鋳造鍛造アルミニウム合金鋳物の破壊靭性に及ぼすミクロ組織の影響

抄録

Tensile and fracture toughness properties of three typical aluminum casting alloys, A (0.7%Si)–T6, B (4%Si)–T6 and C (7%Si)–T6, were evaluated in both as-cast and as-forged conditions. Cast and forged alloys showed increased elongation and fracture toughness with increase in forging ratio, especially in A (0.7%Si)–T6 alloy. The tensile and yield strengths of cast and forged alloys of B (4%Si)–T6 and C (7%Si)–T6 increased with forging ratio, but decreased in 50% forging ratio. Mechanism of the increased fracture toughness are considered to be a decrease in the size of casting defects with forging ratio. On the other hand, it is also considered to change microstructures of α phase and eutectic Si particle. In the Al–Si–Mg alloys, Mg₂Si is a major precipitate, however, it is considered that the excess Si also contributes to the increase of the strength.