Cyclic flaring and sinking (CFS) as a new severe plastic deformation method for thin-walled cylindrical tubes

In this research, a novel severe plastic deformation (SPD) method entitled cyclic flaring and sinking (CFS) is presented for producing of the ultrafine-grained (UFG) thin-walled cylindrical tubes. Finite element (FE) results showed that CFS process has a good strain homogeneity and requiring a low load. CFS process includes two different flaring and sinking half-cycles. At flaring half cycle, the flaring punch with two stepped regions is pressed into the tube. Shear and normal tensile strains are applied as a result of the existence of shear zones and increase in the tube diameter. In the second half cycle, the tube is then pressed to sinking die that applies same shear strains and normal compression strain so that the initial diameter of the tube is achieved and high plastic strain is applied. This process can be run periodically on the tube to exert more strain and consequently finer grain size and ultimately achieve better mechanical properties. The results indicated that the yield and ultimate strengths of the CFS processed Al (1050) tube were significantly increased to 165 MPa, and 173 MPa, respectively from the initial values of 50 MPa, and 115 MPa. The elongation to failure was decreased to about 14% after three cycles from the initial value of 42%. In addition, the hardness increases to ~38 Hv after ten cycles of CFS from ~23 Hv.