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Division of Materials Science and Engineering, Graduate School of Engineering, Hokkaido University Japanese

Introduction to Metallurgy

What is dendrite?

Dendrite is one of the most commonly observed structures of crystal druing solidification of metallic materials. It is tree-like shape having a trunk and branches.

When an alumina tube was dipped into a supercooled liquid aluminum, a dendritic crystal of aluminum grew from the surface of the alumina tube as shown in the figure on the right.

Solidification structure of a liquid film remained on a crucible wall exhibits a dendritic relief pattern shown on the right side.

The figure on the right shows dendrites that have grown from the outer surface of a water-cooled cupper pipe dipped into an Al-Cu alloy liquid. When the cupper pipe was pulled up from the alloy liquid and then it was rapidly rotated to remove the liquid remaining between dendrites using the centrifugal power, the dendritic structure appeared on the surface of the solidified alloy.

Observation of microstructures

Let' s have a look at a macrostructure of an aluminum ingot cast into a cylindrical shape. The ingot was longitudinally sectioned, mounted in a resin, and polished using emery papers, but no structures can be seen at this stage.

After dipping the sample in an aqua regia (mixture of hydrochloric and nitric acids) for about 20 seconds, a pattern showing a columnar grain structure appeared.

This corrosive action by an acid to reveal metal structure is called etching. A large structure that can be seen with naked eye is called a macrostructure, while a small structure that can be seen using a microscope is called a microstructure.

Laboratory of Microstructure Control

Kita 13 Nishi 8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan Access
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