Presentation
Functional Gradation in Precipitation Hardenable AA7075 Alloy by Differential Cooling Strategies
03/2021
Event name: 19th International Conference on Sheet Metal (SheMet2021)
Description
Inspired by steel forming strategies, this study focuses on the effect of differential cooling
on mechanical properties and precipitation kinetics during hot stamping of high strength AA7075
alloy. For this aim, different forming strategies were performed using segmented and differentially
heated forming tools to provide locally tailored microstructures. Upon processing, uniaxial tensile
tests and hardness measurements were used to characterize the mechanical properties after the aging
treatment. Microstructure investigations were conducted to examine the strengthening mechanisms
using the electron channeling contrast imaging (ECCI) technique in a scanning electron microscope
(SEM). Based on the obtained results, it can be deduced that the tool temperatures play a key role in
influencing the mechanical properties. Lower tool temperatures result in higher material strength and
higher tool temperatures in lower mechanical properties. By changing the cooling rate with the use
of differently heated forming tools, the mechanical properties can be controlled. Microstructure
investigations revealed the formation of very fine and homogeneously distributed particles at cooled
zones, which were associated with elevated mechanical properties, due to the suppression of second
phase particle formation during cooling. In contrast, coarse particles were observed at lower cooling
rates, explaining the lower material strength found in these zones.
