Microstructure and Mechanical Properties of Ultra-fine-Grained Al-Mg-Si Tubes Produced by Parallel Tubular Channel Angular Pressing Process

Abstract

In the present work, commercial Al-6061 alloy tubes were processed via multi-pass parallel tubular channel angular pressing (PTCAP). The effects of the number of passes on grain refinement and mechanical properties were investigated. The microstructural evolution was characterized using electron back-scattered diffraction (EBSD) and scanning electron microscopy. The mechanical properties were evaluated using tensile tests and hardness measurements. The EBSD analyses presented that the elongated subgrains or grains with~800 nm in size and a high fraction of low-angle grain boundaries were formed after two PTCAP passes. After four passes, the elongated subgrains have transformed to almost equiaxed grains with~400 nm in size and high-angle grain boundaries. Microhardness of the processed tube increased from 38.9 to 63.4 HV (~63 pct) after three PTCAP passes. An increase in the number of PTCAP passes after three passes has no more effect on the microhardness. Yield and ultimate tensile strength were increased by 2.1 and 1.6 times, respectively, after four PTCAP passes (e~6.4) compared to the annealed sample. Ductile fracture with an extensive necking zone and many big dimples occur in the annealed sample, while fine dimples and limited ductile fracture features were observed in the ultra-fine grained PTCAP-processed samples.

Review of principles and methods of severe plastic deformation for producing ultrafine-grained tubes

“…73 This may be an important advantage of the PTCAP process, making possible processing of tubes longer than possible with the TCAP process. The PTCAP process was applied to pure copper, 102 Al 6061 103 and AZ31 magnesium alloy. 74 Albeit the PTCAP process may produce relatively longer ultrafine-grained tubes compared to TCAP, the problem of thin-wall tube processing remains unsolved.…”

Manufacturing and mechanical characterization of Mg-4Y-2Nd-0.4Zr-0.25La magnesium microtubes by combined severe plastic deformation process for biodegradable vascular stents

“…Achieving a Mg alloy with simultaneous enhanced ductility and strength is one of the important challenges. 44,45 Because of the processing temperature which initiated the recrystallization, grain refinement occurred significantly and grains with the size of 2 and 3 µm appeared in the microstructure of microtubes which is the main cause of having samples with high strength and ductility. This excellent combination of ductility and strength is perfect for stent application where the samples undergo large strains in their actual usage.…”

Mechanical anisotropy in ultra-fine grained aluminium tubes processed by parallel-tubular-channel angular pressing

“…Faraji et al presented the tubular channel angular pressing (TCAP) [24] to produce NS and UFG tubes. They also presented the PTCAP [25] process. In comparison with the TCAP process, the PTCAP process has a number of benefits, such as having higher homogeneity and requiring less process load [26].…”

“…Then, the tube returned into the same shear zones; this time using the second punch is for recovering the primary dimensions of the tube. Although some aspects of properties such as hardness and microstructure [25,27], energy absorption capability [28] and fracture behaviour [29] of UFG tubes have been examined by the PTCAP process, the anisotropic properties of AA 5083 have not yet been investigated.

Figure 1 Schematic of the PTCAP process.

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