A retrogression heat treatment was combined with
simultaneous warm forming to produce cross-shaped
stampings from AA7075-T6 Alclad sheet. This process is
termed retrogression forming. A maximum-allowed-
retrogression-forming-time, which includes sheet heat
up, transfer, and stamping, was predicted by calculation
to achieve peak-aged strength through a single reaging
heat treatment after forming. Sheets of 1.6-mm-thick
AA7075-T6 Alclad were stamped at 200 °C to a depth of
45 mm within 2 s without splitting. The formed geometry
exhibits a complexity appropriate to automotive structural
components. These stampings were then subjected to one
of two reaging heat treatments. A full reaging heat
treatment of 120 °C for 24 h produced strength levels in
excess of the original, peak-aged T6 alloy sheet. A sim-
ulated paint bake heat treatment at 185 °C for 25 min
recovered 95% of the strength lost during warm forming.
Successful retrogression forming and reaging of AA7075-
T6 provides new possibilities for stamping high-strength
aluminum alloys into complex geometries without sacri-
ficing strength.
more »
« less
Plastic Flow of AA6013-T6 at Elevated Temperatures and Subsequent Reaging to Regain Full Strength
Combining a retrogression heat treatment with simulta-
neous warm forming can increase the formability of
peak-aged, high-strength aluminum alloys while allowing
peak-aged strength to be recovered through a single
reaging heat treatment after forming. This process is
termed retrogression-forming-and-reaging (RFRA). This
study investigates the applicability of RFRA to AA6013-
T6 sheet material. Elevated-temperature tensile tests were
performed at temperatures from 230 to 250 °C and strain
rates from 3.2 10 −3 to 10 −1 s −1 . Tensile tests were
followed by reaging with a simulated paint-bake heat
treatment. Flow stress at a true strain of 0.10 ranges from
230 MPa (250 °C and 3.2 10 −3 s −1 ) to 290 MPa
(230 °C and 10 −1 s −1 ), significantly lower than the
room-temperature yield strength of 360 MPa in the T6
condition. The average elongation to rupture and reduc-
tion in area from elevated-temperature tests are 22% and
56%, respectively, which are similar to the room-
temperature values for the T4 condition. Elevated-
temperature testing reduced material hardness compared
to the original T6 condition. Subsequent reaging with a
simulated paint-bake raised hardness to 96% of the T6
condition in un-deformed material, but slightly decreased
the hardness of the deformed material. Recommendations
for implementing RFRA of AA6013-T6 are presented.
more »
« less
- Award ID(s):
- 1634495
- NSF-PAR ID:
- 10178662
- Date Published:
- Journal Name:
- Minerals, Metals and Materials Series: Light Metals 2020
- Page Range / eLocation ID:
- 400-405
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Perander, L. (Ed.)Retrogression forming and reaging (RFRA) is a new warm-forming process designed to produce automotive structural components from high-strength aluminum alloys. A scientific approach is described to determine appropriate RFRA conditions for AA7075-T6 and is applied to laboratory-scale forming experiments. The concept of reduced time is used with the activation energy of retrogression measured for AA7075-T6 to predict appropriate times and temperatures for retrogression forming. Conditions recommended for AA7075-T6 are retrogression at 200 °C for 3 to 12 min while forming at strain rates of up to 10^{–1} s^{−1}. The recommended reaging heat treatment to fully restore strength to the T6 condition after retrogression forming is 120 °C for 24 h. These RFRA conditions were successfully applied in laboratory-scale experiments to form AA7075-T6 Alclad sheet and produce a final strength equivalent to the T6 condition. Data from tensile tests provide flow stresses and tensile ductilities across the range of conditions appropriate for RFRA.more » « less
-
Combining retrogression heat treatment with simultaneous warm forming provides an opportunity to significantly increase the formability of high-strength aluminum alloy AA7075-T6 sheet material while subsequently regaining nearly peak-aged strength through a single reaging treatment. This new technological approach to forming high-strength aluminum alloy sheet is termed retrogression forming. Times and temperatures suitable to the retrogression forming of AA7075-T6 sheet material are examined. Differential scanning calorimetry is used to determine the activation energy associated with precipitate dissolution during retrogression. Heat treating experiments determine the changes in hardness during retrogression as a function of temperature and time. The concept of temperature-compensated time is used to construct a master curve that predicts appropriate retrogression forming conditions.more » « less
-
null (Ed.)The deformation behavior of the extruded magnesium alloys Mg2Nd and Mg2Yb was investigated at room temperature. By using in situ energy-dispersive synchrotron X-ray diffraction compression and tensile tests, accompanied by Elasto-Plastic Self-Consistent (EPSC) modeling, the differences in the active deformation systems were analyzed. Both alloying elements change and weaken the extrusion texture and form precipitates during extrusion and subsequent heat treatments relative to common Mg alloys. By varying the extrusion parameters and subsequent heat treatment, the strengths and ductility can be adjusted over a wide range while still maintaining a strength differential effect (SDE) of close to zero. Remarkably, the compressive and tensile yield strengths are similar and there is no mechanical anisotropy when comparing tensile and compressive deformation, which is desirable for industrial applications. Uncommon for Mg alloys, Mg2Nd shows a low tensile twinning activity during compression tests. We show that heat treatments promote the nucleation and growth of precipitates and increase the yield strengths isotopically up to 200 MPa. The anisotropy of the yield strength is reduced to a minimum and elongations to failure of about 0.2 are still achieved. At lower strengths, elongations to failure of up to 0.41 are reached. In the Mg2Yb alloy, adjusting the extrusion parameters enhances the rare-earth texture and reduces the grain size. Excessive deformation twinning is, however, observed, but despite this the SDE is still minimized.more » « less
-
more » « less
Polyurethane and polyurea-based adhesives are widely used in various applications, from automotive to electronics and medical applications. The adhesive performance depends strongly on its composition, and developing the formulation–structure–property relationship is crucial to making better products. Here, we investigate the dependence of the linear viscoelastic properties of polyurea nanocomposites, with an IPDI-based polyurea (PUa) matrix and exfoliated graphene nanoplatelet (xGnP) fillers, on the hard-segment weight fraction (HSWF) and the xGnP loading. We characterize the material using scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA). It is found that changing the HSWF leads to a significant variation in the stiffness of the material, from about 10 MPa for 20% HSWF to about 100 MPa for 30% HSWF and about 250 MPa for the 40% HSWF polymer (as measured by the tensile storage modulus at room temperature). The effect of the xGNP loading was significantly more limited and was generally within experimental error, except for the 20% HSWF material, where the xGNP addition led to about an 80% increase in stiffness. To correctly interpret the DMA results, we developed a new physics-based rheological model for the description of the storage and loss moduli. The model is based on the fractional calculus approach and successfully describes the material rheology in a broad range of temperatures (−70 °C–+70 °C) and frequencies (0.1–100 s−1), using only six physically meaningful fitting parameters for each material. The results provide guidance for the development of nanocomposite PUa-based materials.
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/https://doi.org/10.1007/978-3-030-36408-3_56
