Crystallographic Anisotropy of Columnar Zone in Aluminum Weld Metal :

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Abstract

By X-ray diffraction technique the preferred orientation in columnar zone in TIG-arc weld metal has been investigated for commercially pure aluminum (1S and 2S) 1 mm thick sheets. Main conclusions obtained are as follows : (1) The preferred orientation in the columnar zone in the weld metal is [100] fiber texture as said in castings. (2) The fiber texture is usually formed near the fusion boundary. (3) The direction of the fiber axis follows that of the maximum temperature gradient as far as the latter gradually changes as inward growth proceeds. The change in the direction of the fiber axis is accomplished by the competitive growth of the columnar crystals and the columnar growth of the stray crystals which are newly originated inside the weld metal. (4) In an elliptical shaped puddle the angle between the direction of the fiber axis and the welding direction changes from nearly 90° at the fusion boundary to 0° at the weld center as inward growth proceeds. However in a tear-drop shaped puddle the angle is maintained at a constant value from the fusion boundary to the weld center, which is increased to 90° with an increase in welding speed. (5) From metallographic observations on the origination of the stray crystal it is recognized that the growing direction of the subgrains in a stray crystal agrees with the normal to the weld ripple at its origin, while that in the original columnar crystal for which the stray crystal has been substituted considerably deviates.

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