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Vol.37, No.12, 1458 ~ 1462, 1999

Title

Microstructure of Twin Related Silicon Crystals in a Cast Al-Si(A356) Alloy

조종우Jong Woo Cho,이영호Young Ho Lee,이갑호Kap Ho Lee

Abstract

The microstructure of twin related silicon crystal in a cast Al-Si-Mg(A 356) alloy was investigated by electron microscopy. Two kinds of eutectic silicon crystals with different size are observed in the alloy quenched from 535℃. Stacking faults and micro-single twins are observed in the eutectic silicon crystals larger than 2㎛ in diameter. The multiple twins grown by the twin-plane re-entrant edge(TPRE) mechanism based on {111} twinning with <211> growth direction are observed in fine eutectic silicon crystals. The {111} planes meet at the twin plane to form three re-entrant angles of 141°, each with a matching ridge on the opposite side. Specially, the five-fold twinned eutectic silicon crystal containg five twin planes with a common <110> axis is observed. The silicon crystals, which are different from eutectic silicon crystal, are precipitated with the definite crystallographic relationship of <001>_(Al) ∥ <110>_(si) in the alloy aged at 175℃. The special crystallographic relationship and interfaces are interpreted by matching silicon and aluminum lattice spacing.

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