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.