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The Shuttleworth equation for the solid surface stress ϒ (surface area A) uses the strain derivative of the total surface energy AF. The formal disclosure of this derivative leads to a nonsensical approach if applied to a 3D body of volume V with free energy density FV.

The review presents brief theoretical foundations of the mechanochemical and chemomechanical surface effects (MCE and CME) associated with corrosion-mechanical destruction of metals, considers the results of various scientific publications that studied the mechanochemical behavior of steels in near-neutral pH media, and analyzes the application of the results of such studies with the purpose of their practical use in the stress corrosion cracking (SCC) prevention. The article attempts to summarize the results of modern experimental studies and numerical modeling of mechanochemical and chemomechanical processes occurring on the surface of pipe steels and at the tip of the crack under the simultaneous effects of stresses/strains and corrosion media. The influence of these processes on the mechanism and kinetics of corrosion cracking of pipe steels in near-neutral aqueous solutions is discussed. The criteria for the quantitative assessment of the influence of MCE and CME on the SCC of pipeline steels are considered. The analysis of research methods for the study of MCE and CME, was carried out with the aim of further developing a unified methodological approach to assessment and quantification in predicting SCC in neutral media.

There are serious problems with the formability of alloys which are relatively hard and brittle below ambient temperatures, e.g., in cold extrusion and drawing processes. It is known that electrochemical surface treatment can decrease residual stresses and hardness of the surface layer as a result of the chemomechanical effect (CME), and also improve the plastic deformation ability, e.g., deep drawing of high-strength alloys. Plastic deformation ability of materials can be characterized by hardness measurements. The present study shows some possibilities to improve the surface ductility of carbon steels and FeSi6.5 steel under anodic polarization depending on the current density, composition and pH of acids and chloride electrolytes. The relative Vickers hardness (RVH) amounting to a squared ratio of the penetration depth of a cone indenter in air as compared to that in a solution (hair/hsol)2 was found as a function of the current density and the electrolyte composition. A decrease in hardness of the surface layer as a result of anodic electrochemical polarization was found for different steels.

Stability loss of a thin-walled spherical shell, subjected to external pressure and internal corrosion, is studied. The critical time of stability loss of the shell is found by combining the upper critical load value for static stability loss of the shell without corrosion, and the corrosion rate law. Numerical results, obtained for carbon steel shells with different wall thickness at different temperatures and corrosion activation energy values, indicate that increase in the safety coefficient for stability yields reduction of the relative durability. Temperature growth leads to corrosion rate increase and yields reduction of the vessel “life-time”. The value of activation energy of corrosion has great impact on the vessel critical time t ∗ − the less is this parameter the less is the critical time.

In the previous paper (Gutman, JOSSEC 18:3217–3237, 2014), we have shown that the main problem in capillarity and electrocapillarity of solid surfaces is the lack of clarity in determining the surface stress and basic equations. Now, we continue the survey of efforts to solve this problem and show origins of erroneous results, accenting some important items: comparative analysis of Gibbs and Guggenheim approaches in surface thermodynamics (a geometrical dividing surface and finite-thickness surface layer, respectively), transformation of fundamental equations on per-unit-area basis to obtain Gibbs adsorption equation for finite-thickness surface layer, different attempts to derive the thermodynamic definition of “surface stress” in frames of Gibbs’ theory (including Shuttleworth’s approach), atomistic calculations of surface stress, surface stress in rational continuum mechanics, “modifications” of Gibbs–Duhem relations made for solid interface, and Maxwell relations in capillarity and electrocapillarity of solid interface. It is shown that the erroneous Shuttleworth’s approach is present in an explicit or implicit form in all efforts to introduce the surface stress in frames of Gibbsian theory (although Gibbs did not introduce surface stress). Therefore, “modernizations” or “generalizations” of the Gibbs–Duhem relation, the Gibbs adsorption equation, and the Lippmann equation to adopt them for a solid surface are unnatural and not necessary. Therefore, we recommend withdrawing the Shuttleworth equation and its consequences from circulation, including the IUPAC Recommendations.

• “Simple thermodynamic derivation of the electrocapillary equations” contains mathematical errors.

