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Processing of commercially pure copper tubes by hydrostatic tube cyclic extrusion–compression (HTCEC) as a new SPD method

Eftekhari M., Faraji G., Bahrami M.

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 3

595--606

EN

In this study, severe plastic deformation (SPD) process of hydrostatic tube cyclic extrusion–compression (HTCEC) was performed through two passes on the commercially pure copper tubes with the purpose of fabricating relatively long ultrafine-grained (UFG) tubes. In HTCEC process, the presence of pressurized hydraulic fluid around the piece plays a key role in the reduction of the friction load and, consequently, in the reduction of required pressing load. In principle, this facilitates the production of long and large tubes. After processing by HTCEC, the mechanical characteristics and microstructure evolution were examined. Microstructure analysis revealed that after the first pass of HTCEC process, an ultrafine cell microstructure with an average size of ~ 993 nm was attained. After two passes of HTCEC, the average size of cells/subgrains was reduced to ~ 340 nm. This was while the average grain size of the annealed sample was 41 μm. Also, after two passes of HTCEC process, a remarkable increase in the yield strength from 154 to 336 MPa, and the ultimate strength from 223 to 414 MPa was observed. Furthermore, the mean value of microhardness increased from 74 to 149 HV, and a more uniform distribution of microhardness along the thickness was seen, compared to the first pass of HTCEC. Meanwhile, unlike most conventional SPD methods, the value of elongation to failure was slightly lessened from 59.5 to 41.6%. SEM fractography analysis denoted that mostly ductile fracture occurred in the HTCEC-processed samples. In general, two main advantages of HTCEC process can be the production of relatively long ultrafine-grained tubes and the significant increase in the strength and hardness besides a low loss of ductility.

2

Mechanical Properties and Microstructure of WE43 Mg Alloy Processed by Warm ECAP Followed by Extrusion

Torkian A., Faraji G., Karimpour M.

Archives of Metallurgy and Materials

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2018

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Vol. 63, iss. 3

1093--1100

EN

In the present paper, the effects of the subsequent extrusion after multi-pass equal-channel angular pressing (ECAP) process on the mechanical properties and microstructure of WE43 magnesium alloy are investigated. First, second and fourth passes ECAP followed by an extrusion process are applied on WE43 magnesium alloy to refine the microstructure and to improve the mechanical properties for biomedical applications. The results showed that among the ECAPed samples, the highest and lowest strength were obtained in the second and the first pass processed samples, respectively. The four passes processed sample showe d the highest elongation to failure with moderate strength. The sample processed via first pass ECAP followed by extrusion exhibi ts an excellent combination of ductility and strength. The highest strength was obtained in the sample processed via the second pa ss ECAP followed by extrusion while the highest elongation was achieved in the sample processed via fourth pass ECAP followed by extrusion. Moreover, Vickers micro-indentation tests demonstrate that hardness is enhanced by an increase in the number of ECAP passes. Furthermore, a grain refinement process is presented for ECAP processing of WE43 alloy which shows a good agreement with microstructural investigations.

3

Hot deformation behavior of Mg-Zn-Al alloy tube processed by severe plastic deformation

Fata A., Faraji G., Mashhadi M. M., Tavakkoli V.

Archives of Metallurgy and Materials

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2017

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Vol. 62, iss. 1

159--166

EN

In the current study, severe plastic deformation (SPD) was applied on a commercial Mg-3Al-1Zn alloy tubes via parallel tubular channel angular pressing (PTCAP) route. Different passes of PTCAP process were applied, and microstructure, hardness and tensile properties at the room, and elevated temperatures were evaluated. The results showed that bimodal microstructure appeared and led to AZ31 alloy represented higher hardness, higher strength with a reasonable elongation at room temperature. Similarly, very high elongation to failure was achieved at a higher temperature. The increase in the number of SPD passes up to two, leads to increasing the ductility up to 263% at 400°C. Then, an increase in the number of PTCAP passes to three, leads to decrease in the ductility as the results of formation of microvoids when SPD processing at higher equivalent strains without a sufficient hydrostatic compressive stress. Relatively ductile fracture mode was also occurred in all samples.