Abstract
The evolution of mechanical properties of a third-generation Al–Cu–Li alloy, AA2050, with different initial tempers (as-quenched WQ, naturally aged T34 and peak-aged T84) during creep-ageing has been investigated in this study. A set of creep-ageing tests was carried out under 150 MPa at 155 °C with different durations for all initial temper conditions and tensile tests were performed subsequently to acquire the main mechanical properties of the creep-aged alloys, including the yield strength, ultimate tensile strength and uniform elongation. The evolution of these mechanical properties during creep-ageing has been discussed in association with precipitation behaviour of AA2050 alloys with different initial tempers. The results indicate that the T34 alloy is the best choice for creep age forming (CAF) applications among these initial tempers, as it provides better yield strength and uniform elongation concurrently after creep-ageing. In addition, a work hardening rate analysis has been carried out for all the creep-aged alloys, helping to understand the detailed dislocation/precipitate interaction mechanisms during plastic deformation in the creep-aged AA2050 alloys with WQ, T34 and T84 initial tempers.
Highlights
Creep age forming (CAF) is an advanced forming technology originally proposed to manufacture large/ extra-large panels in the aerospace industry [1]
A substantial work hardening behaviour is observed in the alloy during plastic deformation, which can be explained by the high efficiency of dislocation storage during plastic deformation due to the high level of free solutes in the supersaturated solid solution (SSSS) of the alloy [17]
Significant serrations, known as the Portevin–Le Chatelier effect, are observed in the stress– strain curve of the initial WQ alloy, which is related to the SSSS state of the alloy, as sufficient free solutes in the alloy matrix can diffuse around dislocations to restrain its movement, leading to serrations during plastic deformation [17,24]
Summary
Creep age forming (CAF) is an advanced forming technology originally proposed to manufacture large/ extra-large panels in the aerospace industry [1]. Different precipitation behaviour has been found during artificial ageing of aluminium alloys, such as Al–Mg–Si [9] and Al–Li [10,11] alloys, with as-quenched or naturally aged initial tempers. Only the yield strength of the alloys after creep-ageing was considered in previous studies, other mechanical properties, such as ultimate tensile strength (UTS) and uniform elongation, are important for the CAFed alloys and should be considered as well, so as to provide a comprehensive method to select the proper initial temper condition for alloys for CAF applications. An Al–Cu–Li alloy, AA2050, with three commonly reported initial temper conditions, as-quenched, naturally aged and peak-aged, was studied to investigate the effect of initial temper on evolutions of mechanical properties, including yield strength, UTS and uniform elongation, during creep-ageing in CAF process. The plastic deformation behaviour of the creep-aged alloys is discussed based on the work hardening rate analysis, so as to understand the detailed dislocation/precipitate interaction mechanisms in creep-aged AA2050 alloys
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