The extrusion process of aluminum (Al) and its alloys can be used to produce profiles of various shapes as well as different mechanical properties in order to fulfill the different requirements demanded by different applications. Among these alloys are the Mg- + Si-containing 6XXX heat treatable family of alloys such as 6060, 6061 and 6063. Extruded profiles of these alloys are normally used in the age-hardened condition for architectural uses. The final mechanical properties (such as hardness, elongation, yield strength and ultimate tensile strength) would ultimately depend on the materials structure, i.e. grain size, amount, type and size of hardening precipitates and the grain boundary structure. These variables, however, are normally controlled by the processing route (thermal, mechanical and thermo-mechanical processing steps).
In addition, in extrusion applications, inter-part differences could, indirectly, lead to considerable variations in the processing route, i.e. variations in the thermal and mechanical history of the part, in which case differences or “seemingly” inconsistencies in the resulting properties could occur. Factors affecting the thermo-mechanical history include; extrusion ratio, profile mean thickness, speed of extrusion, position within the billet (i.e., start middle or end part), type of profile (solid or hollow) shape complexity, die and billet temperatures and others.
Ultimately, the establishment of relationship(s) between the different process parameters and the resulting structure(s) is the logical approach to controlling the mechanical properties of the extruded profiles. From a practical point of view, however, this would require a large number of metallurgical examinations covering the many factors mentioned above. In this situation, the design of experiment (DOE) approach could provide an efficient tool for establishing quantitative relationships between any set of inputs (in this case process parameters) and outputs (mechanical properties). After this has been established, a fewer set of metallurgical examinations of some conditions representative of factors of major effects could be carried out with practical time frames and costs.
