摘要
High-angle annular dark-field scanning transmission electron microscopy and selected area electron diffraction techniques were used to study the mechanism that underlies the influence of rapid cold-stamping deformation on the fracture behavior of the elongated nanoprecipitated phase in extruded Al−Cu−Mg alloy.Results show that the interface between the long strip-shaped S′phase and the aluminum matrix in the extruded Al−Cu−Mg alloy is flat and breaks during rapid cold-stamping deformation.The breaking mechanisms are distortion and brittle failure,redissolution,and necking.The breakage of the long strip S′phase increases the contact surface between the S′phase and the aluminum matrix and improves the interfacial distortion energy.This effect accounts for the higher free energy of the S′phase than that of the matrix and creates conditions for the redissolution of solute atoms back into the aluminum matrix.The brittle S′phase produces a resolved step during rapid cold-stamping deformation.This step further accelerates the diffusion of solute atoms and promotes the redissolution of the S′phase.Thus,the S′phase necks and separates,and the long strip-shaped S′phase in the extruded Al−Cu−Mg alloy is broken into a short and thin S′phase.
采用高角度环形暗场(HAADF)扫描透射电子显微镜(STEM)和选区电子衍射(SAED)技术,研究快速冷冲强变形对挤压态Al−Cu−Mg合金长片状纳米析出相破断行为的影响机理。实验结果表明:挤压态Al−Cu−Mg合金中长片状S′相与铝基体界面平整,在快速冷冲强变形过程中发生明显破断,其破断机制主要为扭曲、脆断、回溶和缩颈。长片状S′相的破断,增加了S′相与铝基体的接触面,提高了界面畸变能,从而导致S′相的自由能高于基体自由能,为溶质原子回溶至铝基体的扩散创造条件。脆性S′相在快速冷冲强变形过程中产生“回溶台阶”,进一步加速溶质原子的扩散,促进S′相的回溶,造成S′相缩颈而导致各部分的分离,从而使挤压态长片状S′相“碎化”成短而细的S′相。
基金
Project(19A131)supported by Key Scientific Research Project of Hunan Province,China
Project(2019JJ60050)supported by the Natural Science Foundation of Hunan Province,China。