The main problem in electrocapillarity of solid electrodes is the lack of clarity in determining the surface stress and basic equations. Within the framework of the Gibbs concept of geometrical dividing surface, the “surface stress” cannot be defined because methods of continuum mechanics can be applied to a physical surface layer (of finite thickness), but not to a mathematical surface. Gibbs never used the concept of surface stress, introducing only “surface tension” for a liquid electrode and “closely related quantity” for a solid electrode. Revisiting the derivation of the Gibbs adsorption equation, we prove its applicability to solid surfaces without the limiting requirement of constant state of strain, which was undeservedly interpreted by Eriksson as a shortcoming of the Gibbs theory caused to look for other approaches to surface stress problem. A critical analysis shows that the attempts (Shuttleworth, Eriksson, Couchman, Gokhstein, Weissmuller, etc.) to create a thermodynamic definition of the surface stress (as well as the formulation of fundamental thermodynamic equations and Maxwell relations operating with surface stresses) contain mathematical defects. It is shown that confusing interpretations of some Gibbs’ concepts encountered in the literature have led to “modifications” of the Lippmann equation based on the critical error in the Gibbs–Duhem relation due to the occurrence of an extensive variable, which is inadmissible. The famous Lippmann equation should not be modified, and it remains a unique electrocapillary relation applicable to liquid and solid electrodes.

It is shown that the so-called “equation of solid-state electrocapillarity” derived by Gokhshtein from the simplest thermodynamic model, earlier used by Lippmann, is an incorrect modification that is returned to the classic Lippmann equation if to take into account the usual definition of differential capacity of the electrical double layer. Consequently, Gokhshtein’s experiments can actually confirm only the validity of the Lippmann equation (with deviations caused by physicochemical processes in the double layer, which could not be taken into account in the thermodynamic equations). The thermodynamic model is insufficient for the interpretations of these experimental results, whose understanding requires physical models of the different phenomena occurring at the electrode surface.

Low-cycle fatigue (LCF) in engineering structures is caused by a relatively low-frequency strain cycling or thermal cycling. Regardless of the fact that it is much more dangerous than high-cycle fatigue, it has not been studied enough. Coated aluminum alloys are widely used in aerospace and transportation industries, mostly because of their high toughness and strength-weight ratio and improved surface properties. The effect of one-, two- and three-layer coatings, including an inner electroless nickel layer and, additionally, electrodeposited nickel, gold and silver, on the LCF behavior of 1.6-mm-thick 6061-T6 Al alloy was studied in a strain-controlled purely bending mode at maximum plastic strain varied from 0.003 to 0.010. The lifetime of the coated alloy drastically decreases as compared to the substrate. Incipient cracks were revealed, first of all, in the electroless nickel layer and in the substrate close to its surface.

Low-cycle fatigue (LCF) of 6061-T6 Al alloy plated with nickel, gold and silver as well as thermally-cycled carbon-epoxy laminate was studied at constant strain in a purely bending mode. The tensile and fatigue properties of the alloy coated with multi-layered deposits depend on the thickness of the inner electroless nickel layer that drastically decreases the ductility of the system. Electroplating by the second ductile Ni layer increases the lifetime of the alloy in comparison with that coated only by the electroless Ni layer. Thermal cycling of the carbon fiber reinforced polymer (CFRP) composite at maximum and minimum operating temperatures of 180 C and –195.8 °C, respectively, shortens the fatigue life of samples in the high-cycle fatigue range corresponding to the number of cycles N exceeding 20,000. However, in the low-cycle fatigue region, the fatigue life of thermally-cycled laminates was slightly longer than that of the reference one, probably, due to the stress distribution between small cracks, which retards the fatigue failure and prevents fast propagation of the main crack.

For the first time, it is shown that the first and second Gokhshtein equations were originally derived by him from false fundamental equations violating criteria for applications of Maxwell relations and Legendre transforms. These equations are erroneous. For example, the direct connection between the electrode potential and charge density is actually independent of the tangential elastic strain of flat ideally polarizable electrode. The sequence of equations of Shuttleworth–Herring–Eriksson–Couchman–Jesser–Everet–Davidson–Rusanov has a common mathematical defect which consists of illegally equating the total differential to the partial differential.

