Morphology of Dispersoids in an Annealed Al-Mg Alloys

Morphology of dispersoids in an annealed Al-Mg alloy were investigated using TEM. Five kinds of dispersoids with different structures and morphologies were observed in an annealed Al-Mg alloy. The 1st, or spherical-like one is monoclinic structured θ-Al 45 (Mn,Cr) 7 phase with twin and orientation domain. The 2nd or plate-shaped one is η-Al 5 (Mn,Cr) phase with monoclinic or pesuo-tetragonal structure. The 3rd or prismatic-like one is a new hexagonal structured Al 6.4 Mn phase with a unit cell of a =1.72nm, c =1.27nm, and γ =120°, and the 4th or big rod-shaped one is orthorhombic structured Al 6 (Mn,Fe) phase which is often reported. The 5th one is E-Al 18 Mg 3 (Mn–Cr) 2 phase with twin or triple twin observed occasionally in Al-Mg annealed alloy. The first two of dispersoids are in majority, followed by the middle two and a small number of the fifth. Formation mechanisms of these particles in Al-Mg alloy are discussed according to phase diagram and possible formation of the twins in the particles are described based on minimum energy.