Hot working of Ti-6Al-4V via equal channel angular extrusion

Abstract

The deformation behavior of Ti-6Al-4V during high-temperature equal channel angular extrusion (ECAE) with or without an initial increment of upset deformation was determined for billets with either a lamellar or an equiaxed alpha preform microstructure. For conventional ECAE (i.e., deformation by simple shear alone), flow localization and fracture occurred at temperatures between 900 ЊC and 985 ЊC. In contrast, billets deformed at temperatures between 845 ЊC and 985 ЊC using an initial increment of upset deformation immediately followed by the simple shear deformation of ECAE exhibited uniform flow with no significant cracking or fracture. A simple flow-localization criterion was used to explain the influence of preupsetting on the suppression of localization in billets with the lamellar microstructure. The suppression of flow localization for the equiaxed microstructure and the elimination of edge cracking for both types of microstructures were explained in terms of heat transfer (die chill) and workpiece geometry. Further evidence of the relative importance of microstructural and thermal effects was extracted from the results of two-pass extrusions, the first with upsetting and the second without upsetting.

Simulation Of The Material Softening During Hot Metal Forming

“…This can be expressed in different ways. This effect was nicely demonstrated and discussed in the work of DeLo and Semiatin [5]. An example of significant flow localization which finished with intensive shear lines across the material is shown in the Fig.…”

“…To separate the effect of the deformation softening from the influence of other factors (e.g. temperature, strain rate) a number of artificial models of material with different fixed softening rates were constructed and used for numerical simulation of ECAP with the same geometry of extrusion channel as the one used in the work of DeLo et al [5]. b.…”

The Effect of Ram Speed on Mechanical and Thermal Properties in ECAE Process Simulation

“…(3) to this simulation work, calculated strain was $0:91 Â N (where È and É is both 90 ), while resultant average effective strain by this simulation work is $0:7 for 1 pass. However, assumption of homogeneous deformation during ECAE seems not realistic because inhomogeneous deformation may be occurred locally in slip plane for each pass by the die geometry such as the angles of inner and outer arc or friction to the surface of die, 23) which causes inhomogeneous metal flow.…”

“…By Segal, ECAE has proved its unique merits superior to other metal working methods; i.e., uniform structure and properties after working, large equivalent strain per pass without changing its cross-section, relatively low pressure needed for extrusion and controllable shear direction for homogeneous stress-strain state. ECAE process, which loads severe strain into material by simple shear, has been widely attempted by former researchers 1,2) for making ultra fine grained superplastic material and showing its attractive merits, for example, very simple way to give superplasticity into various metals; Al and Al alloys, [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Mg alloys, [18][19][20] Zn-Al and Pb-Sn alloy, 21,22) Ti alloys 23) and steels. [24][25][26] Recently, there have been trials using simulation to analyze ECAE process.…”

Continuous Severe Plastic Deformation Processing of Aluminum Alloys

“…However, there has been only a limited amount of work done in the area of scaling up of SPD processes to produce stock sizes that can be used in commercial forming processes. Work by Semiatin and coworkers [49], Valiev and coworkers [48], Horita, Langdon and coworkers [50], and many others have generally been limited to workpieces in the cross section size range of 10 to 50-mm. Furthermore, much of the published literature on the topic of severe plastic deformation has dealt with the development of SPD processes themselves, or with a scientific study of the properties of the materials that the processes can produce.…”