Extraordinary simultaneous enhancement of the coercivity and remanence of dual alloy HRE‐free Nd‐Fe‐B sintered magnets by post‐sinter annealing

•Both the remanence and coercivity are improved after the 2nd annealing process.•The coercivity is hugely increased from 10.09 kOe for the as-sintered sample to 17.19 kOe for the 2nd annealed magnet, with a significant increment of 70.37%.•The matrix grains are enveloped by a (Pr,Nd,Cu,Ga)-enriched layer after the 2nd annealing process.•HRE-free Nd-Fe-B sintered magnets with excellent comprehensive magnetic properties were manufactured by Pr-Fe-Ga boundary addition.