Microstructure and Mechanical Properties of AZ91 Magnesium Cup Processed by a Combined Backward Extrusion and Constrained Ironing Method

Subject Areas : Mechanical Engineering

M.  Khodsetan ¹ (Department of Mechanical Engineering, University of Tehran, Iran)
Ghader  Faraji ² (Department of Mechanical Engineering, University of Tehran, Iran)
V.  Tavakkoli ³ (Department of Mechanical Engineering, University of Tehran, Iran)
K.  Abrinia ⁴ (Department of Mechanical Engineering, University of Tehran, Iran)

Received: 2016-06-21 Accepted : 2016-08-07 Published : 2017-03-01

Keywords: Thin-walled cup, AZ91, Constrained ironing, Thickness reduction ratio, Backward extrusion,

Abstract :

A combined metal forming process consisted of backward extrusion (BE) and constrained ironing (CI) is used to produce thin walled ultrafine grained (UFG) magnesium cups. In this new method, the initial thick-walled cup is formed from the bulk material using the BE process and then the CI process is used to produce a UFG thin-walled cups. The advantage of the CI process is applying compressive stresses that are suitable to form hard to deform materials like magnesium alloys without fracture while achieving higher thickness reduction ratio (TRR). The results showed that after this new combined method, the tensile strength raised to 233 MPa, from the initial values of 123 MPa. Simultaneous improvement in strength and ductility attributes to very high hydrostatic compressive stresses and also breakage of Mg17Al12 precipitates in to smaller parts that facilitate the movement of dislocation. Also, the hardness increased to about 233 MPa from the initial values of 58 HV. Significant grain refinement was also taken place and the grain size in the BE+CI sample reduced to ~1 μm from the initial value of ~150 μm due to imposing high value of strain. This combined method is very promising for processing of UFG thin-walled cup-shaped samples from hard to deform materials. SEM images illustrated the brittle fracture at unprocessed and BE samples with existence of wide crack and shallow-elongated dimples but BE+CI sample revealed brittle fracture with fewer cracks due to hydrostatic pressure.

References:

[1]    Hosseini, S. H., Abrinia, K., and Faraji, G., “Applicability of a modified backward extrusion process on commercially pure aluminum”, Materials & Design, Vol. 65, 2015, pp. 521-528.

[2]    Fatemi-Varzaneh, S. M., Zarei-Hanzaki, A., “Accumulative back extrusion (ABE) processing as a novel bulk deformation method”, Materials Science and Engineering: A, Vol. 504, No. 1, 2009, pp. 413-420.

[3]    Farhoumand, A., Ebrahimi, R., “Analysis of forward–backward-radial extrusion process”, Materials & Design, Vol. 30, No. 6, 2009, pp. 2152-2157.

[4]    Lee, R.-S., Kwan, C. T., “A modified analysis of the backward extrusion of internally circular-shaped tubes from arbitrarily shaped billets by the upper-bound elemental technique”, Journal of Materials Processing Technology, Vol. 59, No. 4, 1996, pp. 351-3581996.

[5]    Kudo, H., “Some analytical and experimental studies of axi-symmetric cold forging and extrusion-I”, International Journal of Mechanical Sciences, Vol. 2, No. 1, 1960, pp. 102-127.

[6]    Avitzur, B., Bishop, E. D., Hahn, J. W. C., “Impact Extrusion-Upper Bound Analysis of the Early Stage”, Journal of Engineering for Industry, Vol. 94, No. 4, 1972, pp. 1079-1086.

[7]    Luo, Z. J., Avitzur, B., “Limitations of the impact extrusion process”, International Journal of Machine Tool Design and Research, Vol. 22, No. 1, 1982, pp. 41-56.

[8]    Faraji, G., Mashhadi, M. M., and Kim, H. S., “Microstructural evolution of UFG magnesium alloy produced by accumulative back extrusion (ABE)”, Materials and Manufacturing Processes, Vol. 27, No. 3, 2012, pp. 267-272.

[9]    Faraji, G., Mashhadi, M., and Kim, H., “Microstructure inhomogeneity in ultra-fine grained bulk AZ91 produced by accumulative back extrusion (ABE)”, Materials Science and Engineering: A, Vol. 528, No. 13, 2011, pp. 4312-4317.

