Evaluation of Possible Life Improvement Methods for Aluminum-Zinc-Magnesium Fillet-Welded Details

Abstract

Fillet welds have a low fatigue resistance compared with other types of weld detail, and it is difficult to design structures without using them. Results are presented of screening tests on methods of life improvement that have been applied successfully to fillet welds in steels under fluctuating tensile loading and are applicable to heat-treatable aluminum alloys. The welding method or shielding gas used did not affect fatigue life: (a) improvement of the weld profile during or after welding resulted in slightly increased lives; (b) local peening treatments had to be sufficiently intense to produce compressive residual stresses some depth below the surface to cause a worthwhile increase in life; and (c) specimen overloading treatments applied both initially and periodically generally were effective but the results for exclusion of the atmosphere by a conventional paint system were inconsistent. Results of tests on as-welded specimens, at various stress ratios which include compression in the loading cycle, corresponded with the results of treatments which include compressive residual stresses. The number of tests of each method was small, and further investigation of the more promising methods is recommended before they can be applied generally without qualifying tests.