• Österreicher, Johannes Albert
• Arnoldt, Aurel Ramon
• Höppel, Heinz Werner
• Schiffl, Andreas

Abstract

High-strength Al alloys of the 7xxx series are promising candidates for further light-weighting of car bodies.<br/>However, they are difficult to process by extrusion: complex geometries in particular pose a major challenge due<br/>to high extrusion pressures and tool wear. In addition to process optimization, alloy chemistries can be tailored<br/>for properties such as good extrudability or high strength. In this work, several experimental alloys based on EN<br/>AW 7108A were investigated with respect to the contents of the main alloying elements Zn and Mg, as well as<br/>heat treatment (e.g., homogenization), to achieve good extrudability and favourable mechanical properties. The<br/>experimental alloys were initially extruded on a small-scale extrusion press and evaluated with regards to their<br/>warm formability, microstructure, extrudability, and mechanical properties in T5 temper. Alloy compositions<br/>with Mg contents &lt;1.2 wt.-% are optimal and lead to good extrudability as well as high yield strengths well<br/>above 350 MPa. The Zn content, on the other hand, has minor influence on the extrudability, but significantly<br/>increases strength at higher contents (~60 MPa). However, the combined Zn + Mg content should not exceed 7<br/>wt.-%. Based on these findings, two optimized alloys were designed, direct chill cast on industrial scale, and<br/>extruded on an industrial extrusion press. The alloys showed good extrudability and high strength in the T5<br/>condition. The results also reveal that the limits of the EN AW 7108A alloy are exhausted and higher strengths<br/>could only be achieved with the optimized EN AW 7003 alloy.

Topics

• microstructure
• extrusion
• strength
• yield strength
• homogenization
• alloy composition