Microstructure Of AZ31 Magnesium Alloy Research Articles

Phase Field Simulation of the Effect of Second Phase Particles with Different Orientations on the Microstructure of Magnesium Alloys.

In this study, the phase field method has been used to study the effect of second phase particles with different shapes and different orientations on the grain growth of AZ31 magnesium alloy, after annealing at 350 °C for 100 min. The results show that the shape of the second phase particles would have an effect on the grain growth; the refinement effect of elliptical particles and rod-shaped particles was similar, and better than the spherical particles; the spatial arrangement direction of the second phase particles had no significant effect on the grain growth. On the other hand, when the microstructure of AZ31 magnesium alloy contained second phase particles with different shapes, the effect of mixing different shapes of second phase particles on the grain refinement was enhanced gradually with the decrease im the volume fraction of spherical particles.

Enhanced mechanical behavior and corrosion resistance of AZ31 magnesium alloy through a novel solid-phase processing

In this work, a novel solid-phase processing; namely, shear assisted processing and extrusion (ShAPE) was used to modify the microstructure of AZ31 magnesium alloy, which simultaneously improved corrosion resistance along with mechanical properties compared to wrought AZ31 alloys. A noble breakdown potential, higher polarization resistance, and a smaller film thickness after immersion was observed after ShAPE processing. The improved corrosion resistance of ShAPE processed alloy was attributed to grain refinement, homogenized distribution of second phases, and low residual strain in the matrix. Similarly, a tilted basal texture along the ShAPE processed direction contributed towards enhanced ductility and eliminated the tension-compression asymmetry.

Tailoring the corrosion behavior and mechanism of AZ31 magnesium alloys by different Ca contents for marine application

The microstructure of AZ31 magnesium alloy was modified by Ca addition. AZ31-Ca alloys with refined microstructure exhibited significantly enhanced corrosion resistance in artificial seawater. AZ31–0.5Ca showed the lowest corrosion rate of 0.716 ± 0.186 mm y−1, which was about 7.4 times lower than that of AZ31 alloy (5.326 ± 0.652 mm y−1). The dominant role in the reduced corrosion rates of AZ31-Ca alloys gradually changed from the compact corrosion products film containing Al2O3 and CaCO3 to the corrosion barriers consisting of net-like (Mg, Al)2Ca phases as the Ca content increased from 0.1 wt% to 1.5 wt%.

Mechanical Properties and Microstructure of AZ31 Magnesium Alloy Processed by Intermittent Ultrasonic-Assisted Equal Channel Angular Pressing

An intermittent ultrasonic-assisted equal channel angular pressing (IU-ECAP) technique for grain refinement is proposed in this study. AZ31 Mg alloy samples were divided into two groups (IU-ECAP and ECAP) and processed using four passes along route BC, and the effects of ultrasonic vibration on the mechanical properties and microstructure were examined. Mechanical testing revealed that IU-ECAP significantly reduced the extrusion force relative to that for ECAP, whereas the microhardness and ultimate tensile strength were strengthened. The maximum true ultimate tensile strength and microhardness of the IU-ECAPed specimens were achieved using ultrasonic vibration with an amplitude of 35 μm and intermittent time of 2 s. In addition, the microstructures were the most homogeneous for the smallest grain sizes. The IU-ECAPed specimens also possessed less high-angle grain boundaries because of the lower temperature of the IU-ECAP die. Texture analysis revealed that after the 4th pass, the texture of the IU-ECAPed specimens along the (0001) crystal plane exhibited maximum reduction; furthermore, the textures along the (0001), ( $$01\bar{1}0$$ ), and ( $$\bar{1}2\bar{1}0$$ ) crystal planes were scattered homogeneously. These findings may be related to ultrasonic-induced grain boundary rotation.

Improved microstructures of AZ31 magnesium alloy by semi-solid extrusion

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.

