AZ31 Magnesium Alloy Research Articles

Investigation of structural properties of forsterite coating on AZ91 magnesium alloy by sol-gel method

This study examined the synthesis and characterization of a nanostructured forsterite coating on a biodegradable AZ91 alloy to enhance its bioactivity. The coating was applied using sol-gel technique, resulting in a homogeneous and crack-free surface as confirmed by scanning electron microscopy. X-ray diffraction was used to identify the phases present in the coating, which confirmed the presence of forsterite particles with an average size of 35 nm. To evaluate the effectiveness of the coating, potentiodynamic polarization electrochemical tests were conducted in simulated body fluid (SBF), which showed that the corrosion current density decreased from 11 μA cm−2 for uncoated samples to 4.3 μA cm−2 for coated samples. Moreover, the surface of the coated magnesium alloy showed fewer cracks and cavities after being immersed in SBF for 672 h. Given that the early degradation of magnesium alloy poses challenges for prostheses and bone stabilizers, this coating could promote bone healing and positive interaction with bone tissue while preventing toxicity from metal ions.

Hydrothermal synthesis and characterization of calcium phosphate-based coatings on AZ31 magnesium alloy

Abstract This study aims to analyze the influence of process parameters used for hydrothermal synthesis of CaP coatings on their properties and to improve their corrosion resistance and biocompatibility compared to the substrat AZ31. The parameters monitored were deposition time, pH of the reaction mixture, and concentration of precursors in the reaction mixture. For the deposited CaP coatings on AZ31 magnesium alloy, the surface morphology and the number of structural defects were evaluated using scanning electron microscopy. Electrochemical corrosion properties were evaluated using polarization techniques in Hank’s solution. The results showed that the best properties were obtained for the sample prepared in a reaction mixture at 120 °C, pH 5 for a deposition time of 120 min, when the concentration of precursors in the reaction mixture was 0.30 mol/l Ca(NO3)2·4H2O and 0.28 mol/l NH4H2PO4. Under these conditions, the best electrochemical corrosion properties were achieved.

Prediction of mechanical strength of magnesium alloy AZ31 with calcium addition using a neural network based model

The aim of the research is to develop a neural network model to predict the mechanical strength of AZ31 magnesium alloy in addition with Calcium. This would help researchers or academicians to fabricate the magnesium alloy AZ31+x wt. % Ca which finds more importance in making biodegradable implants in orthopedic surgery. As the yield strength of human bone lies between 104.9 – 114.3 MPa whereas for pure Mg it is very lesser, it is needed to make alloys suitable for biomedical applications which are to be satisfied with their mechanical properties and biocompatibility. An artificial neural network-based model is used to predict the mechanical properties of Mg alloys AZ31+x wt. % Ca with compositions of Al, Zn, Mn and Ca as countable parts with various proportions. The compositions and properties of twenty different as cast alloys were used for training and prediction of the desired mechanical properties using Artificial Neural Network and the outputs are compared with the experimental results. The results show that the Levenberg-Marquardt (LM) algorithm serves better in prediction of mechanical properties of Mg alloys AZ31 and AZ31+1 wt. % Ca. Also the results were found significant at 90%, 95% and 99% confidence limits.

Effect of process conditions for the preparation of a manganese-based coating on the surface of AZ31 magnesium alloy

Abstract Manganese-based coatings on AZ31 magnesium alloy with Mg(OH)2 interlayer were prepared by hydrothermal reaction under different process conditions (temperature, time, and concentration). The harsh reaction conditions provided coatings with defects. These defects enabled the corrosive environment penetrated to the magnesium alloy which impaired the corrosion properties of AZ31 alloy. Optimal conditions included a temperature of 120 °C, 0.25 M MnCl2, and a reaction time of 1 h. The prepared coating was mainly composed of Mn3O4, which consisted of nanosized crystals of polyhedral shape. Potentiodynamic polarization measurements showed that the coating had very good corrosion resistance in 0.15 M NaCl. Future work will focus on the potential use of the manganese-based coating in biomedical applications.

