Dynamic impact behavior of 2219 aluminum alloy with mixed grain structure

Abstract

Optical microscopy, electron backscatter diffraction and transmission electron microscopy were used to examine the grain structure and precipitation changes in a 2219 aluminum alloy with mixed grain structure before and after dynamic impact. The intergranular deformation coordination and strengthening mechanisms are discussed. The average Schmid factor after impact is 0.453 to 0.462, which is close to the value prior to deformation. This stability arises as grain refinement after impact enhances the intergranular deformation coordination, while retained coarse grains provide dislocation accommodation. These effects offset deformation resistance induced by strain hardening. As strain rate increases, the thickness of the precipitates first increases and then decreases, while the number density exhibits the reverse trend. Dislocation density consistently increases with strain rate; the orientation density of texture aligned with the loading direction also increases, except in the adiabatic shear band region of 7329 s⁻¹ impacted specimen, where it decreases. Both flow stress during impact and hardness after impact increase with strain rate. The strengthening mechanisms are solid solution, precipitation, dislocation, grain boundary, and texture strengthening, with precipitation and dislocation strengthening being the most significant. Precipitation strengthening contributes approximately 30 % to the yield strength, and dislocation strengthening over 45 %. Solid solution and grain boundary strengthening contribute approximately 10 % and 8.5 %, respectively. Texture strengthening has a smaller contribution that initially increases and then slightly decreases with increasing strain rate.