铝合金超低温轧制变形机理及工艺优化基础研究

The microstructures and properties of the aluminum alloy sheets as well as their distribution produced by modern cold or hot rolling techniques cannot satisfy the application requirements of the national major areas such as the aerospace. The main causes should be that the deformation temperature and deformation-induced thermal effects during cold or hot rolling have greatly promoted the recovery and recrystallization, which can weaken the ability of grain refinement. Presently, the 90 % rolling reduction as well as significantly improved strength of high-strength aluminum alloy has been successfully obtained by cryo-rolling in our team. However, there is not direct and reasonable understanding about the corresponding forming mechanism on this excellent cryo-deformation ability. Basing on obtaining good cryo-rolling processes for high-strength aluminum alloy, this project intends to characterize the evolution of microstructures, dislocation defect and others during the cryo-rolling process, and the effect of temperature on the evolution of defects will be theoretically analyzed with microscopic examination of the dislocations. With finite element modelling of the cryo-rolling process using cryogenic constitutive model of high-strength aluminum alloy, the relationship between plastic deformation and temperature/strain will be analyzed and cognized as well as the effect of temperature on the aging action so that the forming mechanism about the prominent cryo-deformation ability can be uncovered. Moreover, the effect of much high stored energy induced by cryo-rolling to the room temperature storage and recrystallization/aging treatments and others of the cryo-rolling high-strength aluminum alloy will be the key part to achieve the strengthening and toughening of the alloy with the investigation and understanding of the corresponding strengthening mechanism.

现有热、冷轧制铝合金板材在组织、性能及其均匀性等方面无法满足航空航天等国家重大工程领域的应用需求，主因在于冷、热轧制中温度及变形热效应对回复和再结晶的有利促进使得组织细化能力减弱。项目组探索研究发现超低温下可使高强铝合金实现高达90%的轧制变形,并显著提升合金强度,但对这种优异超低温轧制变形能力的形成机理尚无直接、合理的理解和认识。本项目拟在获得优化的高强铝合金板材超低温轧制加工工艺基础上,开展超低温轧制过程中组织、位错缺陷等演变的表征,并就缺陷变化的温度效应进行微观表征和理论分析；同时基于超低温本构模型与有限元模拟研究来分析和认知超低温下塑性变形与温度、应变间的关联性及温度对合金时效特性的影响,从而结合起来揭示优异超低温变形能力的形成机理。与此同时，超低温轧制变形引入的高变形储能对后续室温存储和再结晶/时效热处理等的影响及合金强化机理的研究和理解是实现合金强韧化的关键环节。

系统研究了应变硬化型5052和时效硬化型高强铝合金的超低温变形加工与后续热处理工艺及内在变形机制和强化机理，并将超低温变形加工技术应用于亚稳奥氏体不锈钢的加工处理；研究了高强铝合金的加工性能及热变形机理。（1）掌握了铝合金超低温变形加工技术与后续热处理工艺，显著弱化退火态5052铝合金织构的同时，使O态屈服强度较室温轧制合金提高~33%，优于现有商用5052-O合金板材及高牌号5000系铝合金性能；实现了难变形高强7000系铝合金的大变形量超低温轧制变形，使合金强度提高~20%，直接时效处理使超低温轧制合金屈服强度较传统热轧合金提高70MPa以上，延伸率可达8%以上。（2）超低温变形加工可快速促进304亚稳奥氏体不锈钢中形变诱导马氏体转变，但未改变马氏体与母相奥氏体间取向关系，后续再结晶处理后平均晶粒尺寸达4-5μm，且屈服和抗拉强度分别达到360MPa和800MPa以上，明显优于太钢等企业生产的304奥氏体不锈钢薄板性能。（3）构建了激活能演变的高强7050铝合金热变形本构方程和唯理性本构方程，确定了较佳的加工工艺窗口和热变形机理。本项目取得的研究成果可为铝合金及其他系列合金提供一种低成本、高效加工处理技术，可显著提升强塑性和改善变形能力。