Effect of die parameters on the grain size, mechanical properties and fracture mechanism of extruded AZ31 magnesium alloys

The study was carried out to evaluate the effect of extrusion ratio and extrusion die angle on the mechanical properties and microstructure of AZ31 magnesium alloy at 300 °C extrusion temperature with three different extrusion ratio of 1.77, 2.68, 3.55 and die angles of 100, 150, 200. It was identified that microstructure was significantly refined for all extrusion ratios. The average size was decreased to the range of 4.1 μm–13.3 μm from 22.4 μm. By increasing extrusion ratio, it was observed that the tensile properties were considerably improved at room temperatures and tensile strength was reached to maximum 331 MPa after extrusion when initial measured value was 168.28 MPa. Significant grain refinement, enhanced mechanical strength and increase in microhardness values were observed with smaller die angles. It was observed that DRX mechanism is active and it supports the grain refinement. Dimples seen on the fractured surface were deeper that indicates the enhanced ductility of the material. Finally, among all the tests higher extrusion ratio with lower die angle gives better grain distribution in the microstructure and higher mechanical strength to the product.

Effects of ultrasonic vibration on performance and microstructure of AZ31 magnesium alloy under tensile deformation

Ultrasonic vibration can reduce the forming force, decrease the friction in the metal forming process and improve the surface quality of the workpiece effectively. Tensile tests of AZ31 magnesium alloy were carried out. The stress–strain relationship, fracture modes of tensile specimens, microstructure and microhardness under different vibration conditions were analyzed, in order to study the effects of the ultrasonic vibration on microstructure and performance of AZ31 magnesium alloy under tensile deformation. The results showed that the different reductions of the true stress appeared under various ultrasonic vibration conditions, and the maximum decreasing range was 4.76%. The maximum microhardness difference among the 3 nodes selected along the specimen was HV 10.9. The fracture modes, plasticity and microstructure of AZ31 magnesium alloy also were affected by amplitude and action time of the ultrasonic vibration. The softening effect and the hardening effect occurred simultaneously when the ultrasonic vibration was applied. When the ultrasonic amplitude was 4.6 μm with short action time, the plastic deformation was dominated by twins and the softening effect was dominant. However, the twinning could be inhibited and the hardening effect became dominant in the case of high ultrasonic energy.

Caracterización microestructural y modelización mediante elementos finitos de uniones soldadas de la aleación de Magnesio AZ31

En este artículo se ha investigado de qué manera la microestructura de las aleaciones de magnesio AZ31 se ve afectada por los ciclos térmicos que se producen durante los procesos de soldadura, tratando de modelizar mediante programas de elementos finitos los ciclos térmicos que se producen en estos materiales. Las muestras estudiadas han sido soldadas mediante soldadura TIG (Tungsten Inert Gas) y con diferentes materiales de aporte. En el estudio se ha empleado microscopía óptica para analizar la microestructura, microscopía electrónica de barrido y software de simulación. El estudio realizado indica por un lado que en este tipo de aleaciones los microconstituyentes más comunes son compuestos Al-Mn o Al-Mn-Mg, no observándose la presencia de la fase beta (Mg17Al12) a temperatura ambiente, por otro lado los modelos de simulación que se han obtenido indican que para las zonas que alcanzan temperaturas máximas del orden de 550 °C se produce la cristalización del material base y también sería el límite de las zona de disolución de los precipitados de composición Al-Mn o Al-Mn-Mg, que parecen actuar como inhibidores de la corrosión.

Microstructure of AZ31 Magnesium Alloy deformed by indentation-flattening compound deformation technology

Characteristic of indentation-flattening compound deformation technology (IFCDT) is discussed, and the parameters of IFCDT are defined. Performance of magnesium alloy AZ31 sheet deformed by IFCDT is researched. The effect of IFCDT coefficient, temperature and reduction ratio on the microstructure of magnesium alloy sheet is analyzed. The research results show that the volume fraction of the twin crystal decreases gradually and the average grain size increases with increasing of coefficient of IFCDT. With increase of the reduction ratio, the volume fraction of the twin crystal gradually increases, and the average grain size also increases. With increase of deformation temperature, the volume fraction of the twin crystal decreases gradually, and the twin crystal grain size increases.

