【摘要】：本論文選擇研究較為廣泛的AZ31鎂合金作為研究對(duì)象,通過對(duì)杯形件徑向-反向復(fù)合擠壓工藝中徑向擠壓過程下不同的內(nèi)腔結(jié)構(gòu)(雙錐通道、半圓通道、上半錐通道、下半錐通道以及平底通道),產(chǎn)生剪切變形錐形凸臺(tái)的高度h(h=1mm、h=2mm、h=3mm)及角度?(?=45°、?=60°)以及不同高徑比的坯料?(?=1、?=2、?=4)進(jìn)行了有限元模擬并對(duì)模擬結(jié)果進(jìn)行分析。確定了上半錐通道的內(nèi)腔結(jié)構(gòu)以及h=2mm、?=45°、?=4模具參數(shù)后,進(jìn)行模具設(shè)計(jì)、成形載荷計(jì)算、成形實(shí)驗(yàn);系統(tǒng)的對(duì)徑向-反向復(fù)合擠壓所得的杯形件的五個(gè)典型區(qū)域的微觀組織形貌進(jìn)行分析,得出此工藝在成形過程中的組織演化規(guī)律;對(duì)擠壓成形杯形件的抗拉強(qiáng)度、硬度等力學(xué)性能進(jìn)行測(cè)定;對(duì)杯形件的底部及側(cè)壁部分進(jìn)行了EBSD實(shí)驗(yàn)測(cè)試,分析了成形工藝對(duì)最終側(cè)壁部分的織構(gòu)弱化效果;針對(duì)該成形工藝存在的缺點(diǎn)與不足提出了差速擠壓的新工藝。對(duì)于高強(qiáng)韌鎂合金杯形件的生產(chǎn)具有一定的指導(dǎo)意義。研究表明:(1)上半錐通道模具內(nèi)腔結(jié)構(gòu)以及h=2mm,α=45°參數(shù)條件下的最大成形載荷,平均等效應(yīng)變以及最大損傷值適中,變形較為均勻。隨著錐形凸臺(tái)高度增加,平均等效應(yīng)變?cè)龃?變形逐漸不均勻,成形載荷逐漸增大。高徑比λ=4條件下的成形載荷最小,符合凸模剛度的要求。(2)經(jīng)過徑向-反向復(fù)合擠壓的杯形件側(cè)壁屈服強(qiáng)度與延伸率僅為149.6MPa、17.3%�？估瓘�(qiáng)度為285.3MPa,硬度為70.91HB,要比傳統(tǒng)反擠壓成形的杯形件高30%左右。但屈服強(qiáng)度與延伸率都有所下降。在微觀組織中,側(cè)壁部分的微觀組織呈粗細(xì)晶粒交替分布的雙模態(tài)。經(jīng)過轉(zhuǎn)角后,晶粒沒有明顯的擇優(yōu)取向,合金的漫散性增加,明顯的強(qiáng)織構(gòu)消失,織構(gòu)強(qiáng)點(diǎn)消失,均勻分布于晶粒上,合金的織構(gòu)得到弱化。(3)通過模擬所得壓力值為1.48×106k N、上限法計(jì)算得壓力值為1.93×106k N、實(shí)際成形實(shí)驗(yàn)中的測(cè)量壓力值為1.63×106k N。對(duì)比三組測(cè)量值得出,模擬值要比實(shí)測(cè)值低,上限法值要高于實(shí)測(cè)值。模擬值的誤差為8.67%,上限法的誤差為18.4%。上限法計(jì)算得出杯形件側(cè)壁口部的等效應(yīng)變?yōu)?.933,在有限元模擬結(jié)果中該區(qū)域拾取的四點(diǎn)的等效應(yīng)變平均值為2.895。兩值較為接近,在一定程度上驗(yàn)證了應(yīng)變計(jì)算公式的準(zhǔn)確性。(4)在徑向-反向復(fù)合擠壓基礎(chǔ)之上提出了新型的差速擠壓的階梯通道結(jié)構(gòu),此模具結(jié)構(gòu)有效的增加了金屬的受剪切力次數(shù),明顯增加了等效應(yīng)變值,可能會(huì)機(jī)械破碎粗晶力,等效應(yīng)變?cè)黾?動(dòng)態(tài)再結(jié)晶增加。
[Abstract]:In this paper, AZ31 magnesium alloy, which is widely studied, is selected as the research object. Different inner cavity structures (double cone channel, half circle channel, upper half cone channel) in the radial extrusion process of cup shaped parts are studied. In the lower half cone channel and flat bottom channel, the height h (1 mm / h), the angle (? = 45 擄,? 60 擄) and the billet with different height / diameter ratio (? = 1 / 2 / 2 / 4) of the shearing deformation are simulated by finite element method and the simulation results are analyzed. After determining the inner cavity structure of the upper half conical channel and the 45 擄,? = 4 die parameters, the die design, forming load calculation and forming experiment are carried out. The microstructure morphology of five typical regions of cup shaped parts obtained by radial and reverse composite extrusion is systematically analyzed, and the evolution law of microstructure in the forming process is obtained, and the tensile strength of cup shaped parts formed by extrusion is obtained. The mechanical properties such as hardness were measured, the bottom and side wall of cup were tested by EBSD, and the effect of forming process on the texture weakening of the final sidewall was analyzed. A new technology of differential extrusion is put forward in view of the shortcomings and shortcomings of the forming process. It has certain guiding significance for the production of high strength and toughness magnesium alloy cup. The results show that: (1) the maximum forming load, average equivalent strain and maximum damage value of the upper half conical channel die are moderate, and the deformation is more uniform under the conditions of the cavity structure of the upper half conical channel die and the maximum forming load under the condition of 2 mm, 偽 = 45 擄. With the increase of cone height, the average equivalent strain increases, the deformation becomes inhomogeneous and the forming load increases. Under the condition of height to diameter ratio 位 = 4, the forming load is the smallest, which conforms to the requirement of punch stiffness. (2) the yield strength and elongation of the sidewall of cup parts after radial reverse composite extrusion are only 149.6 MPA / L 17.3. The tensile strength is 285.3 MPA and the hardness is 70.91 HB.This is about 30% higher than that of the cup shaped parts formed by reverse extrusion. But both yield strength and elongation decreased. In the microstructures, the microstructures of the lateral wall show alternate distribution of coarse and fine grains. After the turning angle, the grain has no obvious preferred orientation, the diffuse property of the alloy increases, the obvious strong texture disappears, the texture strength point disappears, and distributes uniformly on the grain. The texture of the alloy is weakened. (3) the simulated pressure value is 1.48 脳 10 ~ 6K N, the upper limit method is 1.93 脳 10 ~ 6K N, and the measured pressure value is 1.63 脳 10 ~ 6K N in the actual forming experiment. Compared with the three groups of measured values, the simulated value is lower than the measured value, and the upper limit value is higher than the measured value. The error of simulation value is 8.67 and that of upper limit method is 18.4. The equivalent effect of the sidewall mouth of the cup is 2.933 calculated by the upper bound method, and the average equivalent strain of the four points picked up by the finite element simulation results is 2.895. The two values are close to each other, which verifies the accuracy of the strain calculation formula to some extent. (4) A new stepped channel structure of differential extrusion is proposed on the basis of radial reverse composite extrusion. The die structure effectively increases the number of shear stress and the equivalent strain value, which may result in mechanical crushing of coarse grain force, increase of equivalent strain and increase of dynamic recrystallization.
【學(xué)位授予單位】：中北大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG146.22;TG379

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