Improving The Fatigue Performance Of Welded Aluminum Alloys

Author:  Montemarano, T.W. and Wells, M.E.
Source:  Report No. DTNSRDC/SME-78/66
Doc ID:  1979002
Year of Publication:  1979
Abstract:  
A program was undertaken to develop methods for improving the fatigue performance of welded 5086-H116 alloy aluminum for surface effect ship construction. Of the methods investigated, postweld brush shot peening was found to offer the best improvement. Shot peening studies were conducted using two types of commercially available peening brushes. The effect of peening parameters on peening intensity was determined. Fatigue test results showed that peening intensities of 0.0035 to 0.0080 inch significantly improved the fatigue performance of 5086 butt and fillet weldments. The fatigue strength of 5086 butt welds was improved to the level of unwelded base metal, and the fatigue strength of 5086 fillet welds was increased from 5,500 to 10,000 pounds per square inch at 10 million cycles. The wide range of optimum peening intensities makes the brush peening process relatively insensitive to operator error. Based on the fatigue results, brush shot peening was applied to weld repaired fatigue cracks on the surface effect ship, SES-100A, and was successfully performed on irregular weld surfaces in areas of limited accessibility. Due to the significant improvements in fatigue performance of welded 5086 and the relative insensitivity of fatigue life to operator process variables, rotary brush peening should be considered a potential method to be used in aluminum hull construction for postweld.