Heterogeneous precipitation during homogenization cooling in Al–Mg–Si alloys

“Boundaries” are frequently observed within the grains during homogenization/solution cooling of Al-Mg-Si billets. In this work, we confirmed that the formation of the “boundaries” is due to a complex but interesting heterogeneous precipitation behavior. This heterogeneous precipitation contains a high temperature behavior and a low temperature behavior, which is rarely observed during aging treatment with deformation induced dislocations. During the high temperature stage of cooling (>350 °C), the rod/lath-like precipitates formed at the dislocations tend to grow along two or three 〈1 0 0〉_Al directions, however, as the temperature decreases to near 200 °C, the precipitates tend to line up and parallel to each other, and the string-like precipitates appear along the dislocations between the precipitates.