Functional Gradation in Precipitation Hardenable AA7075 Alloy by Differential Cooling Strategies

Abstract

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.

Hot Sheet Metal Forming Strategies for High‐Strength Aluminum Alloys: A Review—Fundamentals and Applications

“…In addition, the effect of differential cooling, as proposed for high-strength steel, [198,199] on precipitation-hardenable aluminum alloys using this novel forming process should be considered. [200,201]…”

Microstructural Influences Caused by Different Aging Strategies on the Strain-Dependent Damping of the High-Strength Aluminum Alloy AA7075

“…In contrast, the overaged T7-2 condition had a lower damping than the T7-1 condition. This may be due to a possible increase in grain size or differences in the amount and type of precipitates resulting from the differing aging temperatures and times [12][13][14].…”

Plasmonic nanotechnology for photothermal applications – an evaluation

“…Often, nanomaterials are used in conjunction with a phase-change material for energy storage applications, and when plasmonic nanoparticles are integrated into a solid phasechange material (n-PCM), the energy balance equation is be given by [94]: (36) ΔH fus is the heat of fusion, ρ s is the density of solid, ϕ is the volume fraction of the particles, T m is the melting temperature, T c is the temperature of the cooling fluid, W is the thickness of the compartment holding the n-PCM, k w is the conductivity of the wall, and k′ is the conductivity of the PCM. The thermal conductivity of the plasmonically enhanced PCM materials can be varied with the volumetric fraction of the PCM material and can be specified by [95]: (37) k B is the Boltzmann constant, β k = 8.4407 × (100ϕ) −1.07304 , f(T,ϕ) = (2.8217 × 10 −2 ϕ + 3.917 × 10 −3 ) T/T ref + (−0.669 × 10 −2 ϕ − 3.91123 × 10 −2 ), K np and K PCM are the thermal conductivities of nanoparticles and PCM, respectively, ϕ is the volumetric fraction of the nanoparticles, ρ np and ρ PCM are the densities of nanoparticle and PCM, respectively, and C pPCM is the specific heat capacity of the PCM.…”