关键词： Micro-milling   Grey relational analysis   TOPSIS   Weight coefficient   Multi-objective optimisation   Sustainable production  

摘要： The present research attempts to maximise the overall performance of micro-milling process while machining Mg-3.0Zn-0.7Zr-1.0Cu alloy and its alumina composites. Three performance measures (surface quality, cutting forces, and tool wear) is used for the assessment. Using a Taguchi L18 orthogonal array, eighteen experiments are carried out to test the effect of three levels of spindle speed, feed per tooth, and cutting depth. Grey relational analysis (GRA) and techniques for order of preference by similarity to ideal solution (TOPSIS) are employed to optimise the parameters. In addition, the equal weight method and entropy weight method (EWM) in combination with the analytic hierarchy process (AHP) are used to assign weights to the parameters. The GRA and TOPSIS results yielded the same optimal parameter conditions for maximising the micro-milling performance while using two different weight-assigning methods. Based on the predicted closeness value results, the GRA method is the most efficient for multi-objective optimisation.

关键词： Biomedical Mg implants   Corrosion   Conversion coatings   Non-conversion coatings   Osseoconductive functionality   In vivo stability  

摘要： Several magnesium alloys are increasingly used for a variety of biomedical applications, owing to their favorable mechanical and biomedical properties. However, in vivo corrosion in aqueous environment including Cl ion-rich extracellular fluid (ECF) requires the application of protective coatings as well as the development of advanced alloy formulations with increased corrosion resistance and uniform, non-localized dissolution modes. This contribution reviews recent promising approaches towards improved biostability of Mg alloys during in vitro contact with simulated body fluid (SBF) as well as in vivo exposure to ECF. Emphasis is being put on surface coatings for corrosion protection as well as on functional osseoconductive coatings that stimulate tissue ingrowth.

关键词： Friction stir processing (FSP)   Al-Mg alloy   Microstructure   Corrosion resistance   Electrochemical behavior  

摘要： This article deals with the corrosion behavior of friction stir processed aluminum-magnesium alloys undergoing electrochemical measurements, including potentiodynamic polarization and electrochemical impedance spectroscopy. The effects of friction stir processing (FSP) critical parameters such as the rotational tool speed (w in the range of 800-1400 rpm) and traverse velocity (v in the field of 50-200 mm/min) along with varying cooling rates imposed using submerged cooling medium (air, water/dry-ice mixture, and liquid nitrogen) on the microstructural features and mechanical properties of Al-Mg alloys in two tempering states of annealed and wrought were characterized. Then, by assessing the electrochemical behavior of the friction stir-modified stirred regions produced using varying cooling rate and initial temper, a correlation between the microstructural details with the mechanical and chemical properties was established. The experimental results revealed the significant grain refinement down to similar to 1 um following FSP treatment by controlling the processing conditions, which had a detrimental impact on the electrochemical behavior due to the activation of grain boundary corrosion phenomenon. The primary tempering state of alloy in the form of stored strain energy played a critical role by controlling the fraction of sub-boundaries and recrystallized grains upon FSP modification. The inferior electrochemical property reported for the FSP treated annealed Al-Mg alloy under processing conditions of w= 800 rpm and v = 200 mm/min, as the less noble structure with the highest corrosion rate (CR) of 0.01814 mm/year.

关键词： Neutron diffraction   Stress localisation   Slip systems   Self-consistent modelling   Elastoplastic deformation   Magnesium alloy  

摘要： The main purpose of this work is to develop neutron diffraction methodology in order to determine stresses localised in polycrystalline grains during elastoplastic deformation, directly from experiment. As a result, for the first time, the von Mises stress for chosen grain orientations and Critical Resolved Shear Stresses (CRSS) for active slip systems were unambiguously measured without the help of crystallographic models, which introduce different theoretical assumptions. The stresses measured for groups of grains and the determined CRSS values are important characteristics of a material, which allow to study plastic deformation in textured material at different scales: slip system and grain, which play a key role in mechanical properties and formability of the material. The new method was successfully tested and applied to textured AZ31 alloy subjected to tensile deformation and the components of stress tensor were for the first time determined from measured lattice strains corresponding to chosen orientations of crystallite lattice. The obtained results positively verified hypotheses that, during plastic deformation, a large difference in the hardness as well as in the localised stresses occurs for grains having different lattice orientations. It was found directly from experiment that, the activation of basal glide, having small CRSS, does not lead to significant plastic deformation, and the activation of other non-basal systems (with higher CRSS) induces the development of plasticity at the macroscopic scale. The early plastic deformation occurring due to slip on basal system is small but it can destructively affect fatigue life, limiting applicability of the material for structural components. Finally, the comparison of experimental results with a modified version of Elastic-Plastic Self-Consistent (EPSC) model showed its capability to simulate the mechanical behaviour of such materials.

关键词： Magnesium alloy   Torsion   Swift effect   Strain hardening   Twinning  

摘要： The mechanical response and microstructure evolution in a rolled AZ31B magnesium alloy were experimentally characterized using companion thin-walled tubular specimens under free-end monotonic torsion. The tubular specimens were made with their axes along the normal direction of the rolled magnesium plate. The shear stresss-hear strain response shows a subtle sigmodal shape that is composed of four distinctive stages of strain hardening. Basal slips and tension twinning are operated throughout the shear deformation. Both tension twinning and compressing twinning are favored. Growth and interaction of tension twins with multiple variants lead to formation of twin-twin boundaries (TTBs). The collective hardening effects by twin boundary (TB) and TTB result in a unique rise of the strain hardening rate in Stage II and III. In addition to primary twins, tension-compression double twins and tension-compression-tension tertiary twins with detectable sizes are observed in the tension-twin favorable grains whereas compression-tension double twins are detected in the tension-twin unfavorable grains;all of which become more observable with the increasing shear strain. During Stage IV deformation where TTB formation exhausts, non-basal prismatic slips become more significant and are responsible for the progressive decrease in strain hardening rate in this stage. Swift effect, which is commonly observed in textured materials, is evidenced under free-end torsion. The origin of Swift effect is confirmed to be dislocation slips at a shear strain less than 5% but is predominantly due to tension twinning at a larger plastic strain.

