Structures and tensile properties of Sc-containing 1445 Al-Li alloy sheet

The strength and precipitates after T8-aging (second-step aging at 170 °C following first-step aging at 150 °C for 4 h after 6% predeformation) and grain structures of 1445 Al-Li alloy (Al-1.7Li-1.5Cu-0.9Mg-0.1Mn-0.1Zr-0.1Ag-0.1Ti-0.08Sc-0.07Ni) cold-rolled sheet were investigated. The main precipitates are δ′ (Al3Li) and S′ (Al2CuMg). It is critical that nano-sized Al3(Sc,Zr) dispersoids are formed, and the Cu-enriched and Sc-containing W phases (AlCuSc) are not found. Due to the strong pinning effect of the nano-sized Al3(Sc,Zr) dispersoids on sub-grain boundaries and dislocations, the solutionized 1445 Al-Li alloy sheet displays non-recrystallization characteristics, which corresponds to a high volume fraction of deformation textures of Copper {112}<111>, Brass {011}<211> and S {123}<634>. This non-recrystallization feature makes the 1445 Al-Li alloy suitable for thin sheet. In addition, due to the addition of minor Ni, Al9FeNi particles instead of Al7Cu2Fe particles are formed.