Corrosion fatigue of extruded magnesium alloys

Corrosion fatigue tests were carried out on extruded AZ31 (3% Al, 1% Zn, 0.3% Mn, Mg—the rest), AM50 (5% Al, 0.4% Mn, Mg—the rest) and ZK60 (5% Zn, 0.5% Zr, Mg—the rest) Mg alloys in air, NaCl-based and borate solutions. N_sol/N_air ratios (the relative fatigue life) were used for the analysis of the corrosion fatigue behavior of Mg alloys in various environments, where N_sol and N_air are the numbers of cycles to failure in the solution and in air, respectively. Extruded ZK60 alloy reveals very high fatigue and corrosion fatigue properties in comparison with other alloys. However, it has the lowest relative fatigue life (N_sol/N_air 10⁻³–10⁻²) or the highest sensitivity to the action of NaCl-based solutions in comparison with that of AM50 and AZ31 alloys (N_sol/N_air 10⁻²–10⁻¹). Under the same stress, the corrosion fatigue life of extruded alloys is significantly longer than that of die-cast alloys (N_sol for extruded AM50 in NaCl is two to three times longer than that of die-cast AM50).     

Corrosion behaviour of some vapour deposited magnesium alloys

Abstract

Binary magnesium alloys containing chromium, manganese, or titanium were made using a physical vapour deposition technique. The corrosion resistance of the alloys was assessed in aqueous chloride solutions using total immersion tests in quiescent 600 mmol L^?1 NaCI solutions. Alloying with manganese or titanium was found to lower the corrosion rate of magnesium over most of the compositional ranges of interest, whereas addition of chromium had a detrimental effect on the corrosion resistance of magnesium. The lowest corrosion rate was recorded for a Mg–Ti alloy where the value obtained was about 80 times lower than that found for vapour deposited pure magnesium. Open circuit corrosion potential measurements conducted in 600 mmol L^?1 NaCl solution showed that additions of chromium, titanium, and manganese also produced deposits which were significantly more noble than pure magnesium, suggesting that these alloys would be less susceptible to galvanic corrosion.

MST/3064     

Corrosion evaluation of Au-Cu-Pd ternary alloys

The corrosion resistivity of single-phase Au-Cu-11 at% Pd alloys was evaluated by using a parameterQ which represented the total amount of anodic reaction in a potentiostatic polarization test. The result was compared with those for binary Au-Cu, ternary Au-Cu-11 at % Ag and some commercial alloys. The validity of usingQ as a corrosion parameter was confirmed by the good agreement between the analysed and calculated values of copper ion dissolved into the test solution. By replacing a part of the copper in Au-Cu alloys with palladium the corrosion resistivity can be greatly improved, but silver has no such significant effect. The value ofQ decreased by both treatments of homogenization and grain refinement of the alloy. One of the advantages of the alloy having a single-phase structure is that inhomogeneity in the distribution of the constituents is small even in the as-cast state, which results in a small galvanic effect.     

Micro-arc oxidation of magnesium alloys: A review

Magnesium(Mg) and its alloys present great potential to be extensively applied in different applications.However, the relatively poor resistance to corrosion and wear significantly restricts their applications in practice. As one of strategies of surface treatment, micro-arc oxidation(MAO) process attracts a lot of attention, since it does not use neither expensive equipment, nor complicated manipulation. This review systematically discusses MAO mechanism and some typical models, which still nee...     

Layered double hydroxide coatings on magnesium alloys: A review

Layered double hydroxides (LDHs) as a class of anionic clays have extensive applications due to their unique structures. Nowadays, the emphasis is laid on the development of LDH coatings for corrosion resistance and medical applications. Thus, this review highlights synthetic methods of LDH coatings and LDH-based composite coatings on magnesium alloys. Special attention is focused on self-healing, biocompatible and self-cleaning LDH-based composite coatings on magnesium alloys.     

