Evaluation of the Engineering Properties of a Commercially Produced Aluminum Alloy 2020-T651 Plate

摘要

Al-Cu-Li alloy 2020 was developed in the 1950's to help satisfy the need for high strength and high modulus of elasticity in an aircraft structural material. The fracture toughness of alloy 2020 is comparatively low compared to other aerospace alloys. This characteristic coupled with manufacturing difficulty eventually led to the withdrawal of alloy 2020 for use in commercial products. Despite this setback, Aluminum alloys containing lithium remain attractive for aircraft applications because in addition to high strength and high elastic modulus, they possess low density and the potential for higher resistance to fatigue. Consequently, current research has been directed toward increasing fracture toughness of Al-Li type alloys into a range acceptable for aircraft use. This report summarizes tensile, fracture toughness and fatigue crack growth properties obtained from a commercially produced lot of aluminum alloy 2020-T651 plate. This characterization is intended to serve as a baseline for alloy development work directed at improving damage tolerant characteristics of Al-Li type alloys. The fracture toughness characterization includes plane-strain fracture toughness (KIc) values, crack growth resistance (R) curves, as well as results from fracture toughness indicator tests; namely, the Kahn-type tear test and the slow bend precrack charpy test. Obtained fatigue crack growth rates traverse the entire range from near-threshold values to the exceedingly high rates encountered as delta K values approach the material toughness. Metallographic characterization of alloy 2020-T651 in addition to fractographic results from a fatigue crack growth test specimen are also included in this report.