| The Mg₂Si precipitates in A356 alloy have been characterized by high resolution transmission electron microscopy with the combined use of a computer-aided image processing system. We observed that G.P.zones, β$quot;, β`, and B` phases aged at 155℃, 175℃, 195℃ and 250℃, respectively. It was found that the orientation relationship between the precipitates and the matrix. The β$quot; phase has a monoclinic structure. The crystallographic orientation relationship is found as follows : (001)_(Al) // (010)_(β$quot;), [3￣10]_(Al) // [001]_(β$quot;), [230]_(Al) // [100]_(β$quot;) and β◎105°. The β` phase has two types of the crystal structure; the hexagonal structure with the lattice parameter a = 0.704 ㎚ and the orthorhombic structure with lattice parameters a = 0.734 ㎚, b = 0.658 ㎚ and c = 0.405 ㎚. The B` phase has a hexagonal structure. The angle between the rod direction of B` phase and the [010] direction of the matrix is 10°. |
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