Comparison of the effects of submerged laser peening, cavitation peening and shot peening on the improvement of the fatigue strength of magnesium alloy AZ31

Comparison of the effects of submerged laser peening, cavitation peening and shot peening on the improvement of the fatigue strength of magnesium alloy AZ31

Ductility enhancement mechanism of AZ31 magnesium alloy with through-thickness symmetrical gradient structure prepared by hard plate rolling

The optimal configuration of strength and ductility was the first choice in Mg-alloys plate forming. A rolling method with adding the hard plate and unique component structure design was proposed to achieve a symmetrical gradient structure from two upmost surfaces to the center of the AZ31 Mg-alloys plate during a single rolling pass. The microstructure evolution and mechanical properties of symmetrical gradient structure plates were studied. The results indicate that Mg-alloy plates' strength and tensile ductility reached 267 MPa and 26.1%, respectively. In the fine-grain region, the proportion of high-angle grain boundary was 56.4%, and the recrystallization structure was 57.3%. In the coarse-grain region, high-grain boundaries and recrystallization decreased to 42.9% and 42.1%, respectively. Both prismatic slip and pyramidal slip in the CG region were easier to initiate, which leads the interaction of multidirectional twins. The geometrically necessary dislocations mainly accumulate at the boundary of the different region. The fracture morphology showed a gradient distribution of dimples. The crack was deflected in the process of extension, which also leads high ductility of Mg-alloy. The design strategy provides a new idea for producing the high-performance plate with through-thickness symmetrical gradient structure.

Numerical optimization of billet diameter in the wide-spread and split extrusion process

The research object was the wide-spread shunt extrusion production of large-diameter thick-walled AZ31 magnesium alloy pipe with 360mm outer diameter and 10mm wall thickness. Based on the DEFORM-3D finite element software platform, the simulation study on the influence of billet diameter on extrusion pressure was carried out to provide theoretical support for the reasonable selection of equipment tonnage. The results show that the peak extrusion pressure increases with the increase of billet diameter, and the increasing speed is accelerated. By reducing the billet diameter, the peak extrusion pressure can be gradually reduced from 4800 tons to 2200 tons, and the maximum extrusion cargo can be saved by more than 50%. If 3600 tons extruder is used, the billet diameter should be less than 325mm; If 2500 tons extruder is used, the billet diameter should be less than 285mm.

Mechanism of plasticity enhancement of AZ31B magnesium alloy sheet by accumulative alternating back extrusion

Accumulative alternating back extrusion was a potential fine-grain modification method. In this paper, it was an innovative attempt to develop high-performance magnesium alloy sheet by this process. Under the condition of 350 K, commercial AZ31 magnesium alloy was made into billet by accumulative alternating back extrusion, and then extruded into fine-grain magnesium alloy sheet. Through a systematic study of its microstructure and mechanical properties, the results showed that the initial state had an important influence on the evolution of the structure during extrusion. After accumulative alternating back extrusion to produce the billet, the grain size of the sheet obtained by extrusion was significantly refined, which was related to the accumulation of deformation and grain refinement during the alternating loading process. Grain refinement caused the proportion of dynamic recrystallization inside the sheet with 2 cycles of accumulative alternating back extrusion to drop to 27%. With the increase of extrusion cycles from 2 to 4, the high density of dislocations led to an increase in the proportion of dynamic recrystallization and finer grains. The texture changed from strong basal texture to weak bimodal texture. The results of uniaxial tensile test show that due to grain refinement and texture change, the yield strength was significantly reduced, and the plasticity was significantly improved. It was verified that accumulative alternating back extrusion was meaningful for subsequent processing, and it also provided scientific guidance for the development of fine-grained magnesium alloy sheet.

