Abstract
A major challenge in processing 7xxx series aluminum alloys is their limited formability at room temperature. In this paper, for the alloys EN AW-7020 and EN AW-7075, various variants of the W-temper forming process are investigated. For both alloys, a good cold formability and a high strength after aging can be achieved. The effects of solution heat treatment or retrogression temperature and holding time, as well as the influence of plastic deformation after quenching, were studied. For various combinations of process parameters, the formability of the as-quenched materials and the hardening performance during artificial aging were examined. For this, hardness measurements and differential scanning calorimetry (DSC) experiments were performed along the entire process chain, to reveal the development of the hardening precipitates. After solution heat treatment and quenching, the yield stress and hardness of both investigated alloys were drastically reduced in comparison to their initial T6 states, while the ductility was significantly increased. By a subsequent simple artificial aging treatment, the same hardness as in the T6 state could be restored. It was observed that plastic deformation immediately after quenching significantly decreased the artificial aging time to achieve the peak hardness. Besides the conventional solution heat treatment process, an alternative retrogression and re-aging procedure was identified for the alloy EN AW-7020. While the heat treatment temperature can be reduced as compared to the conventional solution heat treatment, the formability and hardenability are equally good. In contrast, no such alternative process could be identified for the alloy EN AW-7075.
Highlights
Due to the high strength-to-weight ratio of 7xxx series aluminum alloys, they gain increasing attention for producing high performance sheet metal components
Besides the conventional solution heat treatment process, an alternative retrogression and re-aging procedure was identified for the alloy EN AW-7020
While the heat treatment temperature can be reduced as compared to the conventional solution heat treatment, the formability and hardenability are good
Summary
Due to the high strength-to-weight ratio of 7xxx series aluminum alloys, they gain increasing attention for producing high performance sheet metal components. These heat treatable alloys owe their strength to the formation of precipitates during heat treatment processes [1]. The main alloying elements of this series are zinc and magnesium, and sometimes copper, providing the highest strengthening potential among all age-hardenable aluminum alloys Alloys of this series have great potential for application as high strength sheet materials in the aerospace and automotive industry [2]. In order to achieve the desired strength of the final product, in industrial applications, the material is heated above the temperature at which the strengthening precipitates dissolve and subsequently quenched to a supersaturated solid solution.
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