镁合金正挤压—弯曲剪切复合连续变形模具型腔设计及工艺参数优化

发布时间：2019-04-09 13:08

【摘要】：镁合金因其优良的物理力学性能,在航空、航天、军工以及民用等领域应用较为广泛。目前,有关变形镁合金大塑性变形技术的研究报道较多,但多数大塑性变形方法存在生产效率低、成本高、工艺复杂且无法实现连续生产等问题。本文研究了一种集正挤压与多次弯曲剪切于一体的棒-板正挤压-弯曲剪切复合连续成形新工艺(Direct Extrusion and Bending Shearing,DEBS)。以商用铸态AZ31镁合金为研究对象,通过塑性力学理论计算、有限元数值模拟以及实验等手段对该工艺进行了多方面研究,主要包括:挤压力、应变和应变率的理论计算;模具型腔设计及工艺参数优化;DEBS镁板力学性能和微观组织的检测与分析等等。所获得的研究成果如下:(1)DEBS复合成形工艺的理论分析。将上界法和有限元数值模拟方法相结合,引入形状复杂系数,对棒-板正挤压-弯曲剪切复合连续变形工艺所需的挤压力及各阶段的应变、应变率和变形速率因子(Z参数)进行了理论计算。通过试验研究验证了计算结果的可靠性,可为模具型腔设计及挤压机型号的合理选择提供理论指导。(2)DEBS模具型腔设计。以平均挤压载荷Favg、速度场相对标准偏差VRSDV、应变均值εavg和应变相对标准偏差εRSDV为定量化评价指标,运用DEFORM-3D有限元数值拟软件对DEBS挤压过程进行了模拟分析,得出了各结构参数对成形结果的影响规律。结果表明:对于DEBS复合挤压工艺,当锥角φ为120o、挤压通道弯曲角β为150o、挤压通道弯曲角Ψ为110o、挤压通道弯曲过渡半径R1为6 mm、定径区长度L5为12 mm时,所获得的的镁合金板材(横截面:25 mm×3 mm)质量较佳。(3)DEBS工艺参数优化。选用已设计好的DEBS模具作为研究基础,在不同的工艺条件下,采用有限元软件对DEBS挤压过程进行了模拟分析,并研究了各工艺参数对成形结果的影响规律。研究结果表明:当挤压温度为370℃、挤压速度为2 mm·s-1时,有利于保证板材的质量。(4)实验验证与分析。在数值模拟分析结果的指导下,成功实现了DEBS挤压试验,并对DEBS镁板的力学性能和微观组织进行了检测分析。结果表明:(1)DEBS复合工艺可显著地改善镁合金的微观组织与综合力学性能。(2)当挤压温度为370℃、挤压速度为2 mm·s-1时,经一道次成形后平均晶粒尺寸由原始铸态的240μm可细化至6μm以下,抗拉强度与屈服强度分别为300 MPa、220 MPa,室温断裂延伸率可高达25.7%,这也验证了工艺参数优化结果的合理性。(3)由挤压力测试值与数值模拟值对比分析可知,相对误差在10%以内,可以满足工程计算要求,验证了数值模拟结果的可靠性。
[Abstract]:Magnesium alloys are widely used in aviation, aerospace, military and civil fields due to their excellent physical and mechanical properties. At present, there are many reports about the large plastic deformation technology of wrought magnesium alloy, but most of the large plastic deformation methods have some problems such as low production efficiency, high cost, complicated process and unable to realize continuous production, and so on. In this paper, a new continuous forming process (Direct Extrusion and Bending Shearing,DEBS) of bar-sheet forward extrusion-bending shear combined with forward extrusion and multiple bending shear is studied. Taking commercial as-cast AZ31 magnesium alloy as research object, many aspects of the process were studied by means of plasticity theory calculation, finite element numerical simulation and experiment, including the theoretical calculation of extrusion pressure, strain and strain rate; Die cavity design and process parameters optimization; DEBS magnesium plate mechanical properties and microstructure detection and analysis, and so on. The research results are as follows: (1) theoretical analysis of DEBS composite forming process. Combining the upper bound method with the finite element numerical simulation method, the complex shape coefficient is introduced, and the extrusion pressure and the strain of each stage of the bar-plate extrusion-bending shear composite continuous deformation process are studied. The strain rate and deformation rate factor (Z parameter) are calculated theoretically. The reliability of the calculated results is verified by experimental research, which can provide theoretical guidance for die cavity design and reasonable selection of extruder type. (2) DEBS die cavity design. Taking Favg, velocity field relative standard deviation (VRSDV,) and strain relative standard deviation (蔚 RSDV) of average extrusion load as quantitative evaluation indexes, the process of DEBS extrusion is simulated and analyzed by DEFORM-3D finite element simulation software. The influence of structural parameters on the forming results is obtained. The results show that when the cone angle 蠁 is 120o, the extrusion channel bending angle 尾 is 150o, the extrusion channel bending angle is 110o, and the extrusion channel bending transition radius R1 is 6 mm, sizing zone length L5 is 12 mm. For DEBS composite extrusion process, the bending angle of extrusion channel is 110o, the bending angle of extrusion channel is 150o, the bending angle of extrusion channel is 110o. The obtained magnesium alloy sheet (cross section: 25 mm 脳 3 mm) is of better quality. (3) the process parameters of DEBS are optimized. Based on the designed DEBS die, the process of DEBS extrusion was simulated and analyzed by finite element software under different process conditions, and the influence of various process parameters on the forming results was studied. The results show that when the extrusion temperature is 370C and the extrusion speed is 2 mm 路s-1, the quality of the sheet is guaranteed. (4) the experimental verification and analysis are carried out. Under the guidance of numerical simulation and analysis, the DEBS extrusion test was successfully carried out, and the mechanical properties and microstructure of DEBS magnesium plate were tested and analyzed. The results show that: (1) the microstructure and comprehensive mechanical properties of magnesium alloy can be significantly improved by DEBS composite process. (2) when the extrusion temperature is 370C and the extrusion speed is 2 mm 路s-1, the microstructure and mechanical properties of magnesium alloy can be improved obviously. After one-pass forming, the average grain size can be refined from 240 渭 m to less than 6 渭 m, and the tensile strength and yield strength can be up to 25.7% at room temperature, respectively, when the tensile strength and yield strength are 300 MPa,220 MPa, respectively, and the average grain size can be refined from 240 渭 m to less than 6 渭 m. This also verifies the rationality of the optimization results of process parameters. (3) through the comparative analysis of extrusion pressure test values and numerical simulation values, the relative error is less than 10%, which can meet the requirements of engineering calculation and verify the reliability of numerical simulation results.
【学位授予单位】：湖南科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG379

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