite complex and found to be dependent on chloride concentration and test temperature. At 25 °C the presence of CO₂ appears to have insignificant effect on E_p irrespective of chloride concentration. As the temperature is raised to 50 or 80 °C the additions of CO₂ has caused marked negative shifts in pitting potential. The detrimental effect of CO₂ increases with NaCl concentration and temperature. The results indicate that pitting potential (E_p) is influenced by a synergy between chloride, CO₂ and temperature, and that this synergy depends on the chloride concentration and test temperature.     

Mössbauer spectroscopy study on the corrosion resistance of plasma nitrided ASTM F138 stainless steel in chloride solution

Plasma nitriding of ASTM F138 stainless steel samples has been carried out using dc glow discharge under 80% H₂–20% N₂ gas mixture, at 673 K, and 2, 4, and 7 h time intervals, in order to investigate the influence of treatment time on the microstructure and the corrosion resistance properties. The samples were characterized by scanning electron microscopy, glancing angle X-ray diffraction and conversion electron Mössbauer spectroscopy, besides electrochemical tests in NaCl aerated solution. A modified layer of about 6 μm was observed for all the nitrided samples, independent of nitriding time. The X-ray diffraction analysis shows broad γ_N phase peaks, signifying a great degree of nitrogen supersaturation. Besides γ_N, the Mössbauer spectroscopy results indicated the occurrence of γ′ and ε phases, as well as some other less important phases. Corrosion measurements demonstrate that the plasma nitriding time affects the corrosion resistance and the best performance is reached at 4 h treatment. It seems that the ε/γ′ fraction ratio plays an important role on the resistance corrosion. Additionally, the Mössbauer spectroscopy was decisive in this study, since it was able to identify and quantify the iron phases that influence the corrosion resistance of plasma nitrided ASTM F138 samples.     

Influence of grain-boundary pre-precipitation and corrosion characteristics of inter-granular phases on corrosion behaviors of an Al–Zn–Mg–Cu alloy

In this paper the influence of high-temperature pre-precipitation treatment on corrosion behaviors of 7055 aluminum alloy is investigated. High-temperature pre-precipitation treatment enhances the discontinuing distribution of the coarse precipitates along the grain boundary, and increases the Cu content of grain-boundary precipitates, which obviously improves stress corrosion resistance, suppresses the serve fracture of sub-grain boundary under the stress corrosion and reduces inter-granular corrosion (IGC) susceptibility with the same strength and ductility. The electrochemical corrosion results of inter-granular phases indicate that the Cu-rich, discrete and coarse grain-boundary precipitates and the decreasing potential difference among inter-granular phases in the grain boundary are responsible for the enhancement of corrosion resistance of 7055 alloy.     

Preparation of superhydrophobic Li–Al-Ala LDH/SA film with enhanced corrosion resistance and mechanical stability on AZ91D Mg alloy

Journal of Materials Science - Layered double hydroxide (LDH) films have attracted extensive attention in Mg alloy anti-corrosion due to their unique physical barrier function and ion exchange...     

Influence of retrogression and re-aging treatment on corrosion behaviour of an Al–Zn–Mg–Cu alloy

Influence of retrogression and re-aging treatment on the microstructure, strength, exfoliation corrosion, inter-granular corrosion and stress corrosion cracking of an Al–Zn–Mg–Cu alloy has been investigated by means of optical microscope (OM), transmission electron microscope (TEM) and electrochemical impedance spectroscopy (EIS). The results show that retrogression and re-aging treatment can increase the size and the distribution discontinuity of the grain boundary precipitates, and lead to the increase of the corrosion resistance without the loss of strength and ductility. In addition, the analysis of electrochemical impedance spectroscopy shows that retrogression and re-aging treatment can enhance the resistance to exfoliation corrosion.     

Influence of heat treatment on microstructure and passivity of Cu–30Zn–1Sn alloy in buffer solution containing chloride ions

Tin as an alloying element is of great interest in brasses for dezincification impediment. In this paper, Cu–30Zn–1Sn alloy was submitted to three different heat treatments, viz. A (heating up to 800 °C for 20 h, held at 200 °C for 20 h in salt bath and air cooled), B (heating up to 800 °C for 20 h and water quenched) and C (heating up to 600 °C for 20 h and water quenched). The influence of heat treatment on microstructure was evaluated by OM and SEM–EDS analysis. The corrosion resistance in buffer solution (pH 9), H₃BO₃/Na₂B₄O₇ ·10H₂O, with various concentrations of chloride ions was evaluated by potentiodynamic polarization curves and compared with multi-component Pourbaix diagrams. A correlation between the heat treatment, microstructure and passivity of the heat treated samples was observed. The results indicated that all heat treatment procedures led to formation of α, and γ-Sn-rich phases as microstructure constituents with a small fraction of β′ phase in A. Sn-rich phase appears in grain boundaries and its morphology was slightly changed due to heat treatment. Beneficial influence of low concentration chloride ions on passivity was associated with the formation of copper oxides/hydroxide and chloride complexes. Deterioration was observed at concentrations higher than 0·05 M NaCl due to accelerated dissolution of copper by formation of CuCl₂^-_{2}^{-}. As a result of dezincification process, preferential corrosion attack and copper redeposition on α phase (matrix) were observed. However, Sn-rich (γ₁) phase in grain boundaries was not attacked due to SnO₂ formation. In buffer solution, the higher passivity current density in A was related to the presence of small amount of β′ phase. On the other hand, in 1 M NaCl, lower critical current density for passivation in B and A (about two times lower than C) was attributed to the grain size effect.     

