Microstructure characteristics of Cu–Mn alloys during laser surface remelting

Laser surface remelting experiments were conducted on Cu–26.6, 27.3 and 31.4 wt.% Mn alloys to investigate their microstructure evolution and growth rate under an ultra-high temperature gradient. The experimental results showed that the microstructure of Cu–26.6 wt.% Mn alloy changed from cell to dendrite, super-fine cell and segregation-free solid with increase of growth rate. No dendrite growth appeared in the whole range of growth rate for Cu–27.3 wt.% Mn and Cu–31.4 wt.% Mn alloys which fully grew in cellular form. The elongated cellular structure appeared before high-velocity absolute stability was reached in Cu–31.4% Mn alloy, which showed a symmetric behavior in the morphological transformation in both limits of the absolute stability and the low rate interface morphological stability. The critical rates of absolute stability for Cu–31.4, 27.3 and 26.6 wt.% Mn alloys were 113.3, 212.6 and 260.5 mm/s, respectively, which was in reasonable agreement with those predicted by M–S theory.