Continuous Variable Cross-section Direct Extrusion Research Articles

Effect of directionality of AZ31 magnesium alloy sheets produced by continuous variable cross-section direct extrusion on corrosion behavior

Effect of directionality of AZ31 magnesium alloy sheets produced by continuous variable cross-section direct extrusion on corrosion behavior

Microstructure and mechanical properties of ZM6 magnesium alloy after continuous variable cross-section direct extrusion

Microstructure and mechanical properties of ZM6 magnesium alloy after continuous variable cross-section direct extrusion

Corrosion Behavior of AZ31 Magnesium Alloy Produced by Continuous Variable Cross Section Direct Extrusion

In order to study the corrosion behavior of magnesium alloys of high performance in the simulated seawater by continuous variable cross section direct extrusion (CVCDE), an electrochemical method and weight loss method were used to study the difference between AZ31 magnesium alloys produced by CVCDE with different numbers of interim dies to examine the electrochemical corrosion behavior and corrosion rate at 3.5 wt.% NaCl solution in this paper. Scanning electron microscopy and x-ray diffraction were used to analyze the morphology of corrosion surfaces and the composition of the corrosion products of samples soaked for different times. The results show that after CVCDE with different numbers of interim dies, the size of the microstructure is refined gradually, and the grain orientation is also different; with the increase in the number of interim dies, the thermodynamic corrosion tendencies are different, and the corrosion resistance of samples extruded by conventional extrusion is relatively good; the charge transfer and material transfer process are the two main factors affecting the corrosion rate, which determines the direction of the electrochemical reaction; the corrosion form of the sample extruded by CVCDE is the local corrosion which is the filiform corrosion and pitting corrosion, and the corrosion product is mainly water-insoluble Mg(OH)2.

Microstructural Analysis and Texture Evolution of the CVCEDed AZ31 Magnesium Alloy by Hot Rolling

Grain refinement is one of the important methods to improve the performance of magnesium alloy sheets. This paper attempts to prepare the billets of AZ31 magnesium alloy sheets by continuous variable cross-section direct extrusion (CVCDE) and then prepare sheets by rolling. The results show that the average grain size of the sheets rolled from extruded products by CVCDE with 2 interim dies reduced by 30% and the tensile strength increased by 12.6% compared with the sheets rolled from extruded products by traditional extrusion (CE), which is related to the dislocation multiplication in the corresponding conditions. The high dislocation density hinders the plastic deformation of the material, which is one of the internal factors that cause the increase in the strength of the material and the decrease in the plasticity. In addition, the basal surface of a lot of grains of the sheets rolled from extruded products by CVCDE with 2 interim dies is parallel to the RD-TD plane and the strength of texture is high. Meanwhile, the value of average Schmid factor of the sheets rolled from extruded products by CVCDE with 2 interim dies along the rolling direction is lowest, which result in lower plasticity. The above research provides a new idea for the development of high-performance magnesium alloy sheets.

Microstructural Characteristics of AZ31 Magnesium Alloy Processed by Continuous Variable Cross-Section Direct Extrusion (CVCDE). Part 1: Texture Evolution

Extrusion products with ideal microstructure and mechanical properties can be obtained by precise design of the mold cavity structure. In this study, two interim dies were taken as a sample to investigate the texture of typical locations of AZ31 magnesium alloy produced by continuous variable cross-section direct extrusion (CVCDE). The results show that grains were refined significantly after the material passed through the continuous variable mold cavity. Stronger extrusion fiber texture formed during the CVCDE process, and the texture type of the extrusion product transformed from {0001}〈10–10〉 deformation texture to a mixture of {0001}〈10-10〉 deformation texture and {0001}〈11–20〉 recrystallization texture. During the extrusion process, the c-axis of the majority of grains deflected under the action of external forces and tended to become parallel to the direction of the external forces. Therefore, the value of the Schmid factor, which represents the grain orientation, became smaller and the grains were in hard orientation, making further slip difficult.

Microstructural Characteristics of AZ31 Magnesium Alloy Processed by Continuous Variable Cross-Section Direct Extrusion (CVCDE). Part 2: Dynamic Recrystallization

Through the precise design of the mold cavity structure, the ideal microstructure and mechanical property of the extrusion product can be obtained. In this article, the two interim dies were taken as a sample to study the microstructure of typical locations of AZ31 magnesium alloy produced by continuous variable cross-section direct extrusion (CVCDE). The results showed that the grains were refined significantly and became more homogeneous after the material passed through the continuous variable mold cavity. By contrast of different locations of the extrusion product, the dynamic recrystallization was sufficient and the proportion of recrystallization grains was the largest at the outlet position of the mold die.

