Verfestigung vorkonditionierter Aluminiumbleche/Solidification of preconditioned aluminium sheets – Influence of the heat treatment condition within a multi-stage forming process

Abstract

Mittels einer Vorkonditionierung in den W-Temper- (W-) oder weichgeglühten (O-) Zustand kann die Umformbarkeit der hochfesten Aluminiumlegierungen EN AW-6082 und -7075 signifikant gesteigert werden. Die so realisierbare Kaltumformung sorgt vor allem bei mehrstufigen Anwendungen für eine vereinfachte Prozessführung gegenüber temperaturunterstützten Prozessrouten, führt jedoch zu ausgeprägten Verfestigungseffekten. Deren Klassifizierung und Quantifizierung sind Inhalt dieses Beitrags.   By means of preconditioning to the W-temper- (W-) or soft-annealed (O-) state, the formability of the high-strength aluminium alloys EN AW-6082 and -7075 can be increased significantly. These preconditioned alloys enable cold forming, which ensures simplified process control compared to temperature-supported process routes, especially in multi-stage applications. In return, this leads to pronounced strain-hardening effects. Their classification and quantification are the subject of this article.

Opportunities, Challenges, and Influencing Factors in the Forming of Preconditioned Semi‐Finished Products Made of EN AW‐6082 and ‐7075

“…[28] Additionally, the 7ÂÂÂ alloy is more sensitive to natural aging than the 6ÂÂÂ alloy. [8] For a more precise characterization of individual influencing parameters, the following process parameters of preconditioning and forming are varied within the tensile tests: 1) The drawing speed v draw is reduced from the standard 0.2 mm s À1 by a factor of 10-0.02 mm s À1 or increased to 2.0 mm s À1 for all three conditions. 2) The rolling direction of the material is examined at 0°as well as 45°and 90°for all conditions to investigate potential anisotropic material behavior.…”

“…While a specimen of EN AW-6082 is formable in the cup draw example, the part made of EN AW-7075 breaks into several pieces. [8] Even if forming is possible, the springback behavior of the higher strength alloy poses a further challenge, as shown by the 90°d ie bending with a 20 mm radius in Figure 1b. [9] To extend formability [10,11] and reduce springback, [11,12] higher temperatures and thus temperature-supported process routes are applied.…”

“…[10] This is contrasted on the one side by the need for subsequent heat treatment to achieve the high-strength T6 material properties [14] and on the other side by pronounced strain hardening. [8] In multistage forming, as required to produce complex components, the above process routes are challenging because of the heat transfer [18] that occurs in warm and hot forming and strain hardening [8] in cold forming.…”

“…While a specimen of EN AW‐6082 is formable in the cup draw example, the part made of EN AW‐7075 breaks into several pieces. [ 8 ] Even if forming is possible, the springback behavior of the higher strength alloy poses a further challenge, as shown by the 90° die bending with a 20 mm radius in Figure 1b. [ 9 ]…”

“…[ 10 ] This is contrasted on the one side by the need for subsequent heat treatment to achieve the high‐strength T6 material properties [ 14 ] and on the other side by pronounced strain hardening. [ 8 ]…”