An Experimental Investigation of Hot Forming Effects on Mechanical Properties of High-Strength Aluminum Alloys AA6082 and AA7075

Aluminum alloys are widely used as light-weight manufacturing materials in the automotive and aerospace industry because of their excellent strength-to-weight ratio. Hence, for these applications, the chosen alloys require to perform in a multitude of forming processes. However, parts such as hoods and trunk lids undergo complex stress-strain-paths in traditional process strategies, where several phenomena interfere with the accurate forming of high-strength aluminum sheets. To overcome this challenge, a novel hot forming process offers an approach for increasing formability and reducing springback in the resulting geometry without losses in mechanical strength. This new thermo-mechanical route combines simultaneously hot forming and quenching of a blank in forming tools within the course of a solution heat treatment. In this study the influence of temperature (different temperature levels in comparison to conventional solution heat treatments), soaking and artificial aging time on mechanical properties of two different aluminum alloys AA6082-T4 and AA7075-T6 is systematically studied using this new hot forming method. To evaluate the effects of the new manufacturing technology on the particular material, Vickers hardness measurements and uniaxial tensile tests are carried out to characterize mechanical properties as well as the strengthening and formability behavior of the sheet materials. The resulting properties are, therefore, compared to those coming from the conventional forming process of the investigated material in as-received condition (AA6082-T4 and AA7075-T6). With the new process an increase of geometrical accuracy can be confirmed, due to reduced springback. The experimental results of the mechanical tests reveal for both alloys (AA6082 and AA7075) no obvious increase in yield and ultimate tensile strength with increasing heat treatment temperature (from 480 degrees C to 540 degrees C) and soaking time (from 0 s to 1800 s), but a slight increase with increasing aging time. Moreover, depending on the aluminum alloy, a minor increase in mechanical behavior after being formed was found, using this new manufacturing technique compared to the initial condition. These effects observed are related to the strengthening mechanisms during the thermo-mechanical process, contribution of aging and the underlying initial microstructure.