Orientation relationship between Al₆Mn precipitates and the Al matrix during continuous recrystallization in Al-1.3%Mn

Annealing of cold-rolled supersaturated Al-1.3 wt% Mn leads to heavy precipitation of fine particles on the as-deformed microstructure. Depending on the crystallographic orientation of the deformed matrix grains, particles with different morphologies, namely spherical, rhomboidal and plate-like, have been observed. This variation in morphology could be traced back to differences in local misorientation caused by different dislocation substructures in different matrix orientations. Microstructural investigations and selected-area diffraction (SAD) analysis in a transmission electron microscopy (TEM) study were employed to characterize the various particles and to determine their orientation relationship to the Al matrix. Independent of the particle morphology, most Mn precipitates were identified as Al₆Mn; only occasionally was Al₁₂Mn observed. Upon consideration of the various crystal symmetries, two different orientation relationships were discerned, which can be written as (110)_m||(111)_p, [001]_m||[211]_p and (110)_m||(111)_p, [112]_m||[121]_p. These orientation relationships are discussed with respect to the existence of several low misfits of lattice spacings and compared to literature data.