Microstructural analysis and mechanical properties of AZ31 magnesium alloy prepared by alternate extrusion (AE)

One of the goals in the field of extrusion technology is to simplify the process and increase shear deformation in order to improve the grain refining capacity. This article innovatively tries to design a split punch structure and makes them alternate downward loading, so alternate extrusion (AE) method is proposed. Optical microscopy (OM), scanning electron microscope (SEM), and transmission electron microscopy (TEM) are employed to characterize the microstructure of AZ31 magnesium alloy during AE. Compared with the conventional extrusion (CE) under the same conditions, the microscopic experiment results show that the grain is more refined and the microstructure is more homogeneous. AE produces a large number of different direction dislocations and entangle with each other. The reasons for the above phenomenon are the plastic zone’s range of AE significantly increased. And between interface of double punch and die form a range of shear zone, which provides fully refined grain source power in the extrusion process. The tensile test results show that the mechanical properties of AE were better than CE, which is consistent with the results of our microscopic experiment results.

The influences of extrusion-shear process on microstructures evolution and mechanical properties of AZ31 magnesium alloy

Severe plastic deformation (SPD) technologies are difficult to be promoted to be industrialized, and the processes are complicated, and the costs are high. To promote industrial application of the SPD technology for magnesium alloy, a new successive SPD method has been explored which includes direct extrusion and two steps equal channel angular extrusion (ECAE) continuously. The processing technology is called extrusion-shear (ES) in this paper. The components of ES dies have been designed, manufactured and installed on extruder to manufacture the AZ31 magnesium alloy rods. Microstructures of AZ31 magnesium alloy processed by ES process have been observed and investigated. The texture evolution during ES process has also been studied. The results show that fine and uniform microstructures can be obtained by ES process. Basal texture (0002) has been weakened owing to shear deformation of ES process. Research results show that relationship between grain sizes and hardnesses is consistent with hall-petch law at 420 °C. ES process with low billet temperature could improve hardness obviously and enhance compression performance, and raise strengths. And there exits strong tension-compression asymmetry of AZ31 magnesium alloy fabricated by ES process. The results indicate that ES process can produce large plastic deformation and introduce ultra-fined grains in the AZ31 magnesium alloy.

Plasticity and microstructure of AZ31 magnesium alloy under coupling action of high pulsed magnetic field and external stress

As an h.c.p crystal structure with only a few limited slipping planes, the AZ31 magnesium alloy exhibits a bad plasticity in the presence of external stress. Due to its low density, advanced damping capacity and high ratio strength and rigidity, the magnesium alloy has gradually become the focused and potential structural and functional metallic material in the diverse fields of aerospace, aviation and vehicle transportation, electronic products, etc. Therefore, it is of great importance to improve the process ability of conventional magnetism alloy as AZ31. In the past decades many approaches have been proposed in order to improve the plastic deformation capability. Among these, the diverse physical fields are regarded as the effective methods to improve the comprehensive mechanical properties of metallic materials due to their peculiar heat, force and quantum effects together with the advantageous characteristics of low pollution and high efficiency. In the paper, on the basis of previous researches, a high pulsed magnetic field is introduced into the tensile test to study the influences of magnetic field on the plasticity and microstructure of AZ31 magnesium alloy in order to explore a novel way to enhance the plastic deformation capability of alloy. As for the current experiment, the tensile test of AZ31 magnesium alloy is carried out under the coupling action of high pulsed magnetic field and external stress. The test results are compared with those processed without magnetic field. Several advanced detection methods are utilized to investigate the microstructure including the electron back scattered diffraction, X-ray diffraction and transmission electron microscopy, etc. Besides, the first principle is utilized to calculate the magnetic properties of main precipitates (Mg17Al12).The experimental results show that the tensile strength and elongation of the 3 T sample are increased by 2.2% and 28.7% in comparison to those of the 0 T sample. It highlights that when the high pulsed magnetic field is introduced into the plastic deformation process, the plasticity of the magnesium alloy can be improved without reducing the tensile strength of the material. The action mechanism of magnetic field is analyzed in detail and attributed to the magnetoplasticity effect. The calculation results on the basis of first principle show that the (Mg17Al12) phase is paramagnetic, which is helpful for performing the effect of magnetic field. The magnetic field enhances the flexibility of the dislocation movement and facilitates the proliferation of the dislocation. The dislocation and stress concentrating at the grain boundaries accelerate the formation of recrystallization, which is of great importance to the sub-grain generation and grain refinement that is beneficial to exhibiting the fine grain strengthening and enhancing the strength and toughness of alloy. Meanwhile, during the peculiar tensile process, the magnetic field induces the grain rotation. The newborn fine grains along the non-basal face weaken the (0001) basal texture of magnesium alloy. The characteristic of the texture structure is helpful for improving the plastic deformation capacity of AZ31 alloy. The plastic deformation under high magnetic field is regarded as an advanced way to improve the plasticities of similar nonmagnetic metallic materials such as aluminum, titanium and copper alloys and their composites.