关键词： Coatings   Polymers   Electrochemistry   Corrosion inhibiters   Polyaniline   Praseodymium   Corrosion inhibition   AZ31 magnesium alloy  

摘要： Purpose The purpose of this study was to evaluate the possibility of using conductive polymers such as polyaniline (PANI) as corrosion inhibitors for metals. Design/methodology/approach In this study, the effect of the addition of praseodymium (Pr3+) cations on the corrosion inhibition performance of PANI for AZ31 magnesium alloy was appraised through electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests. Findings The results of EIS and potentiodynamic polarization tests indicated the improvement of corrosion resistance of AZ31 during different immersion times. Research limitations/implications This anti-corrosion ability of PANI/Pr(3+)composite applies as non-toxic environmentally friendly corrosion inhibitor on the self-healing corrosion protection properties. Practical implications The conductive polymers are interested for many industries. The reported data can be used by the formulators working in the R&D departments. Social implications The anti-corrosion ability of PANI/Pr(3+)composite present a novel and high effective route against metal corrosion besides application of toxic corrosion. Originality/value The application of titanium dioxide coating in the field of architectural heritage is a great challenge. Therefore, the main objective of this study is to study the synthesis, characterization and corrosion inhibition performance of Pr(3+)cations doped PANI nano-fibers as an anti-corrosion additive for AZ31 magnesium alloy in 3.5 Wt.% NaCl solution.

关键词： Semi-solid extrusion   Magnesium alloys   Mechanical properties   Microstructure   Texture  

摘要： The microstructure evolution and mechanical properties of AZ31 magnesium alloy during semi-solid extrusion (SSE) has been studied and compared with traditional extrusion (TE). The results show that non-equilibrium crystallization and plastic deformation occur simultaneously in the semi-solid extrusion process. Throughout the SSE process, the nucleation rate of new fine grains is significantly higher than that of the TE, which is the result of combined nucleation of crystallization and dynamic recrystallization. Twinning can be hardly activated during the SSE process, because the restraint between deformed grains is largely reduced due to the good fluidity of the semi-solid Mg alloy. The Mg alloys extruded by the SSE is characterized for homogeneous microstructure with fine grain size, weakened texture and improved mechanical properties.

关键词： AZ31B magnesium Alloy   Asymmetric rolling   Shear deformation   Homogeneity   Twinning   Mechanical properties  

摘要： In this study, the changes in the microstructure, texture, and mechanical properties of the AZ31B magnesium alloy sheet after asymmetric rolling (ASR) in different shear deformations during each pass are reported. A high shear strain is induced along the sheet thickness when the velocity ratio of the upper and lower rollers is 1.8. In the case of the sheet processed via ASR in the reverse shear deformation along the rolling direction (RASR), the grain refinement, weak basal texture, and improved structural homogeneity result in better mechanical properties than those of the sheet processed via symmetric rolling (SR). However, in the case of the sheet processed via ASR in the single shear deformation along the rolling direction (UASR), shear bands containing dynamically recrystallized grains and larger numbers of dislocation are formed, tilting the peak intensity of the pole figure away from the normal direction. Moreover, the shear band with an average grain size of 5 mu m causes severe structural inhomogeneity, which results in bad mechanical properties than the other two sheets. Furthermore, the twin mode changes from the double twin of the SR sheet to the extension twin of the ASR sheet under shear strain. The extension twin contributes to the optimization of the mechanical properties. Finally, the strength and elongation of the sheets processed via RASR are simultaneously improved to 250.3 MPa and 12.5%, respectively.

关键词： Magnesium alloys   High-pressure torsion   AM60   Shear punch test   Texture   Hardness  

摘要： The evolution of the microstructure, crystallographic texture and hardness of an AM60 magnesium alloy was studied in the center and the edge parts of disks processed by high-pressure torsion (HPT) technique at room temperature. In addition, the mechanical properties were also tested by shear punch test (SPT). The number of HPT turns varied between 1/2 and 10. It was found that the grain size of the initial extruded material (similar to 16 mu m) decreased to similar to 2 and similar to 0.8 mu m at the disk center and edge, respectively, even after 1/2 turn of HPT. Ten turns of HPT resulted in further grain refinement to similar to 1 and similar to 0.23 mu m at the disk center and edge, respectively. The dislocation density saturated even after 1/2 turn with the value of similar to 11 x 10(14) m(-2). The maximum value of the hardness was similar to 1300 MPa that was measured at the edge of the disk deformed for 1/2 turn. Despite the practically unchanged grain size and dislocation density, the hardness decreased between 3 and 10 turns which can be explained by texture softening. A good agreement was observed between the yield strength estimated as one-third of the hardness and the values calculated from the dislocation density, grain size and texture. The difference between the microstructure and hardness obtained for AM60 samples processed by HPT and equal channel angular pressing (ECAP) is discussed.