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- 저자 : M. Baniassadi (검색결과 1 건)
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M. Eftekhari,G. Faraji,M. Bahrami,M. Baniassadi 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.7
In this study, hydrostatic cyclic extrusion compression (HTCEC) is introduced as a novel severe plastic deformation techniquefor producing the relatively long and large ultrafine grained (UFG) and nano-grained tubes. In HTCEC technique, the utilizationof pressurized hydraulic fluid between the piece and the die leads to the reduction of the friction force and the requiredprocessing load. All of these conditions facilitate the processing of the long and large tubes. Also, during HTCEC process,a movable mandrel is placed inside the hollow tube, which plays a main role in the reduction of the required hydrostaticpressure. To investigate the efficiencies of HTCEC process, aluminum 5052 alloy tubes were processed by HTCEC up totwo passes. Then, the mechanical properties and microstructure evolution were examined. After the first pass of HTCEC,tangled and diffused arrangements of dislocations were formed. Then, the second pass of HTCEC resulted in a more refinedand more homogeneous UFG microstructure with an average subgrain size of 636 nm, while the average grain size of theinitial sample was ~ 360 μm. Tensile tests and hardness measurements revealed that two passes of HTCEC led to an increasein the yield strength from 98 MPa to 254 MPa (~ 2.6 times higher), the ultimate strength from 178 MPa to 306 MPa (~ 1.72times higher) and the microhardness from ~ 56 to ~ 120 Hv (~ 2.14 times higher). Simultaneously, a decrease in the elongationto failure from 31.6 to 15.4% was observed, which is a small amount compared to the results of other studies. Also, incomparison to one-pass, a more homogeneous microhardness distribution through the thickness was detected in the two-passprocessed tube. Fractography evaluations by SEM indicated that predominantly ductile fracture occurred in all samples. Furthermore, the equivalent strain and the pressing load of HTCEC process was evaluated by FEM simulation. It seems thatHTCEC process, by utilizing its potentials, can produce the relatively long and large UFG tubes having a simultaneous highstrength and good ductility.
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