The effect of Gd element and solution treatment on the microstructure of AZ31 magnesium alloy and its kinetic model

The influence of Gd element and solution treatment on the microstructure of AZ31 alloy was investigated in this paper. The microstructure and phase composition were characterized by OM, SEM, EDS and XRD. The results indicate that Mg17Al12 eutectic phase, scattered along the grain boundary, is suppressed effectively with Gd addition and the acicular Al2Gd superlattice with lamellar distribution is formed. Furthermore, the grain size of AZ31 alloy is also refined with Gd addition. In the subsequent process of solution, the migration and growth of Al2Gd phase conforms to Ostwald Ripening Theory. The morphology of Al2Gd phase becomes granular and scatterd in matrix uniformly after solution for 16 h at 813 K.

Comparation about Refining Efficiency to Microstructure of AZ31 Magnesium Alloy for Sr Master Alloys

In the present work, the influence of Al-Sr and Mg-Sr master alloys on the as-cast microstructure of the AZ31 magnesium alloy was investigated,and the refinement efficiencies of both master alloys were also analyzed and compared. The research results indicate that both the Al-Sr and Mg-Sr master alloys have obvious refinement effect on the as-cast microstructure of the AZ31 magnesium alloy, and the refinement efficiency of the Mg-Sr master alloys was better than that of the Al-Sr master alloys. The mechanisms for the differences of grain refinement efficiency between Al-Sr and Mg-Sr master alloys on the AZ31 magnesium alloys were also discussed.

Effect of electropulsing rolling on mechanical properties and microstructure of AZ31 magnesium alloy

Electropulsing rolling (ER) and warm rolling (WR) processes were performed to roll AZ31 magnesium alloy sheets. Mechanical properties, microstructure and texture evolution of these specimens were investigated after rolling. The results indicate that electropulsing accelerates the recrystallization of AZ31 alloy sheets during hot rolling. After electropulsing rolling at a relatively low temperature, the microstructure of the sample shows fine equiaxed recrystallized grains with a lower density of dislocations and precipitates. In contrast, the microstructure of the sample after warm rolling shows elongated grain, numerous deformed twins, and a high density of dislocation and precipitates. Electropulsing rolling helps weaken the basal fiber texture. Although both the alloy sheets (ER and WR) have typical basal fiber texture, the maximum pole intensity of basal in ER sample is weaker. ER sheet has higher yield strength and elongation compared to WR sheet. As a promising technique, electropulsing rolling can be used to improve the microstructure and mechanical properties of materials.

Microstructure of AZ31 magnesium alloy produced by continuous variable cross-section direct extrusion (CVCDE)

In order to study the effect of a new Severe Plastic Deformation (SPD) technique-continuous variable cross-section direct extrusion (CVCDE) on improving the mechanical properties of magnesium alloy, electronic backscattered diffraction (EBSD) was employed to investigate the microstructure and texture of CVCDEed AZ31 magnesium alloy. Compared with conventional extrusion (CE), CVCDE can increase the accumulated strain without changing the total extrusion ratio during extrusion process. Under the effect of CVCDE, coarse grains can be further sheared up to refined grains and the number of dynamic recrystallization grains increases. At the same time, this method can significantly weaken basal plane texture and improve tensile strength and elongation of CVCDEed product, which provides an effective way to produce excellent performance magnesium alloys.

