Press Form Hardening of Aluminium Alloys 7021 and 6082. A Feasibility Study.

Abstract

Aluminium alloys 6082.25 and 7021.50 were evaluated and compared as potential base materials for processing by press form hardening. Both extruded profiles and rolled sheets were assessed, however the rolled 7021 material was neglected early in the project due to time constraints. The effect of deformation at the relevant high temperatures and strain rates on the workability and microstructure of the materials was assessed. The artificial age hardening response subsequent to hot deformation was investigated for the 6082 rolled material.

The flow stress and workability of all investigated materials was highly favorable for forming at all temperatures relevant to press form hardening. These properties were most favorable at the solution heat treatment temperatures of the respective alloys. Materials that do not recrystallize during solution heat treatment appeared to give an advantageous grain structure in the finished parts. The extruded materials in this work did not recrystallize in bulk during solution heat treatment nor hot deformation, however recrystallization in the surface layers was not assessed. No disfavor of the fibrous grain structure associated with extruded materials was observed regarding workability at the relevant temperatures, thus extruded materials could be particularly suitable as base materials for press form hardening.

The AA7021.50 extruded material appeared especially suitable for press form hardening due to a particularly high workability and low flow stress at the relevant forming conditions. The superior resistance to recrystallization in this material further favored it as a suitable base material for press form hardening.

No detrimental effect of the hot deformation on the artificial ageing response was observed in the AA6082.25 rolled material. This should however be further and more thoroughly assessed for all potential base materials.