Microstructure characterization in a sensitized Al-Mg-Mn-Zn alloy

Alloying elements, present in the aluminum solid solution or the precipitates, influence the corrosion resistance of Al-Mg-Mn-Zn alloys. In this study, sensitizing treatment was applied to an Al-Mg-Mn-Zn alloy to modify the precipitation at the grain boundaries or in the grains. Transmission electron microscopy (TEM) and scanning electron microscope (SEM) were used to characterize various second-phase particles and determine their orientation relationship with the Al matrix. After sensitizing treatment, tau-phase (Mg-32(Al, Zn)(49)) is observed to precipitate along the grain boundaries in a coarser size, producing a discontinuous grain boundary precipitate structure. In addition, Mn-rich particles are found to form with various shapes, such as global, plate and rhombus.