晶体学各向异性效应对铝合金蠕变制造构件性能均匀性的调控机理

In the creep forming of aluminum alloy parts, the forming and age hardening can be proceeded simultaneously, and almost no machining allowance exists.These advantages substantially improve the manufacture efficiency of the creep forming process. However, for some aluminum alloys, the non-uniform response of the textures and the crystallographic characteristics of precipitation (such as the habit plane and the growth direction), which is caused by the applied load, can result in serious anisotropy and reduce the component performance.These problems make the creep forming process difficult to be used in manufacturing the key components (such as the lower-wing structure). In this project, the effects of precipitation orientation on the property anisotropy in the Al alloy single crystals will be firstly investigated. Then, the difference of effective stress in grains with different orientations, which is caused by the texture effect, can be ascertained by the continuum mechanical of textured polycrystals (CMTP) method. Consequently, the effect mechanism and regularity of macro/micro crystallographic anisotropy on the property homogeneity can be revealed. On the basis of the crystallographic anisotropy, the cross-scale constitutive relations of 'stress relaxation - nanoprecipitation - creep strain - property' will be established. The research results can be applied to develop the theory and method in the manufacturing with forming-property coordinated regulation, and promote application of the creep forming process in manufacturing the high-end equipments.

铝合金蠕变成形将成形与时效强化同步进行，制造的壁板几乎没有加工余量，能大幅度提高制造效率。但某些铝合金（如Al-Cu系）由于坯料织构组态、析出强化相的晶体学特性（惯析面与生长方向等）对外加载荷的非均匀响应会导致严重的各向异性，恶化构件性能，使蠕变成形方法难以在关键构件（如机翼下壁板）的制造中获得应用。本项目首先探明在不同方位加载的铝合金单晶体中，强化相析出位向效应对性能各向异性的影响；其次，运用多晶体连续介质力学(CMTP)方法,探明不同取向晶粒由于织构效应引起的有效加载应力差异；从而揭示宏/微观晶体学各向异性效应对性能均匀性的影响机理与规律，并建立基于晶体学各向异性效应的"应力弛豫－纳米强化相析出-蠕变量－性能"跨尺度关联本构关系，发展构件制造形/性协同理论与方法，推进蠕变成形制造方法在高端装备制造中的应用。

蠕变时效成形工艺可同时实现变形和析出强化，制造的构件尺寸精度和性能大幅提高。但对于航空材料常用的Al-Cu（-Mg）系铝合金，板材蠕变时效过程中普遍存在的析出相位向效应导致材料性能不均匀，限制了该工艺在航空材料中的应用。本项目为了研究晶体学各向异性对应力时效中析出位向效应的影响，从单晶过渡到具有多种复杂取向的多晶，研究了多种不同取向Al-2Cu单晶的应力时效行为，建立了基于晶体学各向异性的Al-Cu合金应力时效强化模型。分别研究了同一取向单晶在不同应力大小（(-1,1,6)取向，15MPa，40MPa，60MPa）下应力时效；同一应力大小（40MPa）下，不同取向单晶的应力时效行为。通过分析时效后析出相的TEM图片和力学性能的结果，发现Al-Cu合金应力时效后的硬度及屈服强度不仅取决于时效过程中加载应力的大小，不同的晶体学取向也会影响其力学性能。(-1,1,6)取向的单晶由于最接近θ’析出相的(001)惯习面，离(111)位向效应弱取向也较近，所以其析出强化效果较强；而(-1,3,3)离(001)惯习面和(111)取向均最远，析出强化效果最弱。基于不同晶体学取向的Al-1.2Cu-0.5Mg单晶在不同应力大小下应力时效的实验结果，考虑材料自身的织构组态，加载应力对析出相尺寸和分布的影响，以及应力诱发的位错抑制位向效应的作用，建立了晶体学各向异性的应力时效析出强化模型，为过渡到以S相为主要强化相的具有多种复杂取向的2系铝合金材料提供理论基础。