Abstract
The evolution of mechanical properties of a third generation Al-Cu-Li alloy, AA2050, with different initial tempers (T34 and as-quenched (WQ)) during creep-ageing has been investigated and analysed in this study. A set of creep-ageing tests under 150 MPa at 155 °C for up to 24 h was carried out for both 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 (UTS) and uniform elongation. Precipitation behaviour of the T34 and WQ AA2050 alloys has been summarised and successfully explains the detailed evolutions of the obtained mechanical properties of the alloy with these two initial tempers during creep-ageing. The results indicate that the T34 alloy can be a better choice for creep age forming (CAF) process compared with WQ alloy, as it provides better yield strength and uniform elongation properties concurrently after creep-ageing. In addition, a work hardening rate analysis has been carried out for all the creep-aged alloys, helping to reveal the detailed dislocation/precipitates interaction mechanisms during plastic deformation in the creep-aged T34 and WQ AA2050 alloys.
Highlights
Creep age forming (CAF) is an advanced forming technology originally proposed to manufacture large/extra-large panels in the aerospace industry, in which the plastic deformation and age hardening occur simultaneously in the material during the process [1]
According to the stress-strain curves shown in Fig. 3(a), the as-received T34 alloy shows a relatively high yield strength of about 269 MPa with a significant work hardening behaviour
Apparent serrations, known as the Portevin-Le Chatelier effect, can be observed in the stress-strain curve of the as-received T34 alloy. This phenomenon may indicate that only minor stable clusters exist in the as-received alloy and sufficient solutes in the alloy matrix can diffuse around dislocations to restrain its movement, leading to the observed serrations during plastic deformation [9, 10]
Summary
Creep age forming (CAF) is an advanced forming technology originally proposed to manufacture large/extra-large panels in the aerospace industry, in which the plastic deformation and age hardening occur simultaneously in the material during the process [1]. While for CAF process, the creep-ageing behaviour of an Al-Cu-Li alloy (AA2050) with different initial tempers, namely the as-quenched (WQ), T34 and T84, has been investigated and compared, showing different creep strain and age hardening properties under the same stress level at 155 oC [2]. 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 way to select alloys with a proper initial temper condition for CAF applications. The plastic deformation behaviour of the creep-aged alloys is discussed based on a work hardening rate analysis, so as to reveal the detailed dislocation/precipitates interaction mechanisms related to the mechanical properties of the creep-aged AA2050
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