Anisotropy in the mechanical properties can cause 'earing' in beverage can bodies. The ears must be cut off, leading to wastage. Photo courtesy of VAW aluminium AG

The properties of aluminium and its alloys, as with most metals, are never completely uniform in all directions - some degree of anisotropy is always present. The exact nature of this anisotropy depends upon both alloy composition and process history (e.g. casting, rolling, extrusion, annealing, etc). Anisotropic properties can have a major effect on subsequent process stages, especially sheet metal forming processes such as deep drawing and stretch forming, and on in-service performance.

Learning Outcomes for this Section

After completing this section, you should be able to:

• provide a definition of the term "anisotropy"
• explain why anisotropy is important, citing examples
• list some key anisotropic material properties (and others which are isotropic)
• recall that anisotropy is a material characteristic dependent on composition and processing history (e.g. mechanical and thermal treatments)
• explain that crystallographic anisotropy is a result of non-random orientation of grains
• relate the terms "texture" and "preferred orientation"
• describe, with the aid of diagrams, how preferred orientation data are presented
• identify some of the most important preferred orientation in aluminium alloys from their "pole figures"

Pre-Requisites

Before starting, it is important that you are familiar with the following terms: % elongation to failure; casting; density; electrical conductivity; extruding; face centred cubic crystal structure of aluminium; heat capacity; Miller index notation for directions and planes in cubic crystals; rolling; tensile stress; thermal conductivity; yield stress; Youngs Modulus;