A comparative study on microstructure and damping capacity of Mn-Cu based alloys with dendrite and equiaxial grain

A 70Mn-24.95Cu-3Al-2Zn-0.05Ce (at.%) alloy was prepared by vacuum induction melting (VIM) technblogy. Part of the alloy was further hot rolled and annealed (HRA) respectively at 500 degrees C with a thickness reduction of 50% and 850 degrees C for 5 h. Then, VIM and HRA samples were aged at 430 degrees C for 2-4 h. The comparative study on microstructure and damping capacity of VIM and HRA alloys has been conducted. The results show that the microstructure of VIM alloy comprises gamma-MnCu dendrites with obvious compositional segregation while that of HRA alloy primarily consists of equiaxial gamma-MnCu grains. Some alpha-Mn particles are formed in HRA alloy aged for 4 h. The dendritic segregation has no obvious effect on starting fcc-fct transformation temperature of the alloys. The VIM alloy has larger tetragonal distortion 1-c/a than HRA one. Two stepped fcc-fct phase transformation occurs and couples to promote the formation of a high and wide phase transformation damping platform in VIM alloy especially aged for 4 h compared to a phase transformation damping peak in HRA one. There is a significantly towering twin relaxation internal frication peak in VIM alloy especially aged for 2 h compared to HRA one.