Effect of specimen surface state on microstructure and mechanical properties of linear friction welded joint

In this paper,for TC4 titanium alloy commonly used in aircraft components,effect of three states of wire-electrode cutting,rough milling surface and grinding surface before welding on formability,microstructure,oxygen element distribution and mechanical properties of linear friction welded joint were studied,respectively. Results showed that joints in three states were well formed. The macrostructure after welding included base metal（BM）,thermal mechanical affected zone（TMAZ） and weld zone（WZ）. Grains of TMAZ was elongated along the direction of the force and α phase dissolved. Dynamic recrystallization occurred in WZ,and fine lamellar microstructure was formed inside the grains. The content of oxygen element in the joint of wire cutting and rough milling states did not increase significantly,which was similar to that in the joint of grinding state. Joints in the three states before welding had equal tensile properties. Under conditions of K_t= 1,R= 0. 06,550 MPa,Joints in the three states had equal fatigue life.