高强铝合金热变形行为研究

发布时间：2018-07-17 00:55

【摘要】：7000系列和2000系列铝合金同属于高强度铝合金，广泛用于航空航天领域，它们都有着“不可焊金属”之称。搅拌摩擦焊从根本上解决了高强铝合金的难焊问题，实际焊接过程中焊接温度以及金属的塑性流动对焊缝成型非常重要，因此关于两种合金热变形行为的研究对弄清焊接机理及焊接工艺优化有重要意义。 本文采用物理模拟的方法，利用Gleeble-3500热模拟机分别采用拉伸和压缩的方法，系统地研究了7050和2024铝合金的热变形行为。从流变应力上看，两种合金的变化规律类似，，受应变速率和温度影响显著。总体上流变应力随温度的升高和应变速率的降低而减小。 对于拉伸变形，以断面收缩率和延伸率为塑性指标结合金相组织照片，讨论了温度和应变速率对金属塑性的影响，并建立了热变形本构方程。结果表明：两种合金塑性都随着变形温度的升高及应变速率的降低而升高。7050铝合金与2024铝合金相比，热变形激活能Q更小，这说明前者更容易发生动态再结晶。实验条件下，7050铝合金主要软化机制为动态再结晶，其在400℃时塑性最好，2024铝合金主要软化机制为动态回复，无塑性最高点。 对于压缩变形，同样建立了热变形本构方程，基于动态材料模型（DMM）和Prasad的失稳准则，给出了不同形变参数下的应变速率敏感指数(m)、能量消耗效率(η)及流变失稳区域，并最终绘制出热加工图。结合热加工图及金相照片得出了合适的合金加工工艺，同时对试样内部由于应变分布不一而引起的组织不均匀性进行了分析。结果表明：7050铝合金在400℃低应变速率下发生动态再结晶，适合热加工。2024铝合金在250~300℃，低应变速率下存在流变失稳区，不适合加工；400℃以上出现能量耗散效率η的峰值，适合进行热加工，软化机制以动态回复为主。
[Abstract]:7000 series and 2000 series aluminum alloy are both high-strength aluminum alloys, widely used in aerospace field, they are known as non-weldable metals. Friction stir welding (FSW) fundamentally solves the problem of high strength aluminum alloy welding. The welding temperature and the plastic flow of metal are very important to weld forming in the actual welding process. Therefore, the study on the hot deformation behavior of the two alloys is of great significance to clarify the welding mechanism and welding process optimization. In this paper, the thermal deformation behavior of 7050 and 2024 aluminum alloys has been systematically studied by means of physical simulation and Gleeble-3500 thermal simulator using tensile and compression methods, respectively. From the point of view of rheological stress, the changes of the two alloys are similar, and are significantly affected by strain rate and temperature. As a whole, the flow stress decreases with the increase of temperature and the decrease of strain rate. For tensile deformation, the effects of temperature and strain rate on metal plasticity were discussed, and the constitutive equation of thermal deformation was established. The results show that the plasticity of the two alloys increases with the increase of deformation temperature and the decrease of strain rate. Compared with 2024 aluminum alloy, the hot deformation activation energy Q is smaller, which indicates that the former is more prone to dynamic recrystallization. Dynamic recrystallization is the main softening mechanism of 7050 aluminum alloy under the experimental conditions, and the main softening mechanism of 2024 aluminum alloy is dynamic recovery at 400 鈩

本文编号：2128316