Creep behavior of 40- and 80-μm-thick films of linear low-density polyethylene with four different densities produced by blowing and casting processes was investigated at room temperature (RT) and 70°C. As a criterion for ductile creep failure, strain-to-failure was chosen, which amounts to the maximum elongation characterized by necking of the whole sample. At RT under the stress of 8 MPa, strain-to-failure increases by one order of magnitude (from 0.08 to 0.80) with a decrease in density from 0.930 to 0.902 g/cm3. Processing effects creep deformation much less significantly in comparison with density. It is found that under loading at RT, some amount of orthorhombic phase in films with the densities of 0.902 and 0.912 g/cm3 transforms into the monocline phase. The intensity of a peak of this phase near the angle 2θ of 19.5° does not depend on the test duration. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Low-cycle corrosion fatigue of stainless steel 316L was investigated at room temperature in a reversible strain-controlled bending mode in air, 3.5% NaCl with pH values of 0, 3 and 6 and in doubly deionized water (pH 3). The changes of cyclic ductility parameters with changing pH reflect the changes in mechanochemical interactions, which can result either in additional plasticization (chemomechanical effect) or in the embrittlement (microcracking) during cycling loading.

The effect of processing and microstructure on the stress-corrosion–creep behavior of die-cast rheoformed and conventional AZ91D Mg alloy was studied. Rheoformed alloy has a globular microstructure as compared with a dendritic microstructure of conventional die-cast Mg alloys. The rheoformed die-cast alloy was obtained by stirring the melt during the solidification in a spinning crucible at the casting temperature 580 °C, where the solid fraction amounted to about 40–60%. Due to the difference between the microstructure of Mg alloys produced by the two methods, the corrosion rate of rheoformed AZ91D alloy in the corrosive 0.9% NaCl and in the borate buffer solutions was significantly less than that of a conventional dendritic die-cast alloy. Due to the delay of metal dissolution, creep life of anodized rheoformed alloy in 3% Na 2 SO 4 solution was more than an order of magnitude longer than that of an uncoated alloy.

A critical evaluation of mechanistically based modelling of stress corrosion cracking (SCC) known as film rupture model (FRM) has been made. The model based on “surface film rupture” is evaluated from both a mechanistic and quantitative standpoint. It is shown that although FRM is based on a real physical phenomenon, this model is not yet (and probably will never be) a correct theoretical description and therefore cannot be recognized as a true model even in those cases where film rupture events forming active–passive transitions could be able to facilitate galvanic pairs and SCC together with other motive forces (e.g., selective slip dissolution due to local excess Gibbs potential, intergranular corrosion, etc.). One of main reasons of such inconsistency is modelling without taking the role of stresses into account to the supply of strain rate providing rupture of surface oxide films (for exposing a bare metal) and the omission of a contribution of mechanochemical effect in dissolution acceleration.

This article has been retracted at the request of the Chief Editors and authors. Please see http://www.elsevier.com/locate/withdrawalpolicy . Reason: Not all identified co-authors were aware of, or approved of the publication of this article. The Editors and Publisher would like to reaffirm their commitment to providing content of the highest scientific value and will strive to avoid such instances in the future.

Received 29 November 2005; accepted 3 June 2006DOI 10.1002/app.25148Published online in Wiley InterScience (www.interscience.wiley.com).ABSTRACT: Creep and stress-relaxation of linear low-density polyethylene (LLDPE) crosslinked with b-irradia-tion was studied as a function of irradiation dose. It wasshown that both storage modulus and a-relaxation areinfluenced by irradiation. An influence of relatively lowgel content on stress relaxation was detected. However,the creep results showed an increase of the creep strainwhen the polymer is irradiated with a dose below 4 Mega-rad (MR) in comparison with a nonirradiated film. Thisincrease corresponded to the disorientation in the amor-phous phase, which takes place as a result of the film heat-ing during irradiation. This disorientation was demon-strated by differential scanning calorimetry (DSC) andX-ray analysis.

A century ago, Tafel disapproved the attempts to derive the empirical equation named after him by thermodynamic methods. He noted that his observations referred to irreversible electrochemical reactions, where thermodynamics is inapplicable. This statement seems to remain valid until today. Indeed, it is impossible as yet to predict the kinetic parameters for chemical processes by determining rate constants and reaction orders from “first principles”, unless strictly specialized and, to a great extent, artificial models are developed. Nevertheless, in this paper an attempt to derive the kinetic law of mass action from “first principles” is made in macroscopic formulation. It has turned out to be possible owing to the methods of thermodynamics of irreversible processes that were unknown in Tafel’s time.

