EFFECT OF PREHEAT TEMPERATURE ON THE ORIENTATION RELATIONSHIP OF (MN,FE)AL-6 PRECIPITATES IN AN AA-5182 ALUMINUM-MAGNESIUM ALLOY

The precipitation of the (Mn,Fe)Al-6 phase during preheating of a commercial AA 5182 Al-Mg alloy was studied by means of scanning electron microscopy, transmission electron microscopy and selected area electron diffraction. The existence of two different morphologies with low and high aspect ratio (called here rhomboidal and platelike) was confirmed. The influence of preheating parameters on the precipitation was found to be close to the one known for Al-Mn alloys. It was found that the platelike dispersoids bear orientation relationships with the matrix of type [100](m) parallel to[(2) over bar 10](pp) and (0(1) over bar1$)(m) parallel to(001)(pp), which are not yet reported in the literature. On the other hand it was shown that rhomboidal precipitates do not follow any orientation relationship with the matrix. The more harmful influence on recrystallization and hot ductility of the rhomboidal precipitates compared to the platelike ones is discussed.