医用Mg-Zn-Ca-Mn合金在PBS模拟体液中的腐蚀行为

利用真空感应熔炼,采用金属模浇铸制备了Mg(100-x-y-z)-Znx-Cay-Mnz四元合金。使用光学显微镜、X射线衍射仪、扫描电镜及能谱仪对合金进行分析和表征。探讨了合金在PBS模拟体液中的腐蚀行为。结果表明,Ca、Zn及Mn原子的复合加入可显著细化合金的铸态显微组织;镁合金的腐蚀发生于晶粒内部,至晶界处终止;当加入2.0%的Zn和0.5%的Ca时,铸态合金的抗腐蚀性能最佳(平均腐蚀速率为0.77mm/a);当Zn、Ca含量均大于1%时,固溶时效态合金的腐蚀速率下降为铸态的1/2～1/4,表现出优异的耐蚀性;固溶时效处理可有效减少Mg2Ca相的体积分数,改善其分布,提高合金的耐蚀性能。     

Cytocompatibility evaluation of different biodegradable magnesium alloys with human mesenchymal stem cells

In the last few years, the use of biodegradable magnesium (Mg) alloys has evoked great interest in the orthopedic field due to great advantages over long-term implant materials associated with various side effects like allergy and sensitization and consequent implant removal surgeries. However, degradation of these Mg alloys results in ion release, which may cause severe cytotoxicity and undesirable complications after implantation. In this study, we investigated the cytological effects of various Mg alloys on cells that play an important role in bone repair. Eight different magnesium alloys containing varying amounts of Al, Zn, Nd and Y were either incubated directly or indirectly with the osteosarcoma cell line Saos-2 or with uninduced and osteogenically-induced human mesenchymal stem cells (MSCs) isolated from bone marrow specimens obtained from the femoral shaft of patients undergoing total hip replacement. Cell viability, cell attachment and the release of ions were investigated at different time points in vitro. During direct or indirect incubation different cytotoxic effects of the Mg alloys on Saos-2 cells and osteogenically-induced or uninduced MSCs were observed. Furthermore, the concentration of degradation products released from the Mg alloys differed. Overall, Mg alloys MgNd2, MgY4, MgAl9Zn1 and MgY4Nd2 exhibit good cytocompatibility. In conclusion, this study reveals the necessity of cytocompatibility evaluation of new biodegradable magnesium alloys with cells that will get in direct contact to the implant material. Furthermore, the use of standardized experimental in vitro assays is necessary in order to reliably and effectively characterize new Mg alloys before performing in vivo experiments.     

Superplasticity of fine-grained magnesium alloys for biomedical applications: A comprehensive review

The superplastic behavior of medical magnesium alloys is reviewed in this overview article. Firstly, the basics of superplasticity and superplastic forming via grain boundary sliding (GBS) as the main deformation mechanism are discussed. Subsequently, the biomedical Mg alloys and their properties are tabulated. Afterwards, the superplasticity of biocompatible Mg-Al, Mg-Zn, Mg-Li, and Mg-RE (rare earth) alloys is critically discussed, where the influence of grain size, hot deformation temperature, and strain rate on the tensile ductility (elongation to failure) is assessed. Moreover, the thermomechanical processing routes (e.g. by dynamic recrystallization (DRX)) and severe plastic deformation (SPD) methods for grain refinement and superplasticity in each alloying system are introduced. The importance of thermal stability (thermostability) of the microstructure against the grain coarsening (grain growth) is emphasized, where the addition of alloying elements for the formation of thermally stable pinning particles and segregation of solutes at grain boundaries are found to be major controlling factors. It is revealed that superplasticity at very high temperatures can be achieved in the presence of stable rare-earth intermetallics. On the other hand, the high-strain-rate superplasticity and low-temperature superplasticity in Mg alloys with great potential for industrial applications are summarized. In this regard, it is shown that the ultrafine-grained (UFG) duplex Mg-Li alloys might show remarkable superplasticity at low temperatures. Finally, the future prospects and distinct research suggestions are summarized. Accordingly, this paper presents the opportunities that superplastic Mg alloys can offer for the biomedical industries.     

