薄壁铝合金管材缩口热挤压增厚变形行为及组织与性能研究

Tube plastic forming has been an important research and development direction in advanced plastic process technology. Currently, the kind of pull-rod parts in aircraft are fabricated with the method of tube necking and riveting threaded sleeve. The connection strength of pull-rods are instable and their manufacturing costs are high. If the necking of pull-rod parts are used in a new method to thicken the tube wall and attack thread, the method will significantly increase the strength of connection and reduce the cost of the aircraft. So the deformation behavior and microstructure and properties in the thickening process of the necking and hot extrusion of thin-walled aluminum tube is studied in the project. The properties of tube, bar and plate of the same material is different. And the hot extrusion of tube is different from its bending and bulging in stress state. So the tube hot performance test method firstly need to be established and then build the reliable constitutive model of tube. Secondly, the numerical simulations of tube necking and hot extrusion will be used to analyse the strss state and the rheological behavior of the material. On this basis, the heating equipment and die will be designed and the experiment of the tube necking and hot extrusion will becarried on. The influence of forming path, extrusion temperature, extrusion speed, lubrication conditions on the microstructure and properties of the thickening of tube necking and the control method of its microstructure and properties will be explored. Ultimately, a new method and new theory on the thickening of tube necking and hot extrusion will be established and lay a solid theoretical foundation for application of the technology in the aircraft industry.

管材塑性加工是先进塑性加工技术研究与发展的一个重要方向。目前飞机拉杆类零件采用管材缩口成形后铆接螺纹套筒方法制造，连接强度不稳定、制造成本较高。若采用新方法将管材缩口处径向增厚后直接攻螺纹，则将显著增加飞机拉杆的连接强度与降低成本。为此，本项目开展薄壁铝合金管材缩口热挤压增厚变形行为及组织与性能研究。管材与其母材棒料或板料性能不同，而管热挤压与其弯曲、胀形受力状态不同，因此本项目首先需建立管材在热压下性能测试的方法，从而构建管材热压下的可靠本构模型；其次，采用数值模拟，研究管材缩口热挤压受力状态与材料流变行为；在此基础上，设计管缩口热挤压加热装置与模具，开展薄壁铝合金管材缩口热挤压增厚实验研究；并探索成形路径、挤压温度、挤压速度、润滑条件等对缩口增厚处组织与性能的影响规律与控制方法。从而最终建立管材缩口热挤压增厚的新方法、新理论，并为该技术在飞机工业中的应用奠定坚实的理论基础。

目前飞机拉杆类零件采用管材缩口成形后铆接螺纹套筒方法制造，连接强度不稳定、制造成本较高。若采用新方法将管材缩口处径向增厚后直接攻螺纹，则将显著增加飞机拉杆的连接强度与降低成本。为此，本项目开展薄壁铝合金管材缩口热挤压增厚变形行为及组织与性能研究。管材与其母材棒料或板料性能不同，而管热挤压与其弯曲、胀形受力状态不同，因此本项目首先需建立管材在热压下性能测试的方法，从而构建管材热压下的可靠本构模型；其次，采用数值模拟，研究管材缩口热挤压受力状态与材料流变行为；在此基础上，设计管缩口热挤压加热装置与模具，开展薄壁铝合金管材缩口热挤压增厚实验研究；并探索成形路径、挤压温度、挤压速度、润滑条件等对缩口增厚处织与性能的影响规律与控制方法。从而最终建立管材缩口热挤压增厚的新方法、新理论。研究结果表明：（1）采用LF2M 铝合金薄壁管上直接截取环状试样法热压缩试验，铝合金流变应力随变形温度升高而减小；随应变速率的增大而增大。LF2M 铝合金薄壁管材在热压过程中的流变应力满足双曲线正弦本构关系，其热变形材料常数为A=123990.228 s−1，α= 0.00841，n=5.77，其平均激活能为160.67 kJ/mol。 （2）采用模拟软件DEFORM-3D模拟管材缩口增厚，分析成形温度、摩擦系数、凹模锥角等影响因素，得到较优成形工艺参数，有效减少实验次数。（3）设计旋压缩口专用模具；并设计与组装一套加热装置，考虑易产生Euler压杆失稳屈曲，因此在凹模外设置又一冷却装置，管材成形处于差温状态，有助于管材热挤压缩口增厚成形。热挤压缩口增厚成形中采用氮化硼高温润滑剂，其缩口力显著下降，成形稳定，效果良好。优化的热挤压缩口增厚成形工艺参数为：最佳成形温度为450℃，缩口系数为0.75，凹模锥角为20°，进给速度为2mm/s。成形件最大增厚率达到100%以上，且成形质量良好，增厚区组织均匀且晶粒未增大，发生在结晶。