Formability of Aluminum Alloy Sheet At Elevated Temperature

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Abstract

An experimental and numerical study of the isothermal and non-isothermal warm formability of an AA3003 aluminum alloy brazing sheet is presented. Forming limit diagrams were determined using warm limiting dome height (LDH) experiments with in situ strain measurement based on digital image correlation (DIC) techniques. Forming limit curves (FLCs) were developed at several temperature levels (room temperature, 100°C, 200°C, 250°C, and 300°C) and strain-rates (0.003, 0.018, and 0.1s⁻¹). The formability experiments demonstrated that temperature has a significant effect on formability, whereas forming speed has a mild effect within the studied range. Elevating the temperature to 250°C improved the formability more than 200% compared to room temperature forming, while forming at lower speeds increased the limiting strains by 10% and 17% at room temperature and 250°C, respectively.

Non-isothermal deep draw experiments were developed considering an automotive heat exchanger plate. A parametric study of the effects of die temperature, punch speed, and blank holder force on the formability of the part was conducted. The introduction of non-isothermal conditions in which the punch is cooled and the flange region is heated to 250°C resulted in a 61% increase in draw depth relative to room temperature forming.

In order to develop effective numerical models of warm forming processes, a constitutive model is proposed for aluminum alloy sheet to account for temperature and strain rate dependency, as well as plastic anisotropy. The model combines the Barlat YLD2000 yield criterion (Barlat et al., 2003) to capture sheet anisotropy and the Bergstrom (1982) hardening rule to account for temperature and strain rate dependency. Stress-strain curves for AA3003 aluminum alloy brazing sheet tested at elevated temperatures and a range of strain rates were used to fit the Bergstrom parameters, while measured R-values were used to fit the yield function parameters. The combined constitutive model was implemented within a user defined material subroutine that was linked to the LS-DYNA finite element code. Finite element models were developed based on the proposed material model and the results were compared with experimental data. Isothermal uniaxial tensile tests were simulated and predicted responses were compared with measured data. The tensile test simulations accurately predicted material behaviour.

The user material subroutine and forming limit criteria were then applied to simulate the isothermal warm LDH tests, as well as isothermal and non-isothermal warm deep drawing experiments. Two deep draw geometries were considered, the heat exchanger plate experiments developed as part of this research and the 100 mm cylindrical cup draw experiments performed by McKinley et al. (2010). The strain distributions, punch forces and failure location predicted for all three forming operations were in good agreement with the experimental results. Using the warm forming limit curves, the models were able to accurately predict the punch depths to failure as well as the location of failure initiation for both the isothermal and non-isothermal deep draw operations. the

Cited Works (5)

Year	Entry
2010	Mckinley J. Warm Forming of Aluminum Brazing Sheet: Experiments and Numerical Simulations [Master's thesis]. University of Waterloo; 2010.
1948	Hill R. A theory of the yielding and plastic flow of anisotropic metals. Proc R Soc Lon Ser-A. May 27, 1948;193(1033):281-297.
2006	van den Boogaard AH, Huétink J. Simulation of aluminium sheet forming at elevated temperatures. Comput Meth Appl Mech Eng. October 1, 2006;195(48-49):6691-6709.
2003	Barlat F, Brem JC, Yoon JW, Chung K, Dick RE, Lege DJ, Pourboghrat F, Choi S-H, Chu E. Plane stress yield function for aluminum alloy sheets, I: theory. Int J Plast. September 2003;19(9):1297-1319.
1982	Bergström Y, Hallén H. An improved dislocation model for the stress-strain behaviour of polycrystalline α-Fe. Mater Sci Eng. August 1982;55(1):49-61.

Cited By (5)

Year	Entry
2014	Boba M. Warm Forming Behaviour of ZEK100 and AZ31B Magnesium Alloy Sheet [Master's thesis]. University of Waterloo; 2014.
2016	Jain E. Investigation of Effect of Temperature and Forming Speed on the Formability of AA3003 Brazing Sheets [Master's thesis]. University of Waterloo; 2016.
2016	Verma R. Effect of Elevated Temperature on Mechanical Behaviour and Springback of Aluminum Alloy Brazing Sheets [Master's thesis]. University of Waterloo; 2016.
2018	Cyr ED. A New Crystal Plasticity Formulation to Simulate Large-Strain Plasticity of Polycrystalline Metals At Elevated Temperatures [PhD thesis]. University of Waterloo; 2018.
2017	Noder J. Characterization and Simulation of Warm Forming of 6xxx and 7xxx Series Aluminum Alloys [Master's thesis]. University of Waterloo; 2017.