断熱鋳型式連続鋳造法で作製した鍛造用 Al-Si 系合金の組織と高温強度に及ぼす銅濃度の影響

Al-Si alloy billets with 0, 2, 4, and 6 mass%Cu have been fabricated by the Heat-Insulating-Mold method. The microstructures and high-temperature mechanical properties at 423 K, 523 K, and 623 K have been investigated. Increasing Cu concentration changed the types of constituent particles and increased their area fraction. 0.2% proof stress (σ_0.2) and ultimate tensile strength (σ_UTS) increased with increasing Cu concentration at each temperature. SEM observation showed that precipitates increased with increasing Cu concentration and remained in the matrix below 523 K but dissolved into the Al matrix at 623 K. The former suggested that the precipitates contributed to the strength below 523 K. On the other hand, significant work-hardening was confirmed until 0.2% strain at 623 K, which suggested that the constituent particles contributed to the strength just like particle-reinforced composites. The work-hardening rate and the amount of work-hardening increased with increasing Cu concentration and correlated with the interparticle spacing of the constituent particles. It indicated that decreasing interparticle spacing enhanced constraining matrix deformation, and it led to an increase of σ_0.2