Al-Mg-Zn 3元系耐熱合金の析出に及ぼす第4元素添加の影響

抄録

In the present study, we investigated the effects of Cu or Ni additions on the precipitation of intermetallic phases in the heat-resistant aluminum alloy with a ternary composition of Al-5Mg-3.5Zn (mol%). The quaternary alloys with 1 mol%Cu or 1 mol%Ni content were solution-treated at 480 °C and subsequently aged at 300 °C for different periods. Both Cu and Ni additions have a slight effect on the age-hardening of these alloys at 300 °C. The added Cu element partitioned into not only T-Al₆Mg₁₁Zn₁₁ phase but η-Zn₂Mg phase precipitated in the α-Al matrix. The observed Cu enrichment in the precipitates of T phase indicated high stability of T phase in the Al-Mg-Zn-Cu quaternary system, which was different from the results of thermodynamic calculations using the existing database. The added Ni element enhanced the formation of fine Al₃Ni phase located at grain boundaries and slightly influenced the precipitation of T phase in grain interior. These results provided new insights to design novel heat-resistant Al alloys using the Al-Mg-Zn-Cu-Ni system.