Effects of short aging on thickening anisotropy of θ′ precipitate and mechanical properties of severe cold-rolled 2519A aluminum alloy plate

Abstract

The commercial 2519 aluminum alloy is a primary material for structural components of aircrafts, helicopters, and amphibians because of its low specific density, which favors the selection of aluminum alloys in weight-critical applications [1, 2]. To promote the mechanical properties of the alloys, severe plastic deformation (SPD) processes were explored such as equal channel angular pressing and severe cold rolling (SCR) [3–8]. However, 2519A aluminum alloy for a new version of Al–Cu alloy was developed as armor material and scarcely fabricated by SPD processes. Valiev has reported that alloys produced by the SPD processes have increased strength with limited ductility [9]. The increase in strength of 5083 aluminum alloy is always accompanied by a loss in ductility [10]. A combination of equal channel angular pressing and lowtemperature aging resulted in significant improvements in both ultimate tensile strength (UTS) and ductility in AA6061 and Al–10%Ag alloy [11, 12]. Short age was scarcely utilized for improving the mechanical properties of the aluminum alloy plate. In this letter, for the first time, short aging treatments are performed to balance UTS and ductility of severe cold-rolled (SCRed) 2519A aluminum alloy. The 2519A alloy plates quenched were rolled from 10 mm to no more than 3 mm in thickness. The total thickness reduction (70–90%) was achieved in multiple passes, with about 10% reduction per pass. The aging temperature of the SCRed aluminum alloy was identified using a differential scanning calorimeter (DSC). Uniaxial tensile tests were conducted at an initial strain rate of 3 9 10 s on SCRed and short-aged (SA) samples along rolling direction. Microstructural observations were carried out using Tecnai G 20 TEM and Sirion 200 SEM. Transmission electron microscopic (TEM) images corresponding to three considered rolling reduction rates are shown in Fig. 1. Cellular structure is observed due to high dislocation density deformed during SCR process regardless of the reduction rate. Dislocation tangle is found in SCRed plates, which were attributed to cross slide (Fig. 1a–c). In fact, there is no obvious difference between three images corresponding although to three different rolling reduction assignments of SCRed plates. However, the fracture surfaces of SCRed plates showed significant differences between each others. The increased sizes of microdimples were found with the increasing rolling reduction rates although in the existence of large dimples (Fig. 2a–c), which could be correlated to the effects of reduction rate on particle sizes. To identify an appropriate aging temperature, DSC experiments were carried out. Figure 3 shows the DSC trace for the SCRed aluminum alloy. From the DSC curve, the onset of aging temperature has been estimated to be 458 and 503 K. For achieving stable microstructures, the SCRed samples underwent short aging treatments for 20 min. TEM images of 2519A alloy short aged at 458 K corresponding to the three different rolling reduction rates are shown in Fig. 4. Only in the sample short aged at 458 K for 20 min corresponding to the rolling reduction rate of 70% (Fig. 4a), thickening anisotropy of h0 precipitate on {100}Al is observed. A similar result is not found in Fig. 4b and c, corresponding to the rolling reduction rate of 80 and X. Zhang (&) Z. Gao Y. Zhao School of Materials Science and Engineering, Central South University, Changsha 410083, People’s Republic of China e-mail: xmzhang_cn@yahoo.cn