Extra Strengthening and Superplasticity of Ultrafine-Grained A2024 Alloy Produced by High-Pressure Sliding

Abstract

In this study, the method of high-pressure sliding (HPS) was applied for grain re nement of an A2024 alloy. Sheet samples with 10-15 mm width and 100 mm length with 1 mm thickness were processed by HPS under pressures of 2-3 GPa. Microstructural observations revealed that the grain size was re ned to 200 nm. Tensile tests showed that the ultimate tensile strength reached 886 MPa with a total elongation of 7.1% and the anisotropy of samples was less developed in the HPS-processed samples. Extra strengthening was attained by aging at 423 K after HPS processing, leading to an ultimate tensile strength of 967 MPa at the peak aged condition. Superplastic elongation of more than 400% appeared when the A2024 alloy processed by HPS for 20 mm was deformed in tension at a testing temperature of 623 K with an initial strain rate of 1.0 × 10 −3 s −1 .

Achieving highly strengthened Al–Cu–Mg alloy by grain refinement and grain boundary segregation

“…An extra peak corresponding to the stable S phase also appeared in the over-aged condition (e.g., in the vicinity of 35 o ). This is consistent with earlier works carried out on a similar material processed by SPD where the S phase was also observed in over-aged conditions [18,22].…”

“…The tensile strength was further increased with increasing N and it reached 910 MPa with the total elongation of 5% after N=10. It should be noted that the higher tensile strength was achieved as compared to an earlier study (890 MPa) [22]. This may be attributed to the larger imposed strain (eq =88 against 13 in [22]).…”

“…Significant strengthening was also reported for UFG A2024 alloys processed by SPD [18,22]. Interestingly, the precipitation sequence usually takes a diffe rent type, with the easy nucleation of stable phase without the classical sequence (through formation of Guinier-Preston-Bagarysatsky (GPB) zones [26]).…”

“…It typically gives rise to a significant increase in the yield stress following the Hall-Petch law [4,5]. This strategy can also be applied to commercial Al alloys [15][16][17][18][19][20][21][22][23][24][25]. Liddicoat et al reported that the tensile strength increased to > 1 GPa in an ultrafine-grained (UFG) A7075 alloy processed by HPT [15].…”

“…shows (a) Vickers microhardness plotted against equivalent strain and (b) stress-strain curves after tensile testing at R.T., where the samples were processed by HPT through N=10 and subsequently aged at 423 K for 35 min. It should be noted that the aging period for 35 min corresponds to peak aging as reported before[22].Fig. 3also includes the strength level for the ST and T6 samples.Fig.…”