Properties of Rolled AZ31 Magnesium Alloy Sheet Fabricated by Continuous Variable Cross-Section Direct Extrusion

Rolling is currently a widely used method for manufacturing and processing high-performance magnesium alloy sheets and has received widespread attention in recent years. Here, we combined continuous variable cross-section direct extrusion (CVCDE) and rolling processes. The microstructure and mechanical properties of the resulting sheets rolled at different temperatures from CVCDE extrudate were investigated by optical microscopy, scanning electron microscope, transmission electron microscopy and electron backscatter diffraction. The results showed that a fine-grained microstructure was present with an average grain size of 3.62 μm in sheets rolled from CVCDE extrudate at 623 K. Dynamic recrystallization and a large strain were induced by the multi-pass rolling, which resulted in grain refinement. In the 573-673 K range, the yield strength, tensile strength and elongation initially increased and then declined as the CVCDE temperature increased. The above results provide an important scientific basis of processing, manufacturing and the active control on microstructure and property for high-performance magnesium alloy sheet.

Effect of different temperatures on deformation characteristics of AZ31 magnesium alloy by continuous variable cross-section direct extrusion

This paper based on the research of the different temperatures of AZ31 magnesium alloy by continuous variable cross-section direct extrusion (CVCDE) studied the effect of forming temperature on the deformation characteristics of magnesium alloy by CVCDE. It was found that the average size of grains and the proportion of large angle grain boundaries in microstructure increased obviously with the increase of forming temperature, which showed dynamic recrystallization has been relatively adequate. Because the dislocation density inside the grains was higher and the texture was weakened obviously at 623 K by compared with other temperatures, the yield strength and elongation increased at first and then decreased with the increase of temperature. This paper reveals the deformation mechanism of AZ31 magnesium alloy by CVCDE, which can provide scientific guidance for the development of magnesium alloy extrusion products with high property.

Microstructural characteristics and deformation of magnesium alloy AZ31 produced by continuous variable cross-section direct extrusion

Magnesium (Mg) alloy AZ31 was produced by continuous variable cross-section direct extrusion (CVCDE) to study its deformation behavior. Metallographic microscopy (OM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) were used to observe the variations in microstructure and fracture morphology of Mg alloy AZ31 as a function of processing methods. The results reveal that grains of Mg alloy AZ31 were refined and their microstructure was homogenized by CVCDE. The recrystallization in Mg alloy AZ31 produced by CVCDE with 2 interim dies was more complete than that produced by conventional extrusion (CE) and CVCDE with 1 interim die, and the grains were finer and more uniform. Plasticity of the AZ31 alloy was improved. Fracture mode was evolved from a combination of ductility and brittleness to a sole ductile form. In summary, a CVCDE mold structure with 2 interim dies can improve microstructure, plasticity, and toughness of Mg alloy AZ31.

Effects of processing parameters on the extrusion by continuous variable cross-section direct extrusion with 7A09 aluminium alloy

In order to study the effects of processing parameters on the continuous variable cross-section direct extrusion (CVCDE), taking 7A09 aluminium alloy for example, the extrusion speed and forming temperature and the friction factor as key processing parameters are applied to research by finite element (FE) simulation. The research result showed that the extrusion speed had a significant influence on the maximum temperature of the billet, at the same time, both decreasing the friction factor and increasing forming temperature within a certain range were beneficial to reduce extrusion load. Both forming temperature and the extrusion speed were inversely linked to extrusion load, but the friction factor was directly proportional to extrusion load. Forming temperature had a far more important influence on extrusion load by comparison: when forming temperature increased from 380[Formula: see text] to 430[Formula: see text]C, the peak value of extrusion load decreased by 25.6% and the flow uniformity of extruded product got improved. The process window based on both the press limit and surface defects limit was established and the most reasonable forming temperature was 405[Formula: see text]C under this process condition, which provided theoretical basis for formulation process of 7A09 aluminium alloy on the CVCDE extrusion.

