The presented paper provides a modelling strategy for roll forming of a high strength AA7075 aluminum tube. Roll forming allows the cost-effective production of large quantities of long profiles. Forming of high strength aluminum brings challenges like high springback and poor formability due to the low Young’s modulus, low ductility and high yield strength. Forming processes with high strength aluminum, such as the AA7075 alloy, therefore require a detailed process design. Three different forming strategies, one double radius strategy and two W-forming strategies are discussed in the paper. The paper addresses the question whether common roll forming strategies are appropriate for the challenge of roll forming of a high strength aluminum tube. For this purpose, different forming strategies are investigated numerically regarding buckling, longitudinal strain distribution and final geometry. While geometry is quite the same for all strategies, buckling and strain distribution differ with every strategy. The result of the numerical investigation is an open tube that can be welded into a closed tube in a subsequent step. Finally, roll forming experiments are conducted and compared with the numerical results.

The present study provides an overview of previous studies on the welding of the AA7075-T6 aluminum alloy, followed by an investigation of the influence of short-time solution annealing on the mechanical properties of the weld. Conventional laser welding of Al-Zn-alloys leads to a low weld strength, which makes a post weld heat treatment (PWHT) favorable. The PWHT includes solution annealing, quenching and subsequent aging. For solution annealing, different holding times and cooling rates are investigated in this study. The focus of the investigation is on a short solution annealing time, which on the one hand is ecological and economically favorable and on the other hand offers great potential for inline heat treatments. The shortest solution annealing time of 10 s shows a significant increase in weld strength (joint efficiency of 72%), compared to the non-heat treated weld (joint efficiency of 52%). The microstructural analysis reveals that the cooling rate after solution heat treatment affects the formation of precipitates in the microstructure of the welded AA7075 alloy. Moreover, the enhancement of mechanical properties is related to the formation of Mg-Al-Cu and Mg-Zn rich precipitates.

Lightweight design using high‐strength aluminum alloys has gained importance due to the continuing need for weight reduction and increasing crash safety requirements in the automotive industry. There are various manufacturing processes available for processing high‐strength aluminum alloys. Herein, the production of high‐strength aluminum parts by roll forming and stamping based on the example of an AA7075‐T6 hat profile is compared. Roll forming represents a continuous manufacturing process, while stamping is a discontinuous process. Different process routes (T6, W‐Temper and O) for roll forming as well as for stamping (T6, W‐Temper, O and hot forming) are in focus of the investigation. Fundamental differences of the forming processes and the tempering condition are observed and criteria for the choice of the manufacturing process and process route are presented. The temperature‐supported process routes improve the poor cold formability of AA7075 alloy and thus enhance the process window. Potential is offered for both manufacturing processes by applying tailored properties achieved through targeted quenching.

The high-strength AA7075 alloy offers great potential for lightweight construction thanks to its high specific strength. However, high strength and low ductility are challenging for forming the material in the peak-aged T6-condition in terms of material failure and springback. Therefore, this alloy is usually formed in temperature-supported process routes, which poses major challenges for process design. For cold forming of the alloy in the T6-condition, a reliable prediction of material failure is required in terms of process design. Within this study, this is achieved by applying the modified Mohr-Coulomb (MMC) criterion and an increment based damage evolution rule to the FE-model. To validate the failure prediction and verify the general applicability to different profile geometries, two U-profiles and a V-profile are roll formed. Failure occurs during forming for all profile geometries and the experimental results show a good agreement with the failure prediction. The quality of the damage prediction strongly depends on the calibration for the MMC criterion and the setup of the FE-model, depending on the mesh size and the element type used.