本文選題：Mg-13Gd-4Y-2Zn-0.5Zr稀土鎂合金　切入點：均勻性　出處：《中北大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：作為大型設(shè)備的核心部件,大型構(gòu)件工況特殊,受力復(fù)雜,質(zhì)量要求嚴格,對力學(xué)性能提出了更高的要求。在各種成形方法中,塑性變形工藝能夠有效提升工件力學(xué)性能,而循環(huán)鐓擠作為一種大塑性變形工藝,具有顯著改善工件組織均勻性和提升力學(xué)性能的優(yōu)點。對于性能要求較高的大型構(gòu)件,使用循環(huán)鐓擠的方法進行預(yù)成形改性,使其在終成形前達到細化晶粒尺寸,提升力學(xué)性能的目的。本文以成形Mg-13Gd-4Y-2Zn-0.5Zr稀土鎂合金大型構(gòu)件為背景,對該合金多道次循環(huán)鐓擠進行實驗研究,重點研究了多道次循環(huán)鐓擠工藝對應(yīng)變量,力學(xué)性能,微觀組織和均勻性的影響。研究了多道次循環(huán)鐓擠對Mg-13Gd-4Y-2Zn-0.5Zr稀土鎂合金室溫力學(xué)性能的影響。結(jié)果表明,隨著循環(huán)鐓擠變形道次的增加,合金的抗拉強度和屈服強度不斷增強,延伸率出現(xiàn)先上升,后下降,再上升的變化趨勢,第二相的析出是延伸率下降的主要誘因,合金4道次變形后抗拉強度和延伸率達到了364MPa和10.32%,屈服強度和抗拉強度分別為鑄態(tài)時的1.68倍和2.06倍。另一方面,隨著循環(huán)鐓擠變形道次的增加,合金的硬度值逐漸增大,1-3道次變形過程中,合金不同部位的硬度值曲線呈現(xiàn)出明顯的發(fā)散狀態(tài),不均勻分布現(xiàn)象顯著,4道次變形后硬度值曲線開始集束且基本與平均硬度值曲線相重合;力學(xué)性能均勻性獲得顯著提高。通過研究Mg-13Gd-4Y-2Zn-0.5Zr稀土鎂合金循環(huán)鐓擠變形后的微觀組織,發(fā)現(xiàn)循環(huán)鐓擠變形對合金具有強烈的細化作用,隨著變形道次的增加,合金的細化效率逐漸降低,平均晶粒尺寸由50.6um細化到7.5um,晶粒尺寸數(shù)值跨度從1道次的27-38um,降低至4道次的7.2-9.8um,組織均勻性獲得顯著提高。同時,擠壓溫度的降低造成了第二相的大量析出,阻礙了位錯運動的進行。在細晶強化和第二相強化的共同作用下,合金的力學(xué)性能得到顯著提高。使用有限元模擬軟件對多道次循環(huán)鐓擠進行了模擬,揭示了變形過程中不同場變量的分布情況,結(jié)果顯示,等效應(yīng)力場的分布從縮頸區(qū)向頂部和底部逐級遞減。在變形初期,工件應(yīng)變由內(nèi)而外存在明顯的應(yīng)變梯度,其中表面應(yīng)變最大,為7.3,底部應(yīng)變最小,為1.21,應(yīng)變差值達到了6.09,應(yīng)變分布不均勻,隨著變形道次的增加,在累積應(yīng)變的作用下,工件的大應(yīng)變區(qū)域和應(yīng)變均勻性區(qū)域在擴大;4道次變形后,工件不同部位的等效應(yīng)變值范圍達到了10.5-12.5,應(yīng)變不均勻參數(shù)C值由2.481降低到0.151,應(yīng)變均勻性獲得顯著提升。5-6道次變形后,工件應(yīng)變均勻性沒有進一步改善。通過本文的研究,掌握了循環(huán)鐓擠工藝變形規(guī)律,確立了Mg-13Gd-4Y-2Zn-0.5Zr稀土鎂合金循環(huán)鐓擠的最佳變形道次,為該工藝的推廣和應(yīng)用奠定了基礎(chǔ),對豐富大型構(gòu)件預(yù)成形理論與和實踐提供了指導(dǎo)和參考意義。
[Abstract]:As the core components of large equipment, large components have special working conditions, complex forces and strict quality requirements, which put forward higher requirements for mechanical properties. Among all kinds of forming methods, plastic deformation technology can effectively improve the mechanical properties of workpieces. As a large plastic deformation process, cyclic upsetting extrusion has the advantages of improving the structure uniformity and improving the mechanical properties of the workpiece. In order to improve the mechanical properties of large components with high performance, the cyclic upsetting extrusion method is used to preform the large components. The purpose of refining grain size and improving mechanical properties is achieved before the final forming. In this paper, the multi-pass cyclic upsetting of Mg-13Gd-4Y-2Zn-0.5Zr magnesium alloy is studied in this paper. The effects of relative variables, mechanical properties, microstructure and homogeneity of multi-pass cyclic upsetting extrusion on the mechanical properties of Mg-13Gd-4Y-2Zn-0.5Zr rare earth magnesium alloys at room temperature were studied. With the increase of cyclic upsetting deformation pass, the tensile strength and yield strength of the alloy increase continuously, and the elongation increases first, then decreases, and then rises. The precipitation of the second phase is the main cause of the decrease of elongation. The