基于Marc的ECAP-FE累積塑性變形工藝數(shù)值模擬研究
發(fā)布時間：2019-01-25 19:08
【摘要】：鎂合金被譽為21世紀可持續(xù)發(fā)展的“綠色材料”,也是目前最輕的金屬結(jié)構(gòu)材料,具有很高的比強度,主要應(yīng)用于醫(yī)學、3C電子產(chǎn)品、汽車、航空航天等各個領(lǐng)域,已然成為世界各國關(guān)注和研究的焦點。由于鎂合金具有密排六方結(jié)構(gòu)的特點,在室溫變形條件下獨立的滑移系較少,因此室溫下塑性差,變形加工困難,需要采用大塑性變形復合工藝才能有效的細化鎂合金晶粒,以提高鎂合金的塑性,從而改善其加工性能。以促進變形鎂合金產(chǎn)品在各個領(lǐng)域的廣泛應(yīng)用。由于傳統(tǒng)的鎂合金擠壓棒材的變形能力和強韌性差,采用等通道轉(zhuǎn)角擠壓大塑性變形技術(shù)(ECAP),即由兩個相交的等徑通道組成的模具并通過純剪切方式實現(xiàn)塊體金屬材料大塑性變形的成形工藝,它能夠有效的制備超細晶結(jié)構(gòu)材料,但是,需要多道次等通道轉(zhuǎn)角擠壓成形才能獲得組織均勻的高性能材料,并且在多道次擠壓過程中還容易出現(xiàn)開裂現(xiàn)象,因此,這種大塑性變形工藝難以進行工業(yè)化推廣。本文基于等通道轉(zhuǎn)角擠壓工藝的缺陷,提出并設(shè)計了等通道轉(zhuǎn)角擠壓與正擠壓相復合的累積變形工藝(以下簡稱ECAP-FE),即在等通道轉(zhuǎn)角擠壓型腔后直接連接一個具有一定擠壓比的正擠壓芯模,由此形成一個集多種變形工藝于一體的連續(xù)擠壓型腔,從而實現(xiàn)對材料的累積塑性變形。由此找到一種提高鎂合金塑性的新途徑。本文首先采用二次開發(fā)技術(shù)在MSC.Marc軟件中建立了AZ31鎂合金的材料模型,然后構(gòu)建了AZ31鎂合金微觀組織預測系統(tǒng)的程序開發(fā)流程圖,并利用FORTRAN語言對微觀組織模型進行編程,成功的預測了擠壓過程中AZ31鎂合金的晶粒尺寸和動態(tài)再結(jié)晶體積分數(shù)的變化過程。將構(gòu)建成功的AZ31鎂合金的ECAP-FE擠壓過程有限元分析模型進行數(shù)值模擬。最后對AZ31鎂合金在ECAP-FE擠壓模擬過程中的擠壓力、等效應(yīng)力場、等效應(yīng)變場、等效應(yīng)變速率進行有限元分析。模擬結(jié)果表明:與單一的ECAP擠壓工藝相比,ECAP-FE復合擠壓變形工藝能有效的提高材料的變形量,使材料產(chǎn)生累積變形,細化晶粒;并且,ECAP-FE復合擠壓變形工藝所獲得的平均等效應(yīng)變提高了約2倍,等效不均勻系數(shù)有很大幅度的下降,且等效應(yīng)變呈軸對稱分布,因此ECAP-FE能實現(xiàn)較高的累積塑性變形;而且,在ECAP-FE復合擠壓工藝中,正擠壓的模面能夠為ECAP擠壓過程提供有效背壓,減小剪切帶面積,使之更接近理想的簡單切變;使得經(jīng)ECAP-FE擠壓后的最大等效應(yīng)變速率為0.9916,最大等效應(yīng)變速率顯著提高。由此表明ECAP-FE復合累積塑性變形工藝可獲取更加細小、均勻的晶粒組織。此結(jié)果為ECAP-FE復合擠壓工藝的進一步深入研究提供了理論依據(jù)。
[Abstract]:Magnesium alloys are praised as "green materials" for sustainable development in the 21st century. They are also the lightest metal structural materials at present. They have high specific strength and are mainly used in medicine, 3C electronic products, automobiles, aerospace and other fields. Has become the focus of attention and research around the world. Because magnesium alloy has the characteristic of dense hexagonal structure and there are few independent slip systems under room temperature deformation, it is difficult to deform and deform at room temperature, so it is necessary to use large plastic deformation composite process to refine magnesium alloy grain effectively. In order to improve the plasticity of magnesium alloys and improve their processing properties. In order to promote the wide application of wrought magnesium alloy products in various fields. Due to the poor deformation ability and strength and toughness of the traditional magnesium alloy extruded bar, (ECAP), is used to extrude large plastic deformation technology at equal channel angle. That is, the mould composed of two intersecting equal channels and the forming process of large plastic deformation of bulk metal material by pure shear, it can effectively prepare ultrafine crystal structure material, but, High performance materials with uniform microstructure can be obtained by multi-pass secondary channel angular extrusion forming, and cracking is easy to occur in multi-pass extrusion process. Therefore, this kind of large plastic deformation process is difficult to be popularized in industry. Based on the defects of the equal channel angular extrusion process, the cumulative deformation process of equal channel angular extrusion and forward extrusion (hereinafter referred to as ECAP-FE) is proposed and designed in this paper. That is, a positive extrusion core die with a certain extrusion ratio is connected directly behind the equal channel angular extrusion cavity, and a continuous extrusion cavity with multiple deformation processes is formed, thus the cumulative plastic deformation of the material is realized. Therefore, a new way to improve the plasticity of magnesium alloy is found. In this paper, the material model of AZ31 magnesium alloy is established by using secondary development technology in MSC.Marc software, then the program development flow chart of AZ31 magnesium alloy microstructure prediction system is constructed, and the microstructure model of AZ31 magnesium alloy is programmed by FORTRAN language. The change of grain size and dynamic recrystallization integral number of AZ31 magnesium alloy during extrusion was successfully predicted. The finite element analysis model of ECAP-FE extrusion process of AZ31 magnesium alloy was numerically simulated. Finally, the extrusion force field, equivalent strain rate and equivalent strain field of AZ31 magnesium alloy during ECAP-FE extrusion simulation are analyzed by finite element method. The simulation results show that compared with the single ECAP extrusion process, the ECAP-FE composite extrusion process can effectively increase the amount of deformation of the material, make the material produce cumulative deformation and refine the grain. Moreover, the average equivalent strain obtained by ECAP-FE composite extrusion process has increased by about 2 times, and the equivalent inhomogeneity coefficient has been greatly reduced, and the equivalent strain has been distributed symmetrically, so ECAP-FE can achieve higher cumulative plastic deformation. Moreover, in the process of ECAP-FE composite extrusion, the die face of forward extrusion can provide effective back pressure for ECAP extrusion process, reduce the area of shear band, and make it closer to the ideal simple shear. The maximum equivalent strain rate after ECAP-FE extrusion is 0.9916, and the maximum equivalent strain rate increases significantly. It is shown that ECAP-FE composite cumulative plastic deformation process can obtain more fine and uniform grain structure. The results provide a theoretical basis for the further study of ECAP-FE composite extrusion process.