Environment-enhanced creep, which we have called “corrosion creep” (CC), was investigated in pure Mg and die-cast AZ91D, AM50 and AS21 alloys in a borate buffer solution and 3.5% NaCl at room temperature. In contrast to the data in the air demonstrating only the first stage of creep process, in corrosive solutions, secondary and tertiary creep due to the plasticization effect of the solution was observed. The lifetime of pure Mg increases by one order of magnitude in the buffer solution in comparison with that in 3.5% NaCl. Elongation-to-fracture in the former was approximately twice as high as that in NaCl, probably, due to hydrogen embrittlement in the latter. In corrosive solutions, the creep life and elongation-to-fracture of Mg alloys decreases with increasing aluminum content from 2.3 to 8.4% in AS21, AM50 and AZ91D alloys. Cracking and final creep-rupture of pure Mg originate in a transcrystalline manner in comparison with intercrystalline fracture of the alloys. Cracks are observed in pure Mg at the primary creep stage, but their depth and amount are relatively small. The effect of environment on the creep behavior of magnesium is connected, mainly, with plasticization of metal assisted by chemical reactions. Also, anodic dissolution of Mg is enhanced by creep stress.

Corrosion fatigue tests were carried out on die-cast and extruded magnesium alloys AZ91D, AZ80, AM50, and ZK60 in air, and NaCl-based and borate solutions. N sol /N air ratios (the relative fatigue life) were used for 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). The synergistic effect of corrosion and stress on viscoelast...

In the present study the influence of the heating rate on the stability of the double bubble technological process was investigated. It was shown that increasing the heating rate decreases the stability of the process and causes the lower elongation of the films produced. The morphological transformations of linear low density polyethylene (LLDPE) film were explained using X-ray and transmission electrom microscopy (TEM) methods. The stress relaxation behavior of co-extruded LLDPElethylene-vinyl-acetate (EVA) film was studied using the relaxation time spectrum approach. The influence of vinyl-acetate (VA) content in EVA copolymers on the relaxation time spectrum was observed.

The above paper [Corros. Sci. 45 (2003) 2497] declares a general approach to describing stress corrosion cracking (SCC) mechanism and despite of the criticism of the so-called “surface mobility mechanism” (SMM) e.g., [Corros. Sci. 36 (1994) 669, Corros. Sci. 45 (2003) 2105]. The paper [Corros. Sci. 45 (2003) 2497] demonstrates inner contradictions and mutually excluding statements of SMM when fitted calculated and measured values of crack propagation rate. As shown in these Comments, the crack propagation rate calculated using SMM is only the Nabarro–Herring creep deformation rate, which can never be numerically equal to the crack propagation rate. Thus, tests undertaken by the author of SMM cannot be accepted as experimental evidence of the SMM.

The morphology and stress relaxation of coextruded five-layer LLDPE (linear low-density polyethylene)/EVA (ethylene-vinyl-acetate) copolymer films were studied. Increasing VA (vinyl acetate) content in EVA causes a decrease of shrink tension in the films, which can be explained by a decrease in amount of crystallinity. The relaxation time spectrum of the coextruded crosslinked LLDPE/EVA films is similar to the relaxation time spectrum of crosslinked LLDPE film at room temperature. However, at elevated temperatures, an additional peak appears on the spectrum of coextruded film. The cause of this peak is temperature- and stress-induced recrystallization of EVA during the relaxation test. This recrystallization was confirmed with DSC and wide angle X-ray analysis. Polym. Eng. Sci. 44:1716–1720, 2004. © 2004 Society of Plastics Engineers.

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).