tensile strength and elongation of the alloy reached 364MPa and 10.32MPa after 4 times of deformation, and the yield strength and tensile strength were 1.68 and 2.06 times of those of the as-cast alloy, respectively. On the other hand, with the increase of cyclic upsetting deformation pass, the tensile strength and elongation of the alloy reached 364MPa and 10.32MPa, respectively. When the hardness value of the alloy increases gradually, the hardness curves of different parts of the alloy show a distinct divergence state during the process of 1-3 pass deformation. After 4 times of deformation, the hardness curve began to gather and basically coincided with the average hardness curve, and the mechanical property uniformity was improved significantly. The microstructure of Mg-13Gd-4Y-2Zn-0.5Zr rare earth magnesium alloy after cyclic upsetting and extrusion was studied. It is found that cyclic upsetting deformation has a strong refining effect on the alloy, and with the increase of deformation pass, the refining efficiency of the alloy decreases gradually. The average grain size was refined from 50.6um to 7.5um. the numerical span of grain size decreased from 27-38um-1 to 7.2-9.8um. at the same time, the decrease of extrusion temperature resulted in a large amount of precipitation of the second phase. The mechanical properties of the alloy have been greatly improved under the combined action of fine grain strengthening and second phase strengthening. The finite element simulation software has been used to simulate the multi-pass cyclic upsetting extrusion. The distribution of different field variables in the process of deformation is revealed. The results show that the distribution of the equal effect force field decreases progressively from the necking region to the top and bottom. In the early stage of deformation, there is an obvious strain gradient from the inside to the outside of the workpiece strain. Among them, the surface strain is the largest (7.3), the bottom strain is the smallest (1.21), the strain difference is 6.09, the strain distribution is not uniform, with the increase of deformation pass, under the action of cumulative strain, When the strain region and the strain uniformity region of the workpiece are expanded for 4 times, the equivalent strain range of different parts of the workpiece reaches 10.5-12.5, the strain inhomogeneity parameter C is reduced from 2.481 to 0.151, and the strain uniformity is improved significantly. The strain uniformity of workpiece has not been further improved. Through the research in this paper, the deformation law of cyclic upsetting extrusion process is grasped, and the best deformation pass of Mg-13Gd-4Y-2Zn-0.5Zr rare earth magnesium alloy is established, which lays a foundation for the popularization and application of this process. It provides guidance and reference for enriching the theory and practice of large member preforming.
【學(xué)位授予單位】：中北大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG306

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