Influence of the combined addition of Y and Nd on the microstructure and mechanical properties of Mg–Li alloy

Y and Nd are simultaneously added into Mg–5Li–3Al–2Zn alloy. It is found that there exist the phases of α-Mg, AlLi, Al₁₁Nd₃ and Al₂Y in the alloys. When the contents of Y and Nd are 1.2% and 0.8%, respectively, the grain is the finest with an average size of 30 μm, and the tensile strength of the alloy reaches 231 MPa, the elongation reaches 16%. When the ratio of Y to Nd is 1.2:0.8, there is a synergistic strengthening effect.     

Effects of Zn on microstructure,mechanical properties and corrosion behavior of Mg–Zn alloys

In this study, binary Mg–Zn alloys were fabricated with high-purity raw materials and by a clean melting process. The effects of Zn on the microstructure, mechanical property and corrosion behavior of the as-cast Mg–Zn alloys were studied using direct observations, tensile testing, immersion tests and electrochemical evaluations. Results indicate that the microstructure of Mg–Zn alloys typically consists of primary α-Mg matrix and MgZn intermetallic phase mainly distributed along grain boundary. The improvement in mechanical performances for Mg–Zn alloys with Zn content until 5% of weight is corresponding to fine grain strengthening, solid solution strengthening and second phase strengthening. Polarization test has shown the beneficial effect of Zn element on the formation of a protective film on the surface of alloys. Mg–5Zn alloy exhibits the best anti-corrosion property. However, further increase of Zn content until 7% of weight deteriorates the corrosion rate which is driven by galvanic couple effect.     

Influence of high velocity oxygen-fuel spraying parameters on the wear resistance of Al–SiC composite coatings deposited on ZE41A magnesium alloy

High velocity oxygen-fuel (HVOF) has been used as fabrication technique to deposit aluminium coatings reinforced with silicon carbide particles on Mg–Zn substrates. The aim of the investigation is to improve the tribological performance of the ZE41A magnesium alloy. The parameters of the thermal spraying system have been optimized in order to maximize the SiC particles incorporation in the aluminium matrix of the coating and to minimize the mechanical deterioration of the light alloy substrate. Pin-on-disc tests were developed to characterize the tribological behavior of the different specimens. Composite coatings with thicknesses of 120 μm, reinforced with ∼10 wt% and with high adhesion to the substrate were achieved. The wear resistance of the substrates was increased and the wear rate decreased in two orders of magnitude respect to that of the bare Mg-alloy after the optimization of the spraying parameters.     

The Influence of Thermal Expansion and Mass Loss on the Young’s Modulus of Ceramics During Firing

During the heating stage of the firing of a ceramic material, the mass \(m\) , length \(l\) , and diameter \(d\) of the sample alter their values depending on the temperature \(t\) . Young’s modulus \(E(f,m,l,d)\) measured by a sonic resonance method is also a function of the resonance frequency \(f\) . Therefore, three thermal analyses (TGA, TDA, modulated force TMA) must be performed to obtain correct values of Young’s modulus. The calculation of Young’s modulus can be simplified if TGA and/or TDA are omitted. This necessarily leads to partly incorrect results. If TGA is not performed, we have \(E[f(t),m_0 ,l(t),d(t)]\) and the relative difference \((\{E[f(t),m(t),l(t),d(t)]-E[f(t),m_0 ,l(t),d(t)]\}/E[f(t),m(t),l(t),d(t)])\) reaches 7 % for \(t> 650\,^\circ \text{ C}\) and less than 2 % for \(t< 500\,^\circ \text{ C}\) . If TDA is not performed, we have \(E[f(t),m(t),l_0 ,d_0 ]\) and the relative difference ( \(\{E[f(t),m(t),l(t),d(t)]-E[f(t),m(t),l_0 ,d_0 ]\}/E[f(t),m(t),l(t),d(t)])\) is less than 0.6 % for \(t < 1000\,^\circ \text{ C}\) . For the simplest case, we have \(E[f(t),m_0 ,l_0 ,d_0 ]\) and the relative difference ( \(\{E[f(t),m(t),l(t),d(t)]-E[f(t),m_0 ,l_0 ,d_0 ]\}/E[f(t),m(t),l(t),d(t)])\) is 7.5 % for \(t > 600\,^\circ \text{ C}\) and less than 2 % for \(t<500\,^\circ \text{ C}\) .     

Effect of additions of Mn,Ce, Nd,and Si on rate of dissolution of splat quenched Mg–Al and Mg–Zn alloys in 3%NaCl solution

Abstract

Weight loss resulting from immersion in 3%NaCl solution buffered with Mg(OH)₂ has been determined for Mg alloy splats containing different levels of alloying with Zn or Al with and without ternary additions of Mn, Ce, Nd, and Si. The results show that additions of Zn increase the rate of dissolution, whereas an addition of 15 wt-%Al significantly reduces the dissolution rate. Ternary additions of Mn significantly reduce the dissolution rate of both Mg–Zn and Mg–Al alloys, whereas Ce and Nd reduce the dissolution rate of Mg–Al alloys. Additions of Si to Mg–Zn slightly increase the dissolution rate. These results are discussed in the context of other reported observations on the corrosion behaviour of rapidly solidified Mg alloys.

MST/I098