Effect of combined addition of Zr, Ti and Y on microstructure and tensile properties of an Al-Zn-Mg-Cu alloy

Composite micro-alloying is an important technique for developing cost-effective, high-performance aluminum alloys. Here, the effect of combined addition of Zr, Ti and rare-earth Y on the microstructure and tensile properties of an Al-7.6Zn-1.6 Mg-2.1Cu (wt.%) alloy is systematically investigated by means of X-ray diffraction, optical microscopy, scanning electron microscopy, transmission electron microscopy and room-temperature unixal tensile tests. After adding 0.12 %Zr, 0.04 %Ti and 0.28 %Y, L1(2)-Al3Zr/(Al,Zn)(3)Zr, AlMgZnTiCuFe and (Al,Zn)(8)Cu4Y phases were induced; the as-T6 treated microstructure of the base alloy changed from fully recrystallized to fully unrecrystallized, accompanied by strong < 100 > + < 111 > fiber textures along extrusion direction. As a result, the Al-Zn-Mg-Cu-Zr-Ti-Y alloy with low Zn and Mg contents exhibits an ultimate tensile strength of 692 MPa, yield strength of 647 MPa (similar to 36 % higher than the base alloy) and 6.8 % elongation. The main strengthening mechanisms responsible for this high yield strength are Orowan dislocation bypassing strengthening (similar to 449 MPa), fiber texture strengthening, and dispersion strengthening. Moreover, the synergistic strengthening effect of rare-earth Y and transitional element(s) Zr and/or Ti was revealed, which may be related to the formation(s) of nanoscale networkstructured Al8Cu4Y and/or L1(2)-Al-3(Zr,Y) phase(s). The massive formation of the Al8Cu4Y network structure requires a narrow process window. (C) 2022 The Author(s). Published by Elsevier Ltd.