锻态变形铝合金直接半固态等温处理短流程制坯及其触变成形机制

In this project, in order to solve the bottleneck problem of low-cost-fabrication of wrought aluminum semisolid billet with high solid fraction, a novel method called direct semisolid isothermal treatment of wrought aluminum alloy (DSSITWAA) is firstly proposed. In this novel method, deformation storage energy created in elongated grains is used as a recrystallization driving force during the continuous heating course.In addition, equiaxed grains created in hot deformation process also exhibit a microstructure advantage in this novel method. The main research contents include recrystallization mechanism of wrought aluminum alloy during continuous heating, spheroidization mechanism of wrought aluminum alloy during semisolid isothermal treatment, rheological behavior of semisolid billet and quality control of thixoformed products. Low-cost and short-process fabrication of semisolid billet is realized by combining the advantage of commercial mass supply of hot-rolled plates and hot-extruded bars. Low-cost and short-process thixoforming process is also achieved by applying DSSITWAA method to thixoforming process of typical wrought aluminum alloys such as 2A12, 5A06 and 7075 via a general hydraulic press machine. In addition, complex structure components of wrought aluminum alloy with high mechanical properties are thixoformed successfully. It will provide a technology support to forming structure components of wrought aluminum alloy in the fields of aviation, aerospace and automotive.

本项目针对变形铝合金高固相分数半固态坯料难以低成本制备的技术瓶颈问题，利用锻态变形铝合金中拉长晶储存的变形能为连续加热过程中再结晶驱动力，发挥热变形本身产生的等轴晶组织优势，提出锻态变形铝合金直接半固态等温处理的制坯新方法。项目主要研究锻态变形铝合金连续加热过程中再结晶机制、锻态变形铝合金半固态等温过程球化机理、半固态坯料的流变学行为以及半固态触变成形构件的质量调控等内容。结合现有热轧板材和热挤压棒材商业大规模供货的优势，实现变形铝合金半固态坯料短流程和低成本制备。将此制坯方法应用于典型变形铝合金（2A12、5A06、7075等）通用液压机上半固态触变成形技术中，实现了低成本、短流程的半固态触变成形全过程，成形出形状复杂且力学性能高的变形铝合金结构件，为航空、航天、汽车等领域内变形铝合金结构件的成形制造提供技术支撑。

为了适应国家“双碳”的政策方针，结构件的成形制造技术正向着精密、近净成形方向飞速发展。半固态加工结合了传统铸造和锻压工艺的优点，在金属成形方面有着很大的发展前景。短流程、低成本制坯技术是铝合金半固态触变成形技术的核心技术。本项目提出锻态变形铝合金直接半固态等温处理的制坯新方法，揭示了多种铝合金在升温阶段的再结晶机理，探索了铝合金在固态等温处理过程中组织演变规律，阐明了半固态流变学机理及触变成形机制。研究发现，2A12、2A14、6A02和7075等锻态铝合金连续升温过程均发生明显的再结晶现象。锻态铝合金直接进行半固态等温处理可以获得半固态坯料。晶粒尺寸和圆整度由合并长大机制、Ostwald 熟化机制和破碎机制共同决定。半固态等温压缩实验表明当应变速率升高或者温度降低，峰值应力会增加。数值模拟研究表明成形过程中坯料的形状、坯料温度、模具温度和凸模速度对触变成形过程中坯料的温度场、等效应力场和等效应变场存在一定的影响。锻态铝合金直接等温处理法制备的半固态坯料具备较好的触变成形性。固溶和人工时效可使合金的过饱和固溶体中均匀地析出纳米级的G-P区或沉淀过渡相，沉淀相对位错滑移的阻碍可使成形件力学性能的明显提升。固溶和人工时效的热处理工艺适用于触变成形铝合金的强化，但热处理工艺参数与标准热处理工艺参数有所差别。固溶处理时间略长于标准固溶处理时间，固溶温度低于标准固溶温度。本项目发表论文22篇，其中SCI收录17篇，总影响因子为79.123；申请国家发明专利10项，已授权8项；培养研究生9人及黑龙江省高层次人才计划C类人才1人；获得江苏省科学技术奖二等奖和黑龙江省高校科学技术奖一等奖各1项；参加学术会议4人次，做大会报告及分会报告5人次。本项目研究为航空、航天、轨道交通等领域内复杂高性能铝合金结构件的成形制造提供了关键技术支撑。