Al-Zn-Mg-Cu合金の再結晶挙動に及ぼすZr添加とCr添加の差

抄録

Recrystallized structures of 7xxx series aluminum alloys were examined paying attention to the difference of the effects between Zr and Cr additions. The Al-5.7%Zn-2.5%Mg-1.5%Cu alloys with 0.1%Zr or 0.2%Cr were mainly used as specimens. They were hot-rolled, solution-treated, cold-rolled and then subjected to recrystallization-heat-treatment (RHT) at temperatures ranging from 673 to 798 K. Growth rate of sub-grains at an early stage of RHT is greater in Zr-bearing alloy than in Cr-bearing alloy. Recrystallization occuring successively in the region having sub-grain structures is generally suppressed in Zr-bearing alloy, leading to the decreased fraction of recrystallized area. The fraction of recrystallized area and the recrystallized grain size become larger in Zr-bearing alloy, when RHT temperature increases. Because, coarsening of Al₃Zr particles is caused. The grain size in longitudinal direction in Cr-bearing alloy decreses at elevated RHT temperatures. These results of microstructural observations are almost the same in commercially available 7050 and 7075 alloys.