A technique for determining aluminum alloy grains crystallographic orientation in polarized light

Аuthors

Voronin S. V.^*, Chaplygin K. K.^**

Samara National Research University named after Academician S.P. Korolev, 34, Moskovskoye shosse, Samara, 443086, Russia

*e-mail: voronin@ssau.ru
**e-mail: chapkostya96@mail.ru

Abstract

The assumption on the possibility of employing interference pattern of aluminum alloys surface in polarized light for determining crystallographic orientation of separate grains was put forward. This assumption was tested on the example of aluminum alloy AD1. Optimum modes of electrolytic etching of AD1 alloy, under which the grains' boundaries were sharply defined, and necessary interference pattern of the grained structure was attained, were defined. Electrolytic etching was being performed in a 40% solution of hydrofluoric acid, boric acid and distilled water at 1.7-1.9 A, 100-110 V, and etching time duration of two minutes. It was established that the interference pattern of the sample surface changes with prolonged exposure in the open air. This was due to the oxide film's growth process. Employing literature data on elasticity modulus of aluminum mono crystals depending on crystallographic direction, the article defines the relationship between the grain elasticity modulus and its crystallographic orientation over three directions by the scanning probe microscopy method using NanoScan-3D device. Scanning of the studied section with a size of 128 х 128 µ m was carried out at a speed of 30 µ m/sec.During the scanning process, the signal from the indentation sensor was recorded and processed, resulting in a surface profile map (Z_opt). Modulus of elasticity of separate grains was determined by the method of removing the curves of the indenter's supply to the surface of the sample for each grain in the section under study.

While comparing the interference pattern with the distribution of modulus values, it was found that the grains of blue color corresponded to minimum values of modulus of elasticity from 46 to 55 GPa. Maximum values of modulus of elasticity were in the range from 69 to 78 GPa, and corresponded to yellow grains. It was established also that pale orange grains correspond to modulus of elasticity from 55 to 64 GPa. As a result, the assumption was made that the blue grains have a crystallographic direction [100], since they have minimum modulus of elasticity in the array of obtained values. Yellow grains have a crystallographic orientation [111] and maximum modulus of elasticity from the values obtained. Pale orange grains occupied an intermediate position by value of modulus of elasticity, so it was assumed that their crystallographic direction corresponds to [110].

The developed technique is characterized by simplicity, low energy intensity, and less time consuming, in contrast to the methods traditionally used for this purpose. This technique can also be employed to determine the crystallographic orientation of individual grains of other aluminum alloys.

Keywords:

aluminum, crystallographic orientation, polarized light, electrolytic etching

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