Mechanical Properties and Microstructural Evolution in Al 2014 Alloy Processed Through Multidirectional Cryoforging

Mechanical properties and microstructure evolution of Al 2014 alloy subjected to cryoforging (MDF) to a cumulative strain of 1.2, 1.8, and 2.4 were investigated in the present work. The deformed samples after 4 cycles at a cumulative strain of 2.4 shows the formation of ultrafine grain sizes in the range of 100-450 nm with high-angle grain boundaries as observed from TEM analysis. The tensile and hardness of the deformed sample were measured by Universal Testing machine and Vickers hardness Tester, respectively. The tests were also conducted for sample deformed at room temperature to compare with cryo-forged samples. The sample deformed at cryogenic temperature up to a cumulative strain 2.4 shows an improvement of tensile strength, hardness, and apparent fracture toughness (K-Q) from 318 MPa to 470 MPa, 103HV to 171 HV, and 23.93 MPa to 37.7 MPa respectively, with decrease in ductility from 18% to 6% as compared with solution-treated alloy. The cryo-forged Al 2014 alloy exhibits an increment of 7% in tensile strength, 3% in yield strength, and 3% in hardness up to cumulative true strain of 2.4 as compared to the samples forged at room temperature. The improvement in tensile properties of MDFed alloy is attributed to dislocation strengthening and grain boundary strengthening effect at both temperatures. The effective suppression of cross slip and climb at liquid nitrogen temperature improves the strength of cryo-forged sample better than that of room temperature-forged alloy.