Formability and failure mechanisms of AA2024 under hot forming conditions

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 528; no. 6; pp. 2648 - 2656
• Main Authors: Wang, L., Strangwood, M., Balint, D., Lin, J., Dean, T.A.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 15.03.2011; Elsevier
• Subjects: AA2024; Aluminum base alloys; Applied sciences; Ductility; Exact sciences and technology; Formability; Forming; Fracture mechanisms; Fractures; High temperature; Hot forming; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Production techniques; Scanning electron microscopy; Softening; Stamping; Structural materials; Fracture mechanisms; Hot forming; Formability; AA2024; Scanning electron microscopy; Aluminium base alloys; Ductility; Rupture; Tension test; Grain boundary; Fatigue strength; Fractography; Fracture mode
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2010.11.084

▶ Forming AA2024 sheet at its solution heat treatment (SHT) temperature is studied. ▶ Formability is shown to be extremely low for AA2024 at the SHT temperature. ▶ The cause of low SHT temperature formability of AA2024 is found by experiment. ▶ An attainable high formability window (temperature and speed) is found for AA2024. ▶ AA2024 formability may be dramatically increased by elevated temperature stamping. Aluminium alloy 2024 (AA2024) is extensively used as a structural material in the aircraft industry because of its good combination of strength and fatigue resistance. However, complex shaped components, particularly those made from sheet, are extremely difficult to form by traditional cold forming due to its low ductility at room temperature. A possible solution of this problem is to form sheet workpieces at elevated temperature. The aim of the work described in this paper is to determine the relationship between formability and temperature for AA2024 by conducting a series of tensile tests at elevated temperatures ranging from 350 to 493°C. Ductility of AA2024 was found to increase gradually with increasing temperature up to 450°C, followed by a sharp decrease with further increase in temperature. So-called cup tests confirmed that the formability of AA2024 is very high at a temperature of about 450°C. Fracture surfaces and longitudinal sections of formed samples were examined by scanning electron microscope. It was found that fracture occurred in three different modes depending upon the temperature, and the sharp decrease in ductility when the temperature exceeds 450°C was caused by softening of grain boundaries by solute enrichment (at higher heating rates liquation may be involved) and softening of the matrix around inclusion particles.