[10] Abdolvand, H., et al., “A novel combined severe plastic deformation method for producing thin-walled ultrafine grained cylindrical tubes”, Materials Letters, Vol. 143, 2015, pp. 167-171.

[11] Faraji, G., et al., “Parallel tubular channel angular pressing (PTCAP) as a new severe plastic deformation method for cylindrical tubes”, Materials Letters, Vol. 77, 2012, pp. 82-85.

[12] Abdolvand, H., et al., “Evaluation of the microstructure and mechanical properties of the ultrafine grained thin-walled tubes processed by severe plastic deformation”, Metals and Materials International, Vol. 21, No. 6, 2015, pp. 1068-1073.

[13] Khodsetan, M., Faraji, G., and Abrinia, K., “A Novel Ironing Process with Extra High Thickness Reduction: Constrained Ironing”, Materials and Manufacturing Processes, Vol. 30, No. 11, 2015: p. 1324-1328.

[14] Faraji, G., et al., “Mechanical and Microstructural Properties of Ultrafine Grained AZ91 Magnesium Alloy Tubes Processed via Multi Pass Tubular Channel Angular Pressing (TCAP)”, Journal of Materials Science & Technology, Vol. 30, No. 2, 2013, pp. 134-138.

[15] Faraji, G., Mashhadi, M. M., and Kim, H. S., “Microstructure inhomogeneity in ultra-fine grained bulk AZ91 produced by accumulative back extrusion (ABE)”, Materials Science and Engineering: A, Vol. 528, No. 13-14, 2011, pp. 4312-4317.

[16] Gau, J. T., et al., “Using micro deep drawing with ironing stages to form stainless steel 304 micro cups”, Journal of Manufacturing Processes, Vol. 15, No. 2, 2011, pp. 298-305.

[17] Agnew, S. R., Duygulu, Ö., “Plastic anisotropy and the role of non-basal slip in magnesium alloy AZ31B”, International Journal of Plasticity, Vol. 21, No. 6, 2005, pp. 1161-1193.

[18] Fatemi-Varzaneh, S. M., Zarei-Hanzaki, A., and Beladi, H., “Dynamic recrystallization in AZ31 magnesium alloy”, Materials Science and Engineering: A, Vol. 456, No. 1, 2007, pp. 52-57.

[19] Xing, J. X. Y., Miura, H., and Sakai, T., “Mechanical Properties of Magnesium Alloy AZ31 after Severe Plastic Deformation”, Materials Transactions, Vol. 4, No. 2, 2008, pp. 69-75.

[20] Tan, J. C., Tan, M. J., “Dynamic continuous recrystallization characteristics in two stage deformation of Mg–3Al–1Zn alloy sheet”, Materials Science and Engineering: A, Vol. 339, No. 1, 2003, pp. 124-132.

[21] Faraji, G., Mashhadi, M. M., and Kim, H. S., “Tubular channel angular pressing (TCAP) as a novel severe plastic deformation method for cylindrical tubes”, Materials Letters, Vol. 65, No. 19, 2011, pp. 3009-3012. 2011.

[22] Reshadi, F., et al., “Deformation speed and temperature effects on magnesium AZ91 during tubular channel angular pressing”, Materials Science and Technology, Vol. 31, No. 15, 2015, pp. 1879-1885.

[23] Afrasiab, M., et al., “The Effects of the Multi-pass Parallel Tubular Channel Angular Pressing on the Microstructure and Mechanical Properties of the Cu–Zn Tubes”, Transactions of the Indian Institute of Metals, Vol. 68, No. 5, 2015, pp. 873-879.

[24] Chen, Y., et al., “Effects of extrusion ratio on the microstructure and mechanical properties of AZ31 Mg alloy”, Journal of Materials Processing Technology, Vol. 182, No. 1-3, 2007, pp. 281-285.

[25] Tavakkoli, V., et al., “Severe mechanical anisotropy of high-strength ultrafine grained Cu–Zn tubes processed by parallel tubular channel angular pressing (PTCAP)”, Materials Science and Engineering: A, Vol. 625, 2015, pp. 50-55. 2015.