Processing of long ultrafine-grained AM60 magnesium alloy tube by hydrostatic tube cyclic expansion extrusion (HTCEE) un
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ORIGINAL ARTICLE
Processing of long ultrafine-grained AM60 magnesium alloy tube by hydrostatic tube cyclic expansion extrusion (HTCEE) under high fluid pressure F. Samadpour 1 & G. Faraji 1 & M. M. Savarabadi 1 Received: 17 May 2020 / Accepted: 2 November 2020 # Springer-Verlag London Ltd., part of Springer Nature 2020
Abstract In this study, hydrostatic tube cyclic expansion extrusion (HTCEE) at elevated temperatures was utilized to produce relatively long ultrafine-grained (UFG) AM60 magnesium alloy tubes. HTCEE method is able to apply large strains to tubular parts and produce long UFG tubes without changing their dimensions due to the reduction of the friction at interfaces using high-pressure molten polymeric fluid at an elevated temperature. This method is performed on an AM60 magnesium alloy at an elevated temperature of 300 °C, and the microstructure and mechanical properties were examined. The results represent a significant enhancement of the mechanical properties and a dramatic reduction in the grain size. The yield and ultimate strength were increased to 160 MPa and 328 MPa after first passes of HTCEE from the primary values of 130 MPa and 212 MPa; also the elongation to failure increased to 31% from 9%. Microhardness was increased to about 72 Hv after the HTCEE process from the primary value of 50 Hv. Microstructural results showed a significant grain refinement to a grain size of ~ 3 μm after the process from the primary value of ~ 160 μm. Finite element results exhibit a very significant (~ 85% reduction) decrease in the required load and increase in the strain homogeneity in the HTCEE process compared to its conventional counterpart. This method seems to be very promising for future industrial applications. Keywords Severe plastic deformation . Tube cyclic expansion extrusion . Hydrostatic pressure . AM60 magnesium alloy . Grain refinement
1 Introduction In the last three decades, the production of ultrafine-grained (UFG) and nanostructured (NS) metals and alloys with exceptional physical and mechanical properties has been taken into much consideration. Using severe plastic deformation (SPD) methods where a large plastic strain is implemented, it is possible to produce these materials [1–4]. Equal channel angular pressing (ECAP) [5], accumulative roll bonding (ARB) [6], cyclic extrusion compression (CEC) [7], cyclic expansionextrusion (CEE) [8], high-pressure torsion (HPT) [9], and cyclic extrusion compression angular pressing (CECAP) [10] are several SPD processes for bulk materials. However, few
* G. Faraji [email protected] 1
School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran 111554563, Iran
SPD methods have been developed for producing UFG tubes and hollow specimens [11]. Of them, high-pressure tube twisting (HPTT) [12], the accumulative spin-bonding (ASB) [13], tubular channel angular pressing (TCAP) [14], parallel tubular channel angular pressing (PTCAP) [15], rubber pad tube straining (RPTS) [16], friction stir tube back extrusion (FSTBE) [17], etc. [
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