Low-Temperature Superplasticity and High Strength in the Al 2024 Alloy with Ultrafine Grains

Abstract

This study aims to achieve an ultrafine-grained (UFG) Al 2024 alloy superplasticity at temperatures lower than the traditional ones for commercial Al alloys (400–500 °C). The UFG structure with a mean grain size of 100 nm produced in the alloy by high-pressure torsion at room temperature provided a very high strength—microhardness (HV0.1) of 286 ± 4, offset yield strength (σ0.2) of 828 ± 9 MPa, and ultimate tensile strength (σUTS) of 871 ± 6 MPa at elongation to failure (δ) of 7 ± 0.2%. Complex tensile tests were performed at temperatures from 190 to 270 °C and strain rates from 10−2 to 5 × 10−5 s−1, and the values of flow stress, total elongation and strain rate-sensitivity coefficient were determined. The UFG alloy was shown to exhibit superplastic behavior at test temperatures of 240 and 270 °C. For the first time, 400% elongation was achieved in the alloy at an unusually low temperature of 270 °C (0.56 Tm) and strain rate of 10−3 s−1. The UFG 2024 alloy after superplastic deformation was found to have higher strength (150–160 HV) than that after the standard strengthening heat treatment T6.

Recent Progress in Creep-Resistant Aluminum Alloys for Diesel Engine Applications: A Review

“…Bobruk et al [68] studied the Al 2024 alloy with ultrafine grains produced by HPT in combination with nanoscale precipitates of Al2CuMg. Tensile mechanical tests at 190, 240, and 270 °C under a strain rate of 10 −3 s −1 demonstrated elongations of 130, 280, and 400%, respectively.…”

“…Al-Cu alloys [33][34][35][36], metal-matrix composites [37][38][39][40][41][42][43][44][45], and additively manufactured aluminum [46][47][48][49][50][51][52] can be used as selective reinforcement materials. Nano-structured aluminum [60][61][62][63][64][65][66][67][68][69] can be used as inserts to improve the creep resistance of the aluminum diesel engine in the inter-valve zone if the thermal stability can be improved. An integrated technology similar to the one that has been proposed for the integration of AM parts into subtractive production processes [82] can be used by employing robot arms to move inserts, molds, and molten alloy to produce the component.…”