Investigation of 7A09 aluminum alloy prepared by continuous variable cross-section direct extrusion (CVCDE)

Preparation-forming is a common method to get high-performance alloy products, but lots of shortcomings exist in this method, such as complex and long process, high costs, and so on. As a new severe plastic deformation technology, continuous variable cross-section direct extrusion (CVCDE) is used to solve these problems. Taking 7A09 aluminum alloy, for example, the research result of CVCDE process shows that actual material flow distance is longer than conventional extrusion, and the axial stress on product surface in the die orifice is also significantly decreased. At the same time, the material flows through die cavity sequentially and suffers “upsetting-extrusion-upsetting” continuous loading, which will result in a severe deformation. By analysis of the microstructure and mechanical properties of 7A09 aluminum alloy was obtained under different conditions, it can be known that the grains become smaller and more round, and the uniformity gets also improved after CVCDE. Compared with conventional extrusion, the grain refinement of CVCDE with one and two interim dies increased by 22.4 and 41.5 %, respectively, and tensile strength and elongation also increase. To sum up, CVCDE with high efficiency, low consumption, short process, and other unique advantages in obtaining high-performance alloy products will be certainly raised wide concern.

Effect of local strains on the texture and mechanical properties of AZ31 magnesium alloy produced by continuous variable cross-section direct extrusion (CVCDE)

Abstract Three different mold structures were designed by changing the parameters of mold cavity to study the effect of local strains on the texture and mechanical properties of AZ31 magnesium alloy produced by continuous variable cross-section direct extrusion (CVCDE) with 2 interim dies. Microstructure and texture evolution of AZ31 magnesium alloy after CVCDE were studied by electron backscatter diffraction (EBSD). Mechanical properties were determined by uniaxial tensile tests along extrusion direction (ED) at room temperature. Due to the differences of local strains among the three schemes, the microstructure of Scheme 1 was the most uniform and the average grain size of Scheme 1 was the smallest. Meanwhile, tensile strength and elongation of Scheme 1 were the highest. Different textures had been formed in the three schemes. Lots of extension twins {10–12} (86° ) occurred in the products of the three schemes. The main deformation modes of Scheme 1 and Scheme 2 were slip and twinning. However, slip was dominant in Scheme 3. The deformation modes provided an essential basic for the design of CVCDE mold structure with more interim dies.

Investigation of microstructure characteristics of the CVCDEed AZ31 magnesium alloy

In this paper, the mold structure of continuous variable cross-section direct extrusion (CVCDE) was changed by adding interim dies, and the microstructure characteristics of AZ31 magnesium alloy produced by CVCDE with three interim dies were investigated by electron backscattered diffraction (EBSD) and transmission electron microscope (TEM) to study their effects on the mechanical properties. Studies found that the technique of CVCDE with 3 interim dies could effectively refine grains, change texture type and weaken texture intensity, which greatly improved the ductility of AZ31 magnesium alloy. However, compared with the strengthening effect of grain refinement, the weak basal texture and basal slip played a major role on the reduced yield strength. At the same time, the amount of twins reduced and a narrow banded type of extension twin 101¯2 (86.3°112¯0) occurred after CVCDE with 3 interim dies, which were different from those in original extruded bar.

Effect of Accumulative Strain on Grain Refinement and Strengthening of ZM6 Magnesium Alloy During Continuous Variable Cross-Section Direct Extrusion

In order to study the influence of die combination on continuous variable cross-section direct extrusion (CVCDE) in the extrusion process, the accumulative strain formula is derived, and it can be known that the extrusion ratio of various stages directly determines the size of corresponding stage strain by formula. In this paper, as an example of the two interim dies, three die combinations of different angles and extrusion ratio are designed. Aviation magnesium alloy ZM6 is studied, and the results show that dynamic recrystallization is even more complete when continuous shear deformation occurs, so that the refinement and homogenization of microstructure are obtained. By the use of different die combinations, the accumulative strain increases under the conditions of same total extrusion ratio. Thus, the refined crystalline strengthening effect of extrusion deformation can be further analyzed. Due to the dead-zone defects, the actual accumulative strain decreases significantly and the effect of microstructure and performance improvements also decreases with it. Therefore, the optimal design of die combination is the key to the process and product of CVCDE, which provides a scientific basis for the development of severe plastic deformation.

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.