基于冷轧变形诱发析出相溶解及再时效的6000系铝合金强韧化机理研究

Up to now, it is still a fundamental scientific issue to improve both the strength and toughness/ductility of metallic structural materials simultaneously, and meanwhile the resulted solution should have a broad prospect in industrial application. For age-hardenable 6000 series Al alloys with wide applications in aerospace, automobile and rail transit, etc. a novel thermo-mechanical treatment consisted of pre-ageing, conventional cold-rolling and re-ageing was presented, based on the formation of supersaturated solid solution by cold-rolling induced dissolution of precipitates and further re-ageing. Preliminary results showed that the treatment could improve the strength and ductility of 6000 series Al alloys and then had good application prospects. . In order to understand deeply the effects of microstructures on mechanical behavior of 6000 series Al alloys during the thermo-mechanical treatment, the following aspects will be investigated in the present application, including the factors, micro-process and dissolution mechanism during the formation of supersaturated solid solution based on cold-rolling induced dissolution of precipitates; the precipitation process and recovery and recrystallization behavior of the supersaturated solid solution during re-ageing; quantitative and qualitative analyses of the dislocation density, precipitate, grain size and texture during the thermo-mechanical treatment and their strengthening contributions; the effect of re-precipitates and recovery and recrystallization on the dislocation accumulating ability of the re-aged alloy during tensile testing and the toughening mechanism. The above research founding will help to develop high performance Al alloys of our own independent intellectual property rights.

如何在不降低韧/塑性基础上大幅提高强度，一直是金属材料研究领域的重大基础科学问题；同时，研究形成的解决方法还应具有广阔工业应用前景。针对广泛用于航天航空、汽车、轨道交通的6000系铝合金，申请人基于冷轧变形诱发析出相溶解形成过饱和固溶体及其再时效行为，提出一种新型形变热处理-预时效+冷轧变形+再时效，初步实现上述目标。为了深入掌握形变热处理过程中微观组织演变规律及其对6000系铝合金力学行为的影响机理，本项目深入研究冷轧变形诱发析出相溶解形成过饱和固溶体的影响因素、微观过程及溶解机制；研究再时效过程中过饱和固溶体的析出行为及回复和再结晶规律；定性和定量研究形变热处理过程中位错密度、析出相、晶粒尺寸和织构特征的演变规律及强化贡献，揭示强化机理；弄清再时效析出相及回复和再结晶对位错累积行为的影响规律，揭示韧化机理。项目研究成果将为开发具有我国自主知识产权的高性能铝合金奠定坚实理论和实践基础。

为了适应航空工业对轻质、高强度、高韧性及耐腐蚀铝合金薄板的迫切需求，基于预时效析出相在冷轧变形过程中溶解、继而再时效析出的这一观点，本项目采用拉伸性能测试和加速腐蚀试验相结合，研究了预时效状态、冷轧压下量、再时效工艺等对6000系铝合金拉伸性能和晶间腐蚀敏感性的影响规律，并采用光学金相、透射电镜、扫描电镜、X射线衍射仪、织构仪、电子背散射衍射、电化学工作站等方法，定性和定量研究了不同处理阶段微观组织的演变规律，包括晶粒形态与尺寸、位错密度、析出相性质、形貌、数量与体积分数、织构类型与体积分数等。主要研究成果如下：（1）基于预时效、冷轧及再时效这一形变热处理方法，能够同时实现时效硬化型6000系铝合金高强度、高韧性及高耐蚀性三者有机结合，并且，该工艺也适用于2000系和7000系铝合金；（2）提出合金强化是析出强化、位错强化、织构强化、细晶强化等多因素综合作用结果；提出合金韧化是再时效过程中回复降低位错密度降低和析出相阻碍位错滑移，进而提高合金存储位错能力的结果；合金耐蚀性的提高是形变诱导初始晶界形成小晶粒、晶界附近位错抑制过饱和溶质院子扩散进入晶界、晶界位错加速析出相粗化，进而扩大晶界析出相间距、切断沿晶连续阳极溶解通道等多因素作用结果；（3）提出的形变热处理方法是基于铝合金薄板的常规生产流程而开发的，因此，具有良好的工业应用前景。