“Branched” structural transformation of the L12-Al3Zr phase manipulated by Cu substitution/segregation in the Al-Cu-Zr alloy system

•Cu induces a “branched” path for the structural transformation of L12-Al3Zr phase.•Cu addition increases the energy barrier for APB activation by ≈ 50%, increasing the thermal stability of the L12 phase.•Cu atoms may preferentially segregate at the Al-Zr layer adjacent to the APB, promoting a transformation to a new phase, termed as Al4CuZr.