Phase transition (FCC→BCC) improves magnetic and mechanical properties of HEAs. Ms of FCC + BCC duplex-phase HEAs abnormally increases with additions of Cu and Al. Ms, σ0.2 and hardness of FeCoNi(CuAl)0.8 HEAs remarkably increase after annealing. TEM shows Cu-rich precipitates disperse in BCC matrix of FeCoNi(CuAl)0.8 HEA.