Nucleation and growth crystallography of Al8Mn5 on B2-Al(Mn,Fe) in AZ91 magnesium alloys

作者：Zeng G^*; Xian J W; Gourlay C M^*

来源：Acta Materialia, 2018, 153: 364-376.

DOI：10.1016/j.actamat.2018.04.032

• Electron backscatter diffraction
• Intermetallics
• Crystal growth

Manganese is widely added to Mg-Al-based alloys to form Al-(Mn,Fe) intermetallics that combat impurity Fe. Here EBSD, deep etching and FIB-tomography are combined to study the nucleation and growth crystallography of Al-Mn-Fe particles in Mg-9Al-0.7Zn-0.15Mn-0.002Fe (wt%) solidified at 1 K.s(-1). It is shown that Al8Mn5 nucleates on B2-Al(Mn,Fe) particles and an incomplete peritectic transformation results in a Fe-richer B2-Al(Mn,Fe) core enveloped by a low-Fe Al8Mn5 shell. A reproducible orientation relationship (OR) is measured, and the close lattice match and OR are discussed in terms of the group-subgroup relationship between these phases. It is found that most rhombohedral Al8Mn5 particles are twinned, consisting of four orientations related by -90 degrees rotations around three common < 1<(1)over bar>02 >, which is discussed in terms of the pseudo-cubic <100> axes of the Al8Mn5 rhombohedral gamma brass. Al8Mn5 grew as equiaxed particles that are explained by polyhedron models based on {100}, {110} and {112} facets of the pseudo-cubic Al8Mn5 cell. The results indicate that, at low Fe:Mn ratio, most impurity Fe is dissolved in B2 particles that are encapsulated by low-Fe Al8Mn5 which may be important for corrosion resistance.

• 出版日期2018-7