复杂中空铝合金型材聚氨酯芯等径角挤压的性-形协同调控变形机理

Both material and structure lightweights of the hollow aluminum alloy should be supported by its mechanical properties. Its complex cross section shapes also require more high precision of shape-position. During Equal Channel Angular Pressing (ECAP) with polyurethane mandrel, the mechanical properties of profiles can be improved by the refined grains formed under radial shear stress, the precisions of shape-position can be also kept by controlling cross section principle strain. However, the existing reports are only focused on regulation results of mechanical properties or shape-position precisions during the circle tube ECAP with polyurethane mandrel, respectively. Based on analytic methods, revealing the deformation mechanisms for the mechanical properties and shape-position precisions coordinate regulation of complex hollow cross section profiles during ECAP with polyurethane mandrel are uncommon. In this project, principal stress method is used to analyze the hollow aluminum alloy during ECAP with polyurethane mandrel. The analytical general solution for pressing stress of complex hollow cross section profiles is obtained. Both mandrel self-sealing and stable extrusion conditions are received. Based on the distribution proportion functions of radial shear stress and cross section principal strain, the transfer behaviors of both stress and principal strain are yielded. Then the deformation mechanisms for mechanical properties and shape-position precisions coordinate regulation of hollow aluminum alloy during ECAP with polyurethane mandrel are revealed. Through continued ratio of the functions, geometric application conditions of the mechanisms are extended to complex cross section profiles. Based on both physical and finite element simulation experiments, the analytical results are proved. The theoretical support of mechanics is provided to have both good mechanical properties and shape-position precisions of complex hollow cross section aluminum alloy profiles during ECAP.

中空铝合金型材的材料、结构双重轻量化需以力学性能为保证，其复杂的断面形状也对形位精度提出了更高要求。填加聚氨酯芯后的型材在等径角挤压中，可由径向剪应力引起晶粒细化提升力学性能，并通过对断面主应变的控制保持形位精度，但现有报道多针对简单管材独立验证聚氨酯芯等径角挤压的性、形调控结果，鲜有从成形力学解析角度揭示复杂中空型材聚氨酯芯等径角挤压的性-形协同调控变形机理。本项目拟采用主应力法解析中空铝合金型材聚氨酯芯等径角挤压过程，获得复杂中空型材挤压应力解析通解，取得芯材自封闭与稳定挤压条件，由径向剪应力与断面主应变的分布比例函数分别阐明各自传递行为，共同揭示聚氨酯芯等径角挤压中空铝合金型材性-形协同调控的变形机理，将该机理的几何适用条件以分布比例函数连比形式扩展至复杂断面型材，依据有限元与物理挤压实验验证解析结果，为由等径角挤压获得复杂断面中空铝合金型材良好的力学性能与形位精度提供力学理论支撑。

中空铝合金型材的材料、结构双重轻量化需以力学性能为保证，其复杂的断面形状也对形位精度提出了更高要求。填加聚氨酯芯后的型材在等径角挤压中，可由径向剪应力引起晶粒细化提升力学性能，并通过对断面主应变的控制保持形位精度，但现有报道多针对简单管材独立验证聚氨酯芯等径角挤压的性、形调控结果，鲜有从成形力学解析角度揭示复杂中空型材聚氨酯芯等径角挤压的性-形协同调控变形机理。本项目拟采用主应力法解析中空铝合金型材聚氨酯芯等径角挤压过程，获得复杂中空型材挤压应力解析通解，取得芯材自封闭与稳定挤压条件，由径向剪应力与断面主应变的分布比例函数分别阐明各自传递行为，共同揭示聚氨酯芯等径角挤压中空铝合金型材性-形协同调控的变形机理，将该机理的几何适用条件以分布比例函数连比形式扩展至复杂断面型材，依据有限元与物理挤压实验验证解析结果，为由等径角挤压获得复杂断面中空铝合金型材良好的力学性能与形位精度提供力学理论支撑。.在项目研究中，申请者分别选取了铝合金方管、U-型管以及更为复杂的型材在聚氨酯材料的辅助下完成了等径角挤压过程，通过晶粒形貌等特征验证了材料力学性能的提升。同时通过实验和有限元的仿真测量获得了型材变形后形位控制良好的结论。为进一步明确该过程的控形调性机理，项目完成了变形过程的解析，并通过解析表达式明确了调性过程中，各个铝合金微元的厚度会以等比例变化维持微元体初始的厚度比值，最后在等径角通道中借助等尺寸通道的等比例变形过程形成控形机制。.在项目研究中，申请者还进一步发现可以基于聚氨酯材料的应力传递机制将其应用在了对板材的拉深变形中，将型材变形过程的应力传递机制进一步推广，获得了形位尺寸精度良好同时能够完好成形的板材微通道。.另外申请者也同时注意到固体连续介质芯材对于形状改变的变形过程传力和变形能力有限，并且在变形中芯材也受制于温度，因此项目提出进一步采用砂芯为传力介质获得了更好的三通接头成形结果。