Corrosion of gallium alloys in vivo

The aim of this work was to study the corrosion of gallium alloys in vivo. Three gallium alloys were tested: GF alloy, Galloy and an experimental GaIn alloy. An amalgam was applied as a control. After ageing for a minimum of two weeks, one disc of each of these alloys was mounted with the polished side up in the buccal surfaces of 17 acrylic dentures. Eight sets of the specimens were retrieved after exposure to the oral cavity for 2–4 months, and another seven were retrieved after 6–9 months. Corrosion of the polished cross-sections of the specimens was studied using scanning electron microscopy (SEM). Only the CuGa2 phase was found to corrode substantially in all three of the alloys investigated, leaving behind holes up to 20 m deep. This is consistent with the corrosion reported after immersion tests in a solution of 0.1 mol lactic acid and 0.1 mol NaCl for 7 days. Such in vitro tests are also reported to cause distinct corrosion of the Sn phase in the gallium alloys. However, a salient feature of the corrosion in vivo was the lack of detectable dissolution of this phase. Thus, for gallium alloys, the accelerated in vitro immersion method produced results which did not agree with clinical observations. Large variations in the corrosion of the CuGa2 were observed from patient to patient. The amount of corrosion on the Galloy specimens appeared to be less and on a finer scale than on specimens of the two other alloys. The depth of corrosion was thus shallower than for this alloy. This finding indicates that there is room for further improvement of the corrosion resistance by modifying the microstructures. Less overall corrosion was found for the amalgam control than for the gallium alloys.     

Improvement of formability and mechanical properties of magnesium alloys via pre-twinning: A review

Twinning can generate the change of texture and a large of twin boundaries, which can greatly influence the mechanical properties of magnesium alloys. Thus, pre-twinning can be considered to be a simple and feasible method to improve the mechanical properties of magnesium alloys. Recently, some studies have confirmed that pre-twinning can be an effective way to enhance the strength, formability and mechanical anisotropy of magnesium alloys. Based on these results, some aspects of the present research on the improvement of mechanical properties via pre-twinning are reviewed. The relevant mechanisms have been summarized. Finally, for this research field, a few critical scientific problems are also proposed.     

Corrosion fatigue behavior of extruded AZ80, AZ61, and AM60 magnesium alloys in distilled water

Rotary bending fatigue tests were conducted in laboratory air and distilled water using three extruded magnesium (Mg) alloys AZ80, AZ61, and AM60 with different chemical compositions. In laboratory air, the fatigue strengths at high stress levels were similar in all alloys because cracks initiated at Al-Mg intermetallic compounds, whereas AZ80 with the largest Al content exhibited the highest fatigue strength at low stress levels, which was attributed to the crack initiation due to cyclic slip deformation in the matrix microstructure. In distilled water, fatigue strengths were considerably decreased due to the formation of corrosion pits in all alloys, and the difference of fatigue strength at low stress levels among the alloys disappeared, indicating that the addition of Al that improved the fatigue strength in laboratory air was detrimental to corrosion fatigue. __________ Translated from Problemy Prochnosti, No. 1, pp. 141–145, January–February, 2008.     

Structural durability of magnesium alloys and components

The fatigue behaviour of the magnesium die cast alloys AZ91, AE42 and AM50 was investigated at constant amplitude and in variable amplitude tests. The ambient conditions of these tests varied between laboratory air at room temperature, at 125 °C and a permanent influence of NaCl‐solution at room temperature. More than 40 test series were analysed in a generalized way to determine standardized slopes of S‐N curves and mean stress sensitivity. The behaviour of the three alloys was investigated also in strain‐controlled cyclic tests at normal and elevated temperature. Based on this substantial data set several variants of methods following both the nominal‐stress concept and the local‐strain approach were applied to determine guidelines to improve the reliability of lifetime estimation of components made of magnesium. The corrosion fatigue behaviour of these magnesium alloys was extensively investigated under rotating bending to clarify the damaging influence of the corrosive load component. Under simultaneous action of corrosion and cyclic mechanical loading several influencing factors have to be considered which attain special importance during the testing of magnesium alloys.     