Deep drawing formability of AZ31 magnesium alloy based on magnetorheological elastomer support

AbstractIn this paper, the flexible support mould is designed by using magnetorheological elastomer (MRE) to assist in the deep‐drawing of magnesium alloys. Based on the magnesium alloy mechanical tensile test and magnetorheological elastomer regular force experiments, the deep‐drawing process of AZ31 magnesium alloy supported by support mould was numerically simulated by finite‐element analysis software ABAQUS. By varying the current input to the excitation coil to change the magnetic induction intensity and thus adjust the magnetic normal force of the magnetorheological elastomer, then using magnetic normal force to complete the auxiliary sheet metal deep‐drawing. The results show that, compared with the unsupported mould, the supported mould can effectively reduce the maximum thinning rate of magnesium alloy on the original basis, thus effectively increasing the ultimate depth of magnesium alloy deep‐drawing. It can replace the original buffer device, effectively solution the problem of pulling and cracking at the bottom of magnesium alloy caused by the original excessive damping force, and improve the yield rate of workpiece.

Strength-ductility balance of AZ31 magnesium alloy via accumulated extrusion bonding combined with two-stage artificial cooling

AZ31 Mg alloy with heterogeneous bimodal grain structure (smaller grain size of 5–20 µm and coarser grain size of 100–200 µm) was subjected to accumulated extrusion bonding (AEB) at 250 ℃ combined with two-stage artificial cooling in this work, viz. local water cooling and artificial cooling. The microstructure developed consecutively as a result of discontinuous dynamic recrystallization (DDRX) for the AEBed samples. {10–12} tensile twinning also played an important role for the AEB with local water cooling at the initial extrusion stage in the container. Local water cooling could further reduce the DRXed grain size to ~ 2.1 µm comparing that without water cooling. And the grain growth rate was reduced by artificial cooling out of extrusion die. Under the combination of two-stage cooling, the fine DRXed grains at sizing band were almost retained with average grain size of ~ 2.3 µm after the sheet out of extrusion die, and the unDRXed grains with high residual dislocation density accumulation were also reserved. The tensile tests results indicated that a good strength-ductility balance with a high ultimate tensile strength (319 MPa vs. 412 MPa) and fracture elongation (19.9 % vs. 30.3%) were obtained. The strength enhancement was mainly owing to the grain refinement and local residual plastic strain reserved by the artificial cooling. The excellent ductility originated from fine DRXed microstructure and ED-tilt double peak texture.

Characterization of Mg–9Al–1Zn-0.2Mn alloy tubes processed by a new modified tube cyclic expansion extrusion (M-TCEE) process

In this study, a new modified tube cyclic expansion extrusion process named M-TCEE was utilized for producing tubes with ultrafine grained (UFG) microstructure and improved properties. In M-TCEE process, the utilization of a moving mandrel inside the hollow tube during the process provides the possibility of using bulk rod-shaped punch, instead of hollow tubular punch which has been used in conventional TCEE process. This leads to that a higher pressing load can be applied to the material without the risk of punch buckling. So, the production of longer and larger tubes, which needs a higher required pressing load, can be performed easier in M-TCEE process. In current study, the capabilities of M-TCEE process in improving microstructure, mechanical properties and corrosion resistance of the Mg–9Al–1Zn-0.2Mn magnesium alloy tubes were investigated. The results showed that after two passes of M-TCEE process, the yield strength increased from 36 MPa to 137 MPa (3.8 time greater), the ultimate tensile strength increased from 73 MPa to 265 MPa (3.6 time greater) and the ductility was enhanced from 11.2% to 20.2% (1.8 time greater). Three passes of M-TCEE led to improving hardness from 54 HV to 99 HV (1.83 time greater). Also, corrosion results revealed the capability of the M-TCEE process in improving the corrosion resistance of AZ91 tubes. It seems that the M-TCEE process can produce ultrafine-grained AZ91 magnesium alloy tubes with significant mechanical properties and improved corrosion resistance.

