Abstract: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.

Key words: Al-Cu-Mg alloy; rapid cold stamping; nanoprecipitate; fracture behavior; breaking mechanism