Effect of silicon on damping capacities of pure magnesium and magnesium alloys

A new idea of using a stiffer metallic compound Mg₂Si to enhance the damping capacities of pure magnesium and its alloys is successfully attempted. The present paper focuses on the relation between damping capacities and the addition amount of Si. The results show that damping capacities increase with increasing amount of Si. Particular emphasis is placed on the increasing dislocation density around matrix-particulate interface and the refinement of grain size promoted by big growth restriction factor of Si.     

Corrosion behavior of metals and alloys in marine-industrial environment

Abstract

This work deals with atmospheric corrosion to assess the degrading effects of air pollutants on ferrous and non-ferrous metals and alloys, which are mostly used as engineering materials. An exposure study was conducted in the Tuticorin port area located on the east coast of South India, in the Gulf of Mannar with Sri Lanka to the southeast. Common engineering materials, namely mild steel, galvanized iron, Zn, Al, Cu and Cu–Zn alloys (Cu–27Zn, Cu–30Zn and Cu–37Zn), were used in the investigation. The site was chosen where the metals are exposed to marine and industrial atmospheres. Seasonal 1 to 12 month corrosion losses of these metals and alloys were determined by a weight loss method. The weight losses showed strong corrosion of mild steel, galvanized iron, Cu and Zn and minor effect on Al and Cu–Zn alloys. Linear regression analysis was conducted to study the mechanism of corrosion. The composition of corrosion products formed on the metal surfaces was identified by x-ray diffraction and Fourier transform infrared spectroscopy.     

Corrosion behavior of metals and alloys in marine-industrial environment

This work deals with atmospheric corrosion to assess the degrading effects of air pollutants on ferrous and non-ferrous metals and alloys, which are mostly used as engineering materials. An exposure study was conducted in the Tuticorin port area located on the east coast of South India, in the Gulf of Mannar with Sri Lanka to the southeast. Common engineering materials, namely mild steel, galvanized iron, Zn, Al, Cu and Cu–Zn alloys (Cu–27Zn, Cu–30Zn and Cu–37Zn), were used in the investigation. The site was chosen where the metals are exposed to marine and industrial atmospheres. Seasonal 1 to 12 month corrosion losses of these metals and alloys were determined by a weight loss method. The weight losses showed strong corrosion of mild steel, galvanized iron, Cu and Zn and minor effect on Al and Cu–Zn alloys. Linear regression analysis was conducted to study the mechanism of corrosion. The composition of corrosion products formed on the metal surfaces was identified by x-ray diffraction and Fourier transform infrared spectroscopy.     

Thermal and electrical conductivity of binary magnesium alloys

Thermal conductivity is a key parameter for thermal design and management of the electronic components in their passive cooling processes. In this work, thermal and electrical conductivities of six groups of binary Mg alloys (Mg–Al, Mg–Zn, Mg–Sn, Mg–Zr, Mg–Mn, and Mg–Ca) in as-cast, as-solution, and annealed states were measured and the corresponding microstructures were observed. In both as-cast and as-solution states, thermal/electrical conductivities of the six groups of Mg alloys decreased with composition. Effects of solution treatment and annealing on thermal/electrical conductivities of the as-cast samples were also investigated and discussed. Moreover, the specific thermal/electrical resistivity (thermal/electrical resistivity increment of the alloy derived from one atom addition) of the solute elements for Mg alloys was drawn as follows, Zn < Al < Ca < Sn < Mn < Zr. Atomic volume difference of the solute elements with Mg atom (ΔV/V _Mg), valency, and configuration of extra-nuclear electron of the solute were believed as the main reasons for the differences.