Morphology and stress relaxation of oriented polyolefin films has been studied. The influence of orientation on morphology of the films has been investigated using X-ray, DSC, and TEM. The relaxation time spectrum of oriented films has been investigated. It was shown that relaxation time spectrum of composite film can be predicted if one knows the relaxation time spectrum of each component in the film. An influence of irradiation on relaxation behavior of polyethylene film was shown as well. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3424–3429, 2003

A detailed analysis of the so-called “surface mobility mechanism” (SMM) of stress corrosion cracking (SCC) is given. This SMM based on “abnormally high” surface diffusivity influenced by stress in the crack tip was proposed by J.R. Galvele in 1987 and later criticized by K. Sieradzki and F.J. Friedersdorf in 1994. However, the SMM author continues to promote his concept in recent papers, which was an incentive of the present analysis. It is demonstrated that SMM contains inner contradictions and mutually excluding statements. In conclusion, it is shown that tests undertaken by the author of SMM cannot be accepted as experimental evidences of the SMM.

The microstructure and the dislocation arrangement in the die cast AM50 magnesium alloy as well as in the stressed states have been investigated using conventional transmission electron microscopy (TEM), high-resolution TEM and energy dispersive X-ray analysis. The microstructure of the die cast AM50 alloy is found to mainly consist of α-Mg, β-Mg17Al12 and Al8Mn5 phases. Two kinds of β-Mg17Al12 particles with different sizes have been found in the stressed AM50 magnesium alloy. Besides the normal β-Mg17Al12 particles with size around several micrometers as in the die-cast AM50 magnesium alloy, some finer β-Mg17Al12 particles in the stressed states of the AM50 alloy have also been found. The finer β-Mg17Al12 particles are found to be only about tens of nanometers with oval or rod-like morphology, which may be formed during deformation. Dislocation pile-ups have been found in the stressed AM50 alloy for the first time. The spacing between each parallel dislocation in the pile-ups is only several nanometers. The dislocations are confined in the slip planes and piled up against grain boundaries. Dislocations in the networks are found to increase with deformation of the alloy. Also, dislocation networks have been found in the β-Mg17Al12 and Al8Mn5 phases as well as in the matrix in the deformed AM50 magnesium alloy. However, the dislocation pile-ups are found to be almost identical from 1.3% deformation to rupture, which explains the stable tensile yield strength of the AM50 magnesium alloy during the deformation.

In the present work, the morphology and stress-relaxation of cross-linked polyethylene films were investigated. The stress-relaxation of cross-linked films was studied as a function of temperature and as a function of the irradiation dose applied. The relaxation time spectra of cross-linked films were observed to display additional relaxation times. Irradiation dose and temperature were shown to influence the relaxation time spectrum of cross-linked and non-cross-linked films. The crystallization of cross-linked and non-cross-linked polyethylene was compared. It was shown that the lower mobility of the cross-linked molecules affects the final crystallinity.

The microstructures and the dislocation arrangements in the die cast AZ91D magnesium alloy as well as the stressed alloys have been investigated using transmission electron microscopy, high-resolution transmission electron microscopy and energy dispersive X-ray (EDX) analysis. Besides the dominant α-Mg and β-Mg17Al12 phases, Al8Mn5 and Mg5Al phases have also been found and studied in the alloy. Dislocation pile-ups have been found in the stressed AZ91D alloys for the first time. They are confined in the slip planes and piled up against the grain boundaries. The dislocation pile-ups increase with deformation till about 2.1% and then remain almost identical even deformed to higher degree. The dislocations pile-ups in the AZ91D magnesium alloy are found to be beneficial to the resistance to stress corrosion cracking of the alloy, and thereby beneficial to the mechanical properties of the alloy. Dislocation networks are found to increase with deformation in all cases. The dislocation networks have also been found in the β-Mg17Al12 phase as well as in the matrix in the deformed AZ91D magnesium alloys.

The present study describes an influence of β-radiation on morphology, mechanical properties and stress-relaxation of biaxially oriented polyethylene films. The mechanical properties and stress-relaxation of irradiated crosslinked films were studied as a function of the irradiation dose applied. The relaxation time spectra of crosslinked films were observed to display additional relaxation times. Irradiation dose of 4 megarads (MR) was found to be optimal from the viewpoint of mechanical properties. The crystallization of crosslinked and noncrosslinked polyethylene was compared. It was shown that irradiation affects the final crystallinity of polyethylene. Lower crystallinity was observed due to lower mobility of crosslinked molecules.