3D finite element modeling of grains refinement for magnesium alloys by extrusion-shear and experimental verification

To explore the deformation mechanisms of a new composite extrusion including extrusion and successive shear subsequently which is shorten ES, Three dimensional finite element modeling of grain refinements for magnesium alloys by ES process has been researched. The ES die have been designed and manufactured and installed to the horizontal extruder. Finite element software DEFORMTM-3D to investigate the plastic deformation behaviors of magnesium alloy during extrusion-shear has been employed. The extrusion loads and temperatures distribution of billets and maximum extrusion forces have been obtained from simulation results. From the simulation results it is clear that evolutions of extrusion loads curve and effective stresses and temperatures can be divided into three stages. ES process has been applied to fabricate AZ31 magnesium alloy rod at preheat temperature of 420oC with extrusion speed of 20 mm/s. The results proved that the ES process is a formality method for magnesium suitable for large scale industrial application. The microstructures of AZ31 magnesium alloy along the longitudinal section of rods have been sampled and examined and observed. Fine grained microstructures can be observed throughout longitudinal section of extruded rod. The researches results show that ES process would cause severe plastic deformation and improve the dynamic recrystallization of AZ31 magnesium alloy. The simulation results and calculated Zener-Hollomon parameters showed that the grains of magnesium would be refined gradually during ES process.

Effect of LPC on the Corrosion Behavior of AZ81 Magnesium Alloy

The corrosion behavior of AZ81 magnesium alloy with the LPC addition has been investigated in this paper. The results show that with the addition of 1-5% LPC, the microstructure of AZ81 magnesium alloy is remarkably refined, and the spotted, high-melting point phase Al-RE intermetallic compounds is found in the alloy. The corrosion behavior of AZ81 alloy decreases firstly and then increases sharply with the increase of LPC addition. When the content of LPC is 2.5%, AZ81 magnesium alloy shows the lowest corrosion rate. The corrosion rates in 3.5%NaCl solution are always higher than those in 0.5%NaCl solution. The corrosion products from the surface are mainly composed of Mg (OH) 2 compositions.

Effects of an overlapping multi-pass friction stir process and rapid cooling on the mechanical properties and microstructure of AZ31 magnesium alloy

Applications for magnesium as the lightest structural metal are increasing; however, its low ductility at room temperature could be considered a limitation. The friction stir process (FSP) is a solid state process that can overcome this limitation by producing a fine-grained material and uniform texture. This study used overlapping passes FSP to create a fine-grained area on the surface of AZ31 magnesium alloy. Rapid cooling was employed during the process to eliminate the thermal effects of successive passes. Two different modes of overlap were created. In the first mode, the surface of the sample was FSPed overlapping in one direction. In the second mode, the first overlapped surface of the sample was overlapped again in a direction perpendicular to the primary process. The results showed that mechanical strength in the process direction increased for both modes. Elongation was greater for the first mode than that of the raw material and, for the second mode, was less than for the raw material. In the direction perpendicular to the process, both the mechanical strength and ductility of the material were less than those of the raw material. The particle distribution in the second mode was more uniform than that for the first mode.

Microstructural Evolution and Mechanical Properties of AZ31 Magnesium Alloy Prepared by Casting-solid Extrusion Forging During Partial Remelting

Abstract The casting-solid extrusion forging plus semi-solid partial remelting route is used to improve the properties of AZ31 magnesium alloy products. The effect of remelting temperature and holding time on the microstructure of AZ31 magnesium alloy is studied. Furthermore, the properties of AZ31 magnesium alloy components produced by the casting-solid extrusion forging plus partial remelting route are examined. The results show that the AZ31 components have very good smooth surface and are formed completely. The increases in holding time and remelting temperature result in the formation of spheroidal grains surrounded by liquid phases. The best combination of properties of thixoforged alloy is 290 MPa of tensile strength, 220 MPa of yield strength and 10% of percentage elongation.