超细晶Al-Cu-(Sc)合金的时效析出特性与力学性能研究

Precipitating nanosized second particles within the grain interior is an effective approach to increase the strength and simultaneously improve the ductility of ultrafine-grained alloys. It is thus necessary to in-depth understand the precipitation characteristics at submicrometer scale length as well as their controling factors. In this project, the precipitation behaviors and mechanical properties of ultrafine-grained Al-Cu-(Sc) alloys will be systematically investigated. The ultrafine-grained alloys, prepared by using equal channel angular pressing (ECAP) method, will undergo different aging treatment at low temperatures with a series of aging times. Evolution in microstructure and precipitation characteristics will be carefully examined by using various advanced analyzing techniques such as TEM, EBSD, and etc. Mechanical properties will be evaluated through uniaxial testing and nanoindentaion measurement, respectively. By establishing quantitative relationships among pressing-microstructure- precipitation -properties, the following concerns will be clearly revealed: (1) the influence of grain size, grain boundary type, dislocation density, and alloy composition on the precipitation behaviors at submicrometer scale length; (2) the influence of minor Sc additive on the precipitation sequence/behaviors and its underlying mechanism; (3) the influence of precipitation on mechanical properties of ultrafine grained Al-Cu-(Sc) alloys, including yield strength, ductility, strain hardening, strain rate sensitivity, and so on. The results produced from this project should provide both experimental and theoretical references to the design of microstructure, optimization of ECAP/aging technologies, and choice of microalloying element for ultrafine-grained alloys

同时提高超细晶合金强度和延性的一种有效途径是在晶粒内弥散析出纳米第二相颗粒，因此需要深入了解亚微米晶粒尺度下的时效析出特性及其影响因素。本申请拟通过等径角挤压制备Al-Cu-(Sc)超细晶合金，经不同低温时效处理，分别采用透射电子显微镜、电子背散射衍射技术等手段表征微观组织演变及时效析出行为，采用单轴拉伸和纳米压入评价力学性能变化。通过建立挤压工艺-微观组织-时效行为-力学性能之间的联系，阐明：(1) 超细晶Al-Cu合金的时效析出特性与晶粒尺寸约束效应，晶粒尺寸/形貌、晶界状态、位错密度等初始微观组织和合金成分等对时效行为的影响；(2) 微量Sc元素的适量添加及其对时效析出次序和析出动力学影响的作用机理；(3) 亚微米尺度下时效析出行为对强度、延性、应变硬化等力学性能的影响及其强韧化机理。研究结果可为探索超细晶结构下的组织成分设计、制备/时效工艺优化和微量元素选择提供理论基础。

以Al-Cu模型材料和微量添加Sc的Al-Cu-Sc合金作为研究对象，采用等通道挤压制备得到了粗晶、细晶和超细晶的不同微观组织，系统重点研究了晶粒尺寸变化以及微合金Sc元素对时效析出行为及最终力学性能的影响。取得的主要研究进展如下：(1) 时效析出强烈地依赖于晶粒尺寸，随着晶粒尺寸减小，晶界析出占主导，并逐渐消耗晶内析出。超细晶Al-Cu合金中完全为晶界平衡相Al2Cu析出，材料强度低、延性差；(2) 0.3wt%Sc添加具有明显的微合金化作用，有效地抑制了晶界析出并促进了晶内强化相的弥散分布。Sc微合金效果在超细晶下最明显，与未添加Sc的Al-Cu超细晶合金相比，Al-Cu-Sc超细晶合金的屈服强度和延伸率分别提高了50%和275%；(3) 修正了粗晶合金中的析出热/动力学模型，提出了适合超细晶铝合金的时效析出模型，能很好地模拟超细晶Al-Cu-Sc合金析出相参数的演变。. 本项目的研究结果不但有利于深入理解Al-Cu合金时效析出行为的晶粒尺度效应和微合金化效应，同时还能为实际工业应用中不同晶粒尺度下的微合金化设计提供理论基础与参考借鉴。