Effect of Heat Treatments on Microstructure and Mechanical Properties on Electron Beam Welded Joint of Ti650 Alloy

The effects of post-weld heat treatment on the microstructure and mechanical properties of Ti650 alloy electron beam welding (EBW) samples were studied. The results indicate that metastable martensite a' is the main phase in the fusion zone of welding seam. During 700 degrees C/2 h AC heat treatment, a phase transition a'-> a occurs, and a large number of short aciculate secondary a phases are precipitated in the fusion zone. After 1010 degrees C/1.5 h WC+650 degrees C/2 h AC heat treatment, a is obviously coarsened and equiaxed. The microstructure contains the original coarse layer and the secondary short acicular alpha can effectively improve the strength and prevent the crack growth of welded joint. The welded joint has better strength and plasticity under the condition. After subsequent treatment at 700 degrees C/2 h AC, some equiaxed a phases gradually precipitates at the grain boundary, resulting in a decrease in strength and plasticity of the grain boundary. In conclusion, 1010 degrees C/1.5 h WC+650 degrees C/2 h AC is the most suitable post-welding heat treatment for Ti650 EBW welded joint to make the properties of weld and matrix be well matched.