<p>In this investigation, the effect of sheet thickness on the fatigue performance of friction stir welded AA2014-T6 joints was studied. The joints were fabricated using sheets of 2, 3, and 4&#xa0;mm thickness. All three joints were observed to be defect-free. The fatigue tests were carried out at a stress ratio of <i>R</i> = 0.1 and a frequency of 10&#xa0;Hz. From the test results, the 2&#xa0;mm thick sheet showed better fatigue performance than its counterparts. The maximum fatigue strength of 55&#xa0;MPa at 2 × 10⁶ cycles was observed for the 2&#xa0;mm thick joint. The higher fatigue strength was attributed to the formation of second-phase particles such as Al₇Cu₂Fe and Al₂₀Cu₂Mn. These precipitates help in the refining of the grains and enhancement of the fatigue strength. Furthermore, the enhancement in strength was mainly due to the presence of fine and recrystallized grains in the weld region. From the results, the joint welded with a 2&#xa0;mm thick sheet showed higher fatigue strength than the others. This may be attributed to the combined effect of recrystallized grains, fine distribution of second-phase particles and optimum heat generation in the weld region.</p>