Corrosion behavior of as-cast AZ91 magnesium alloy with VN particle additions in NaCl solution

The microstructures and corrosion behavior of the as-cast AZ91−xVN (x=0, 0.25, 0.5 and 1 in wt.%) alloys were investigated using optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements. The results showed that VN can significantly refine and modify the microstructures of AZ91−xVN alloys. The corrosion resistance of the AZ91 alloy was first improved and then deteriorated with the addition of VN particles. The superior corrosion resistance of the as-cast AZ91−0.25VN alloy with the lowest corrosion rate (PW=(1.47±0.06) mm/a) was attributed to the additional grain boundaries. With the further increase of VN content, the amount of the lamellar β-Mg17Al12 precipitation phase increased, and thus the galvanic corrosion between β phase and the α-Mg matrix was promoted, resulting in the deteriorated corrosion resistance of the alloys.

Effect of Cryogenic Time on Microstructure and Properties of TRCed AZ31 Magnesium Alloy Sheets Rolled during Cryogenic Rolling

Rolling experiments of TRCed AZ31 magnesium alloy with different cryogenic treatment time were carried out to study the evolution mechanism of its microstructure and mechanical properties. The experimental results showed that with the increase in cryogenic time, the grain size of the sheets after cryogenic rolling was significantly refined, and the dislocation density and texture strength were greatly weakened. The combined effect led to a significant increase in the elongation and tensile strength of the sheet after cryogenic rolling. The tensile strength, elongation and average hardness of the sheet increased from 282.6 MPa, 8.2%, and 54.6 HV to 305.4 MPa, 16.3%, and 62.8 HV, respectively. Therefore, when the cryogenic treatment time was 60 s, the performance of the rolled sheet was the best. At the same time, the appearance of dimples after cryogenic rolling led to a change of the fracture mechanism, which was also the key to the improvement of the sheet elongation.

Correction: The effects of homogenization treatment on wear resistance of AZ61 magnesium alloy fabricated by extrusion-shear process

Correction: The effects of homogenization treatment on wear resistance of AZ61 magnesium alloy fabricated by extrusion-shear process

Modeling the correlation between texture characteristics and tensile properties of AZ31 magnesium alloy based on the artificial neural networks

This work is aimed to investigate the relationship between the texture and tensile properties of the AZ31 Mg alloy by the machine learning method. The texture characteristics parameters, namely the maximum pole intensity (Imax), texture dispersion (D), and texture directivities along the longitudinal direction (PLD) and transverse direction (PTD), are extracted from the (0002) pole figures of the AZ31 Mg alloy. An artificial neural networks (ANN) model to describe the relationship between the texture characteristic parameters and tensile properties is constructed and trained by the data collected from the literature. To validate the reliability and generalization performance of the ANN, 6 samples with different texture characteristics are prepared, and their textures and tensile properties are evaluated through electron backscattered diffraction (EBSD) measurement and uniaxial tensile test, respectively. The results indicate that the ANN model exhibits good prediction performance in yield strength and elongation of the AZ31 Mg alloy when it is applied to the new cases. The correlations between the texture characteristics and tensile properties are analyzed according to the ANN-predicted results. The maximum pole intensity and texture dispersion significantly influence the tensile properties of the AZ31 Mg alloy. With increasing the Imax or decreasing the D, the strength is increased but the elongation is reduced. As increasing the texture directivity along the LD, the tensile properties of the AZ31 Mg alloy show non-monotonic changes. This research presents a correlation model between the texture and mechanical properties of the Mg alloy, which contributes to the development of high-performance Mg alloys.

