The orientation relationships of nanobelt-like Si₂Hf precipitates in an Al–Si–Mg–Hf alloy

The orientation relationships (ORs) between the Al matrix and Si₂Hf precipitates with an orthorhombic structure in an Al–Si–Mg–Hf alloy after heat treatment at 833 K for 20 h were investigated by transmission electron microscopy and electron diffraction. Four ORs are identified as (100)_Al||(010)_p, (01)_Al||(101)_p and [011]_Al||[01]_p; (11)_Al||(010)_p and [011]_Al||[01]_p; (12)_Al||(010)_p, (101)_Al||(100)_p and [1]_Al||[001]_p; (1)_Al||(010)_p and [112]_Al||[01]_p. The habit planes of these four ORs are rationalized by the fraction of good atomic matching sites at the interface. In addition, the formation of Si₂Hf precipitates with a nanobelt-like morphology is interpreted on the basis of the near-coincident site lattice distribution.