镁合金杯形件径向—反向复合挤压成形数值模拟与微观组织演化研究

发布时间：2018-10-17 17:59

【摘要】：本论文选择研究较为广泛的AZ31镁合金作为研究对象,通过对杯形件径向-反向复合挤压工艺中径向挤压过程下不同的内腔结构(双锥通道、半圆通道、上半锥通道、下半锥通道以及平底通道),产生剪切变形锥形凸台的高度h(h=1mm、h=2mm、h=3mm)及角度?(?=45°、?=60°)以及不同高径比的坯料?(?=1、?=2、?=4)进行了有限元模拟并对模拟结果进行分析。确定了上半锥通道的内腔结构以及h=2mm、?=45°、?=4模具参数后,进行模具设计、成形载荷计算、成形实验;系统的对径向-反向复合挤压所得的杯形件的五个典型区域的微观组织形貌进行分析,得出此工艺在成形过程中的组织演化规律;对挤压成形杯形件的抗拉强度、硬度等力学性能进行测定;对杯形件的底部及侧壁部分进行了EBSD实验测试,分析了成形工艺对最终侧壁部分的织构弱化效果;针对该成形工艺存在的缺点与不足提出了差速挤压的新工艺。对于高强韧镁合金杯形件的生产具有一定的指导意义。研究表明:(1)上半锥通道模具内腔结构以及h=2mm,α=45°参数条件下的最大成形载荷,平均等效应变以及最大损伤值适中,变形较为均匀。随着锥形凸台高度增加,平均等效应变增大,变形逐渐不均匀,成形载荷逐渐增大。高径比λ=4条件下的成形载荷最小,符合凸模刚度的要求。(2)经过径向-反向复合挤压的杯形件侧壁屈服强度与延伸率仅为149.6MPa、17.3%。抗拉强度为285.3MPa,硬度为70.91HB,要比传统反挤压成形的杯形件高30%左右。但屈服强度与延伸率都有所下降。在微观组织中,侧壁部分的微观组织呈粗细晶粒交替分布的双模态。经过转角后,晶粒没有明显的择优取向,合金的漫散性增加,明显的强织构消失,织构强点消失,均匀分布于晶粒上,合金的织构得到弱化。(3)通过模拟所得压力值为1.48×106k N、上限法计算得压力值为1.93×106k N、实际成形实验中的测量压力值为1.63×106k N。对比三组测量值得出,模拟值要比实测值低,上限法值要高于实测值。模拟值的误差为8.67%,上限法的误差为18.4%。上限法计算得出杯形件侧壁口部的等效应变为2.933,在有限元模拟结果中该区域拾取的四点的等效应变平均值为2.895。两值较为接近,在一定程度上验证了应变计算公式的准确性。(4)在径向-反向复合挤压基础之上提出了新型的差速挤压的阶梯通道结构,此模具结构有效的增加了金属的受剪切力次数,明显增加了等效应变值,可能会机械破碎粗晶力,等效应变增加,动态再结晶增加。
[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 掳,? 60 掳) 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 掳,? = 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, 伪 = 45 掳. 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.
【学位授予单位】：中北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.22;TG379

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