Research on deformation mechanism of AZ31 magnesium alloy during uniaxial compression

The effects of the non-basal slip and twinning modes on the mechanical behaviour and texture evolution of as-extruded AZ31 alloys during uniaxial compression at room temperature have been investigated by experiments and Visco-Plastic Self Consistent (VPSC) modelling. The results show that the activation of pyramidal slip and {10-11} contraction twinning (CT) can reduce the strain hardening rate in the later stage of compression. And the prismatic slip has a significant effect on the strain hardening rate, the activation of {10-12} extension twinning (ET) can significantly reduce the strain hardening rate and the compressive yield strength. Increased activity of the {10-11} CT causes the pole density transfer to the normal direction (ND) in the {0002} pole figure.

Joining magnesium and aluminum alloy sheets by a novel hole hemming process

The use of magnesium alloys represents a novel trend in the automotive industry, being used to manufacture high performance vehicle structures. These alloys possess the lowest density among all structural metals. However, the use of joining processes based on plastic deformation of magnesium alloys is restricted by the low formability of these materials at room temperature. In this research work, a novel joining process, called hole hemming, is developed for attaching magnesium AZ31 and aluminum AA6082-T4 alloy sheets in which only one of the sheets should be sufficiently ductile and there is no need for heating or using additional elements, such as rivets. Firstly, the fracture limits of the materials were characterized under different loading states. Then, the process for joining the mentioned material combination was designed with the support of finite element analysis and the critical regions prone to fracture and their loading paths were specified. In addition, the influence of process parameters on the mechanical interlock was investigated to determine process windows. A flexible tool was then developed and, for the first time, novel hole-hemmed joints were manufactured with different process parameters to thoroughly evaluate the performance of the designed process. Finally, single-lap joints were tested under shear loads. The results of this tests show that the novel hole hemming process can suitably join the magnesium and aluminum alloy sheets, with the hole-hemmed joints supporting a maximum load of 2.9 kN with a gradual failure mechanism of hole bearing. Thus, the hole hemming process is shown to be a viable technique for joining materials with very different formability.

Effect of Aging on Corrosion Resistance of AZ31 Magnesium Alloy

Effect of Aging on Corrosion Resistance of AZ31 Magnesium Alloy

Environment-assisted cracking of AZ31 magnesium alloy in a borate buffer solution containing ammonium thiocyanate under various potentials

The environment-assisted cracking behavior of AZ31 magnesium alloy was investigated using tensile tests at cathodic and corrosion potentials in a Na2B4O7∙10H2O solution containing NH4SCN and in air. Although the mechanical properties of the AZ31 with an initial strain rate of 10−4 s−1 were independent of the environments, those degraded in the solution with an initial strain rate of 10−6 s−1. The total elongation became smaller at higher potentials. The average hydrogen absorption rate increased with a positive potential shift. These facts imply that environment-assisted cracking became more severe under relatively high potential owing to corrosion accompanied by enhanced hydrogen absorption.

Optimization of CMT Characteristic Parameters for Swing Arc Additive Manufacturing of AZ91 Magnesium Alloy Based on Process Stability Analysis.

The droplet transfer behavior and stability of the swing arc additive manufacturing process of AZ91 magnesium alloy based on the cold metal transfer (CMT) technique were studied by analyzing the electrical waveforms and high-speed droplet images as well as the forces on the droplet, and the Vilarinho regularity index for short-circuit transfer (IVSC) based on variation coefficients was used to characterize the stability of the swing arc deposition process. The effect of the CMT characteristic parameters on the process stability was investigated; then, the optimization of the CMT characteristic parameters was realized based on the process stability analysis. The results show that the arc shape changed during the swing arc deposition process; thus, a horizontal component of the arc force was generated, which significantly affected the stability of the droplet transition. The burn phase current I_sc_wait presented a linear function relation with IVSC, while the other three characteristic parameters, i.e., boost phase current I_boost, boost phase duration t_I_boost and short-circuiting current I_sc2, all had a quadratic correlation with IVSC. A relation model of the CMT characteristic parameters and IVSC was established based on the rotatable 3D central composite design; then, the optimization of the CMT characteristic parameters was realized using a multiple-response desirability function approach.