Effect of grain boundaries on the distribution of θ′ precipitates in Al–2Cu alloy bicrystals during stress ageing

Grain boundaries provide extra energy field to supply nucleation and growth of θ′precipitate during stress ageing, and influence the distribution of precipitates variants. The effect of grain boundaries on the distribution of two θ′ precipitates variants (010) and (001) were investigated in Al–2Cu alloys bicrystals during stress ageing. The hardness differences due to the various distribution of precipitates along the bicrystal samples were also studied. The results of transmission electron microscopy (TEM) observation showed that the grain boundary of bicrystal inhibited the stress-orienting effect on precipitates, which appears in stress-aged single crystal. (010) and (001) variants of θ′ precipitates have the same fraction in area near the grain boundary and have the same density as in single crystal areas. Hardness difference between the area near grain boundaries and the single crystal area is smaller in stress-aged sample compared to the free stress aged sample. Which means the anisotropy of strength contribution of two θ′ variants were reduced because of grain boundaries. The results of this research provide insight into solving the anisotropy problem during stress ageing by introduce more grain boundaries in the manufacture of Al–Cu alloys.