Influence of Stress Amplitude and Loading Frequency on Fatigue Performance of AA2024 Alloy under Two Temper Conditions

Abstract

AA2024 aluminium alloy is commonly used in fatigue-sensitive aerospace structures, but the relative effects of temper condition, stress amplitude and loading frequency on its fatigue durability are not sufficiently quantified. The present work examines the fatigue performance of AA2024-T3 and AA2024-T6 using Taguchi L9 experimental design with maximum stress level and loading frequency as chosen factors at two levels. Fatigue tests were performed at a sinusoidal tension-to-zero loading followed by Taguchi-ANOM, ANOVA, regression modelling and SEM fractographic evaluation. The findings indicated that the average fatigue life decreased by about 44% in AA2024-T6 and 39% in AA2024-T3 by increasing stress levels from 320 to 340 MPa. All test conditions showed that AA2024-T3 performed better than AA2024-T6 by about 7-18%, which means that there is a more favourable fatigue response in T3 relative to T6 despite the traditional advantage of static strength of T6. ANOVA confirmed stress amplitude to be the primary factor, with 97.01% and 93.90% contribution to fatigue-life in T6 and T3, respectively. The percentage contribution of frequency was only 2.40 and 4.12 in T6 and T3, respectively. Regression models were found to be highly predictive, and the R2 of both models was found to be 0.9979 and 0.9966, respectively, with the confirmation-test deviations of 5.07%-7.02%, respectively. The results determined AA2024-T3 as the most fatigue-resistant temper among the high-cycle regimes explored.