Effect of Mn on the Microstructure and Mechanical Properties of Ti-6Al-4Mo Alloy

In order to develop titanium alloy with high elastic modulus and good comprehensive mechanical properties, Ti-6Al-4Mo-xMn (x=0, 1, 2, 3, 4, wt%) alloys were prepared by a cold crucible suspension melting method. The effect of Mn content on the microstructure and mechanical properties of the alloy was systematically investigated. The results demonstrate that the prepared Ti-6Al-4Mo-xMn alloys are composed of alpha and beta phases without Ti-Mn phase. With the increase of Mn content, the alpha ->beta phase transition temperature decreases, resulting in an increase in volume fraction of beta phase. Moreover, the microstructure of the alloys gradually becomes finer and evolves toward Widmannstatten microstructure. The hardness of the alloy increases from 30 HRC to 46 HRC, and the tensile strength increases from 838 MPa to 1266 MPa, which is attributed to the solution strengthening and microstructure refinement caused by Mn atoms. With the increase of Mn content, the elastic modulus of the alloy increases first and then decreases. When the Mn content is 1wt%, the elastic modulus of the alloy is the highest, which is 136 GPa, and the tensile strength is 916 MPa, which are 24.0% and 3% higher than those of Ti-6Al-4V alloy, respectively.