Achieving high superplasticity of a traditional thermal–mechanical processed non-superplastic Al–Zn–Mg alloy sheet by low Sc additions

•The superplastic of the Al–Zn–Mg–Sc–Zr alloy subjected to a traditional thermal–mechanical processing was investigated.•The boundary characteristics and thermal stability of the Al–Zn–Mg–Sc–Zr alloy were examined.•The deformation mechanism for Al–Zn–Mg–Sc–Zr alloy was analyzed.