In the current study, a novel severe plastic deformation (SPD) technique entitled cyclic extrusion channel angular pressing (CECAP) is proposed appropriate for producing ultrafine grained cylindrical material. In this new method, cyclic extrusion compression (CEC) and equal channel angular pressing (ECAP) processes are combined which solves drawbacks of both processes.Advantageous of the new process may be considered in two views of points of processing and properties. This new process increases the hydrostatic compressive stress of ECAP as well as shear to the total strain of CEC. Also, CECAP solves needing back pressure problem of CEC process which is an important feature of the new process. The process treated an AZ91 alloy and remarkable grain refinement and significant improvement in strength, ductility and hardness were achieved because of higher hydrostatic compressive stresses.
A combination of parallel tubular channel angular pressing (PTCAP) and tube backward extrusion (TBE) as a novel combined severe plastic deformation (SPD) was applied on AZ91 alloy to produce ultrafine-grained (UFG) thinwalled tubes. The effects of combined SPD process were investigated on the microstructure refinement and mechanical properties. Also, hydro-bulge test was carried out to reveal the mechanical properties. The results showed a notable increase in ultimate strength, yield strength and microhardness of the thin-walled UFG tube were achieved compared to that from PTCAP process. A remarkable grain refinement achieved. Applying three-passes-combined process refine the grain size to 8.8 μm from an initial value of ∼150 μm. For one pass-and two passes-processed thin-walled tubes, it was about 12.4 and 9.8 μm, respectively. Yield and ultimate strengths were increased notably to 150 and 354 MPa for 2P+TBE tube, from the initial values of 86 and 166 MPa, respectively. The maximum microhardness was increased to about 105 Hv for the 2P+TBE tube from the initial value of 56 Hv. Hydro-bulge test showed that the bursting pressure increased to 246 bar for 2 passes-thin-walled tube from the initial value of 160 bar. It was 220 and 195 bar for 1 pass-and 3 passes-thin-walled tubes, respectively.
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