Potentiodynamic polarisation and impedance measurements are used to examine the corrosion behaviour of some magnesium alloys, which were previously stressed in order to establish the effects of mechanical deformation on the electrochemical reactions at the interface alloy/electrolyte. Due to the increasing demand for joint parts of magnesium alloys there is a need to perform localised machining. For this reason it is interesting to study both the surface and the cross-section. DC und AC Polarisationsuntersuchung an Magnesiumlegierungen Einflus der mechanischen Verformung Potentiodynamische Polarisations- und Impedanzmessungen werden eingesetzt, um das Korrosionsverhalten verschiedener Magnesiumlegierungen zu untersuchen, die vorher mechanisch beansprucht wurden, um die Einflusse mechanischer Verformung auf die elektrochemischen Reaktionen an der Grenzflache Legierung/Elektrolyt zu erzeugen. Auf Grund der steigenden Nachfrage nach Verbindungsteilen aus Magnesiumlegierungen ist eine lokale mechanische Bearbeitung notwendig. Daher ist es von Interesse, sowohl die Oberflache als auch den Querschnitt zu untersuchen.

The feasibility of semisolid casting process with AZ91 and AM50 magnesium alloys, which are usually used for hot- and coldchamber die-casting, was investigated in this work. Two casting methods were examined: direct casting from the melting–stirring unit and billets casting. The billets had been precast with thixotropic properties, and were heated again by an induction furnace before the casting. The apparent viscosity of the semisolid magnesium slurry during continuous cooling was found as a function of the casting temperature. Viscosity tests show that the appropriate casting temperatures in the two-phase region were in the range of 595–575 C for AZ91 alloy and 620–614 C for AM50 alloy. At casting temperature of 585 C, AZ91 exhibited maximum density and the highest standard mechanical properties. AM50 alloy demonstrated the relative poor mechanical properties in the two-phase region. The toleration of heat treatment of semisolid AZ91 alloy with a 1.8-fold increase in the elongation-to-fracture was observed. No significant differences of the densities and the standard mechanical properties of the alloys between direct or billet castings were demonstrated. 2002 Elsevier Science Ltd. All rights reserved.

Potentiodynamic polarisation and impedance measurements are used to examine the corrosion aspects of some Mg-based alloys, which were previously stressed in order to established the effect of mechanical deformation on surface electrochemical reactions. A first approach was made for the unstressed alloys. The electrochemical tests were carried out in a sodium borate buffer solution.

To study the fatigue life of die-cast and extruded AZ91D, AM50 and AZ31 magnesium alloys, corrosion fatigue tests were carried out using a rotating beam type fatigue machine. Corrosive environment (3.5% NaCl) significantly decreases fatigue life of alloys, especially for extruded alloys. The fatigue data at high stresses were analyzed using fitting equations. Extruded alloys show a higher sensitivity to the action of NaCl solution in comparison with die-cast alloys; however, their corrosion fatigue life is longer than that of die-cast alloys. Corrosion fatigue behavior of Mg alloys correlates with their mechanochemical behavior. The latter was studied by the polarization measurements of the dissolution rate of strained alloys. TEM observations confirmed that the maximums on the curves of Mg dissolution rate dependence on the strain in NaCl solution appeared at the work-hardening stages due to the creation and destruction of dislocation pile-ups.

Both creep and corrosion resistances are significant problems in the application of magnesium alloys. The synergistic effect of corrosion and stress on the viscoelasticity of magnesium alloys named corrosion creep has been studied in die-cast AZ91D (Mg–9%Al–1%Zn) and AM50 (Mg–5% Al–0.4% Mn) alloys in air and in the borate buffer solution. The highest sensitivity to creep in the corrosive environment is observed in the alloy with the highest Al content. An electrochemical study under a tensile strain demonstrates a good correlation with corrosion creep tests.

(2001). Processing Effect on Mechanical Properties of Die Cast Magnesium Alloys. Materials Technology: Vol. 16, No. 2, pp. 126-132.

Creep and stress relaxation resistance of the most common die-cast Mg alloy AZ91D (Mg-9% Al-1% Zn) are influenced by both casting temperature and injection rate as well as by die temperature and porosity. Relationships between viscoelastic properties of Mg alloy at 150 °C and the parameters of die-casting technology are obtained and presented as simple contour plots (isograms). These properties can be improved by reducing casting temperature and increasing injection rate. When fabricating complicated thin-wall components, castability of the alloy can be diminished due to a fast temperature drop. In this case, casting temperature should be higher, whereas injection rate can be reduced. Porosity seems to be the most important characteristic of die-cast alloy microstructure affecting its viscoelastic properties. Coarse β-phase precipitates do not affect creep and relaxation characteristics of die-cast AZ91D alloy.

