Effect of grain boundary on the precipitation behavior and hardness of Al-Cu-Mg alloy bicrystals during stress-aging

While it is clear that precipitates near grain boundaries in aluminum alloys nucleate more easily and grow more quickly, the mechanism of how the grain boundaries influence the anisotropic distribution of S precipitates is still unknown. In this study, a bicrystal Al-Cu-Mg alloy specimen was prepared to obtain a single grain boundary. The precipitation distribution and hardness of the Al-Cu-Mg alloy bicrystal were analyzed after stress aging at 30 MPa. Transmission electron microscopy was used to analyze the precipitation behavior of S precipitates, and the hardness was tested along the location on the bicrystal specimen. The hardness of the right area around the grain boundary is lower than that of the left area around the grain boundary after stress aging. The precipitation behavior around the grain boundary is different from that in the matrix. For the left area near the grain boundary with the (1, −1, 8)Al plane orientation, the anisotropic distribution of the S precipitates is inhibited. For the right area near the grain boundary with the (3, 5, 6)Al plane orientation, the anisotropic distribution of the S precipitates is even more pronounced than that in the right matrix. This difference in the influence depends on the crystallographic orientations of the matrix around the two sides of the grain boundary.