Evolution of Microstructure and Hardness in Pure Al by Twist Extrusion

Abstract

High purity Al (99.99%) is subjected to severe plastic deformation (SPD) at room temperature using a process of twist extrusion (TE). The microstructure evolution and the related change in microhardness are examined with respect to imposed strain. It is shown that subgrains develop after the first TE pass with a size of $1:6 mm and this size remains essentially the same for further application of TE passes. However, dislocations become less visible within grains and grain boundaries become straight and well-defined with misorientation angle higher as the imposed strain is increased. The hardness increases with imposed strain when the magnitude of the strain is small. However, as the imposed strain is large, the hardness decreases due to a reduction of dislocations within grains. It is confirmed that these results obtained with TE are consistent with those reported using equal-channel angular pressing (ECAP) and high pressure torsion (HPT), indicating that the microstructural change and the variation of related mechanical properties with straining observed in pure Al are not affected significantly by the methods of SPD processing.

Microhardness Distribution and Microstructural Evolution in Pure Aluminum Subjected to Severe Plastic Deformation: Elliptical Cross-Sectioned Spiral Equal-Channel Extrusion (ECSEE)

“…These techniques include equalchannel angular pressing (ECAP) (Ref [5][6][7][8], high-pressure torsion (HPT) ( Ref 3,9,10), torsion-extrusion (TE) (Ref [11][12][13][14], combined tension-torsion (CTT) ( Ref 15,16) and elliptical cross-sectioned spiral equal-channel extrusion (ECSEE) (Ref [17][18][19][20][21]. All of these procedures are capable of introducing large plastic straining and significant microstructural refinement in bulk crystalline solids.…”

Microstructure Evolution in Pure Al Processed with Twist Extrusion

“…21) In our earlier study, 25) TEM observations and microhardness data of this investigation have been reported. The present report is mostly concentrated on analysis of structure evolution through optical microscopy and Electron Back-…”

“…These observations are in a reasonable agreement with earlier results on microhardness and dislocation structure evolution reported in. 25) 4. Summary and Conclusions…”

“…12,15,25) For the tool parameters used in this study, average true strain of " ave % 1:2 was introduced for a single pass. 12) This level of strain is comparable to strain introduced in a billet after 1 ECAP pass through 90 channel intersection die or 70% reduction in rolling.…”

Microstructure and Mechanical Properties of Copper Processed by Twist Extrusion with a Reduced Twist-Line Slope

“…Twist extrusion (TE) was introduced [5] as an attempt to scale-up the process of high-pressure torsion. Being promising in the commercial sense, [6] TE enjoyed some interest, which is reflected in continuous research on the subject [7][8][9][10][11][12][13] as well as in the emergence of new SPD methods inspired by the concept of TE. [14][15][16][17][18] In the quest to incorporate TE into the industry, such issues as endurance of the tool are becoming important.…”