Abstract
At first the direction of crystallization of zinc was investigated by the interference-dilatometric method, and the following results were obtained, the length of the specimen being about 13 mms.
When the velocity of cooling is small, crystals become columnar and hexagonal, the base being nearly parallel to their axes. The curve I, Ia, IIa of Fig. 3, 4, and 5 show the distributions of expansion coefficients of a cast specimen. When the specimen is rolled the distribution changes as shown in the figures. The directions of hexagonal axes of a rapid cooled specimen, initially distributed evenly in the chill surface, becomes nearly parallel to the direction of rolling, the plane of rolling coinciding with the chill surface.
Then mechanical twins are formed and most of the hexagonal base become nearly parallel to three coordinate planes of the specimen, if the axes are taken as the direction of rolling, perpendicular to the plane of rolling and perpendicular to each of them. If the direction of rolling coincides to that of crystal growth, the deformation of the rapidly cooled ingot becomes extremely easy, cracks do not occur, accompanying mechnical twins and the larger part of the hexagonal bases become perpendicular to the direction of rolling.
