基于准二维多晶试样的时效析出相对铝合金变形机制影响的定量研究

Precipitation strengthening is the dominant mechanism for heat-treatable aluminium alloy strengthening, and ductility improvement without scarification of strength by tuning precipitates attracts increasing attentions. However, the influence of precipitates on deformation mechanisms has not been fully investigated, which results to insufficient understanding of their effects on ductility. The project aims on Al-1Mg-0.3Si quasi-2D multicrystal samples, including solid solution samples, samples with spherical pre-β” precipitates and samples with needle-shaped β” precipitates. Firstly, to study the activities of slip systems in these three kinds of samples according to slip trace analysis; Secondly, to calculate the strain distribution based on Green-Lagrange strain tensor and von Mises strain; Furthermore, to calculate the shear in each activated slip system and strain due to grain boundary sliding based on the analysis of slip system activities and strain distribution, and then to quantitatively investigate the effects of precipitates (pre-β” precipitates and needle-shaped β” precipitates) on deformation mechanisms in aluminum alloy at micron scale. This work can contribute to a better understanding of the effects of precipitates on ductility, and provide both theoretical and practical fundamentals for developing new generation ductile Al alloys with high strength.

时效析出强化是时效铝合金获得高强度的主要因素, 通过调节时效析出相在不牺牲强度的同时提升铝合金塑性成为材料工作者近来关注的热点。但时效析出相对铝合金变形机制的影响尚未得到系统研究，限制了关于其对塑性影响机制的理解。本项目拟以Al-1Mg-0.3Si合金准二维多晶试样（固溶体试样、含球状pre-β”相和含针状β”相试样）为研究对象，根据滑移迹线分析三种试样变形过程中滑移系的激活规律，运用网格法计算局部应变（Green-Lagrange应变张量和von Mises应变），并基于滑移系激活规律和局部应变计算各滑移系切应变和晶界滑动所引起的应变。从微米尺度定量分析时效析出相（pre-β”相和β”相）对铝合金变形机制的影响，加深关于时效析出相对铝合金塑性影响机制的理解，为新型高塑性、高强度铝合金的开发提供理论和实验依据。

同时获得高强度和高塑性是材料研究人员关心的热点问题。作为一种强化机制，析出强化可显著提高材料的强度，但是通常会降低塑性。因此，探明析出相对塑性的影响机制，可为通过调控析出相在提高强度的同时减少对塑性的影响，从而获得最优的综合力学性能提供理论支撑。本项目以准二维Al-1Mg-0.3Si 多晶试样为研究对象，针对含不同时效析出相（β”相和β’相）的样品，采用滑移迹线分析（slip trace analysis）、高分辨数字图像相关技术（High resolution digital image correlation, HRDIC）和透射电子显微镜（Transmission electron microscopy, TEM）等方法研究了析出相对变形机制和应变分布的影响，以及析出相与位错的交互作用，探明了析出相对塑性的影响机理。主要结果如下：1)以β”相为主要析出相的试样较以β”相为主要析出相的试样具有更好的塑性；2）固溶体试样和以β”相为主要析出相的试样在拉伸过程中，晶粒内会有多个滑移系被激活，而在以β’相为主要析出相的样品中，只有单个滑移系被激活，说明β”相对滑移系激活的影响更小；3）固溶体试样和以β”相为主要析出相的试样在变形过程中的应变分布更加均匀，而以β’相为主要析出相的试样的应变梯度更大；4）塑性变形过程中，位错绕过β”相进行滑移，而通过切过β’相的方式进行滑移。因此，以β”相为主要析出相的试样的塑性变形更加均匀，而以β’相为主要析出相的试样的塑性变形均匀性较差。可见，生成与基体共格的β”相可在提高强度的同时，使合金保持较好的塑性。