Influence of High-Pressure Torsion Straining Conditions on Microstructure Evolution in Commercial Purity Aluminum

Abstract

The influence of heat generation during severe plastic deformation on microstructure evolution was investigated in commercial purity aluminum (Al 1050, CP-Al) by using high-pressure torsion (HPT) process. The microstructure was characterized by the observations of the torsion and the longitudinal planes. CP-Al disks were deformed by HPT-straining up to 20 turns (equivalent strain, " eq , of $600) at 0.2 or 5 rpm at room temperature. To prevent the increase in specimen temperature, HPT-straining was also carried out in liquid nitrogen. In the all conditions, the value of Vicker's microhardness, Hv, was saturated around 0.65 GPa and the microstructure consisted of the equiaxed grains of about 500 nm with quite low dislocation density. The microstructure in the early stage of HPT-straining showed the deformed (sub)structure, and then the equiaxed grain structure with high-angle boundaries formed by grain subdivision, recovery, continuous recrystallization and grain growth with increase in strain amounts and specimen temperature.

Effect of applied pressure on microstructure development and homogeneity in an aluminium alloy processed by high-pressure torsion

“…For example, the generation of point defects is associated with an increase in volume of the material and the presence of a compressive stress will hinder this process by reducing their formation and mobility rates and hence decreasing the rate of dynamic recovery [29,30].…”

Al–Mg–Cu based alloys and pure Al processed by high pressure torsion: The influence of alloying additions on strengthening

“…5) show markedly different microstructures. Elongated grains are typical results of monotonic HPT straining [33] and ECAP [34] especially with deformation route C. It is well known that both the applied pressure (P) and the number of revolutions (N) influence the development of microhardness in HPT [5,7] and larger numbers of turns and/or higher pressure applied to disks can produce a more homogeneous microstructure.…”

“…Among these techniques, considerable interest has developed in high pressure torsion (HPT) due to the advantage of refining the grain sizes of pure metals and alloys by introducing a continuous and rapid accumulation of high strain without interruption of straining. The microhardness and microstructural evolution occurring during HPT have been investigated extensively, and most attention has been paid to pure and commercially pure metals [4,5,6,7,8,9,10]. Some investigations focused on pure or high purity metals such as pure Cu [4], commercially pure Ti [5] and pure Ni [6,7].…”

“…The microhardness and microstructural evolution occurring during HPT have been investigated extensively, and most attention has been paid to pure and commercially pure metals [4,5,6,7,8,9,10]. Some investigations focused on pure or high purity metals such as pure Cu [4], commercially pure Ti [5] and pure Ni [6,7]. Pure metals are generally too weak for structural applications and therefore they are alloyed with several elements to improve its mechanical properties and inhibit grain growth.…”

Microstructural Evolution in Pure Aluminum in the Early Stages of Processing by High-Pressure Torsion

“…14) No measurements were taken when disks were rotated through fractional numbers of whole revolutions although there are some recent reports of hard-ness measurements taken after less than one whole revolution in Al [18][19][20] and Ti. 21) Accordingly, the present investigation was initiated to extend the earlier work on high-purity Al to cover samples tested through fractional numbers of turns.…”