Optimization of phase composition of Al–Cu–Mn–Zr–Sc alloys for rolled products without requirement for solution treatment and quenching

Abstract

Abstract The possibility to use alloys of the Al–Cu–Mn–Zr–Sc system for obtaining rolled sheets directly from cast ingots (without homogenization process) was investigated. The experimental (SEM, TEM, EMPA, and mechanical tests) study and Thermo-Calc software simulation were used for alloy composition optimization. It was shown that optimal structure could be developed in the alloys of the following compositional range: 1–2% Cu, 1–2% Mn, ∼0.2% Zr and ∼0.1% Sc (wt%). Such nearly single-phase structure achieved in the as-cast state provides high ductility of the alloys and allows for up to 87% hot rolling reduction and up to 75% cold rolling reduction without intermediate annealing. Experimental Al–Cu–Mn–Zr–Sc and commercial AA2219 alloys were compared. Tensile tests of 0.5 mm sheets proved the advantage of the experimental alloy. Although the AA2219 alloy can be considerably hardened upon quenching and aging (T6), this hardening effect completely disappears after short-term heating at 300–350 °C. On the other hand the experimental alloy was thermally stable due to the formation of polygonized structure, which resulted from large amount of Al20Cu2Mn3 and Al3(Zr,Sc) (L12) dispersoids that effectively pinned down dislocations. No secondary Al2Cu precipitates were detected. Such structure is the most favorable for creep resistance as Mn- and Zr-containing dispersoids have a higher thermal stability than Al2Cu precipitates. Proposed range of compositions can be recommended for the development of new aluminum wrought alloys, which will have two main advantages as compared with commercial alloys of the AA2219 type: (1) high tolerance to heating up to 350 °C because of high amount Al3(Zr,Sc) and Al20Cu2Mn dispersoids; (2) energy efficient processing, in particular due to the elimination of homogenization, solution treatment and quenching.