【學位授予單位】：哈爾濱理工大學
【學位級別】：碩士
【學位授予年份】：2016
【分類號】：TG379
本文編號：2415092
[Abstract]:Magnesium alloys are praised as "green materials" for sustainable development in the 21st century. They are also the lightest metal structural materials at present. They have high specific strength and are mainly used in medicine, 3C electronic products, automobiles, aerospace and other fields. Has become the focus of attention and research around the world. Because magnesium alloy has the characteristic of dense hexagonal structure and there are few independent slip systems under room temperature deformation, it is difficult to deform and deform at room temperature, so it is necessary to use large plastic deformation composite process to refine magnesium alloy grain effectively. In order to improve the plasticity of magnesium alloys and improve their processing properties. In order to promote the wide application of wrought magnesium alloy products in various fields. Due to the poor deformation ability and strength and toughness of the traditional magnesium alloy extruded bar, (ECAP), is used to extrude large plastic deformation technology at equal channel angle. That is, the mould composed of two intersecting equal channels and the forming process of large plastic deformation of bulk metal material by pure shear, it can effectively prepare ultrafine crystal structure material, but, High performance materials with uniform microstructure can be obtained by multi-pass secondary channel angular extrusion forming, and cracking is easy to occur in multi-pass extrusion process. Therefore, this kind of large plastic deformation process is difficult to be popularized in industry. Based on the defects of the equal channel angular extrusion process, the cumulative deformation process of equal channel angular extrusion and forward extrusion (hereinafter referred to as ECAP-FE) is proposed and designed in this paper. That is, a positive extrusion core die with a certain extrusion ratio is connected directly behind the equal channel angular extrusion cavity, and a continuous extrusion cavity with multiple deformation processes is formed, thus the cumulative plastic deformation of the material is realized. Therefore, a new way to improve the plasticity of magnesium alloy is found. In this paper, the material model of AZ31 magnesium alloy is established by using secondary development technology in MSC.Marc software, then the program development flow chart of AZ31 magnesium alloy microstructure prediction system is constructed, and the microstructure model of AZ31 magnesium alloy is programmed by FORTRAN language. The change of grain size and dynamic recrystallization integral number of AZ31 magnesium alloy during extrusion was successfully predicted. The finite element analysis model of ECAP-FE extrusion process of AZ31 magnesium alloy was numerically simulated. Finally, the extrusion force field, equivalent strain rate and equivalent strain field of AZ31 magnesium alloy during ECAP-FE extrusion simulation are analyzed by finite element method. The simulation results show that compared with the single ECAP extrusion process, the ECAP-FE composite extrusion process can effectively increase the amount of deformation of the material, make the material produce cumulative deformation and refine the grain. Moreover, the average equivalent strain obtained by ECAP-FE composite extrusion process has increased by about 2 times, and the equivalent inhomogeneity coefficient has been greatly reduced, and the equivalent strain has been distributed symmetrically, so ECAP-FE can achieve higher cumulative plastic deformation. Moreover, in the process of ECAP-FE composite extrusion, the die face of forward extrusion can provide effective back pressure for ECAP extrusion process, reduce the area of shear band, and make it closer to the ideal simple shear. The maximum equivalent strain rate after ECAP-FE extrusion is 0.9916, and the maximum equivalent strain rate increases significantly. It is shown that ECAP-FE composite cumulative plastic deformation process can obtain more fine and uniform grain structure. The results provide a theoretical basis for the further study of ECAP-FE composite extrusion process.
【學位授予單位】：哈爾濱理工大學
【學位級別】：碩士
【學位授予年份】：2016
【分類號】：TG379
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