A new synergistic effect of corrosion and stress on the viscoelasticity of pure magnesium and magnesium alloys has been shown. This phenomenon named corrosion creep has been studied in 99.9653% Mg, die-cast AZ91D (Mg–9% Al–1% Zn), AM50 (Mg–5% Al–0.4% Mn), and AS21 (Mg–2.3% Al, 0.23% Mn, 1.10% Si) alloys. Creep tests were carried out at 25°C in air and in the borate buffer aqueous solution (pH 9.3). It is found that the highest sensitivity to creep in the corrosive environment is observed in the alloy with the highest Al content. This agrees with the data obtained earlier in the study of mechanoelectrochemical behavior and corrosion fatigue of Mg alloys. However, in air, the creep behavior of all alloys at room temperature is approximately the same. Creep life of pure magnesium and its alloys significantly decreases in a corrosive environment. Corrosion-creep cracks filled with magnesium hydroxide particles were observed by SEM–EDS analysis at the surface of AS21 alloy. The thickness of the oxide layer defined by AES in samples of AZ91D, AM50, and AS21 alloys placed for 2 h into the borate solution amounts to ∼540, ∼1320, and ∼1440 nm, respectively. This can be explained with the account for surface phenomena.

We have studied the microstructure, phase composition and morphology of the intermetallic β-phase in the surface layer of the most widespread magnesium alloy AZ91D (Mg–9 wt.% Al–1 wt.% Zn) used in pressure die casting. Auger electron spectroscopy (AES), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM) and optical microscopy have been applied. The surface of the AZ91D Mg alloy consists of an oxide-metallic film with a thickness of about 0.15 micron containing Mg and Al oxides. Prolonged aging in air at 200°C promotes an increase in the MgO/Al 2 O 3 ratio from 9±2 to 14±2. The aluminum concentration gradient in the surface layer is rather significant. The external layer of as-cast specimens contains up to 32 at.% Al, whereas α-Mg grains in the bulk contain, on the average, about 5 at.% Al. Aging leads to a substantial increase in the surface concentration of aluminum at the expense of the acceleration of its diffusion and the intensification of supersaturated solid solution decomposition. During creep tests at elevated temperatures the morphology of the β-phase is significantly affected by strain and, to a lesser extent, by the casting temperature.

The mechanical properties and mechanoelectrochemical effect (the effect of mechanical deformation on the surface electrochemical reactions) were investigated for some Mg-based alloys supposing that aluminum alloying influences them. A simple method of testing mechanoelectrochemical behavior of metals was developed. Potentiostatic polarization measurements on stressed electrode were carried out in chloride electrolyte. The correlation between the mechanoelectrochemical behavior and strain hardening stages is observed during plastic deformation. Maximum mechanoelectrochemical effect is achieved under intense strain hardening in the initial portion of this stage. The experimental observations are explained theoretically.

Mechanopolymerization of pentabromobenzyl (mono)acrylate (PBB-MA) on the surface of inorganic fillers Mg(OH)2 and CaCO3 was studied. The role of activated surface of fillers was investigated using DSC and FTIR. The influence of milling time and of the filler chemical content on polymerization starting temperature and polymerization enthalpy was studied using DSC. It was shown that an increase of the filler concentration leads to a higher maximum conversion degree. The correlation between conversion kinetics and polymerization enthalpy of the material notpolymerized during milling was shown.

The thermal polymerization of pentabromobenzyl (mono)acrylate (PBB-MA) on the surface of the inorganic fillers Mg(OH)2 and CaCO3 was studied. FTIR spectroscopy and extraction of the polymer in bromobenzene show that polypentabromobenzyl acrylate (PBB-PA) was mostly grafted on the surface of Mg(OH)2. Thermal analysis (TG, DSC, isothermal DSC (IDSC)) demonstrated an increase in polymerization starting temperature, and differences in polymerization enthalpy and apparent activation energy when an inorganic filler is added. These differences depend on the chemical composition of the filler used.