3539 - INFLUENCE OF SCANDIUM ON THE KINETICS OF FATIGUE CRACK GROWTH IN 7010 AL – ALLOY

The Influence of Scandium (Sc) addition on the fatigue crack growth rate and the fatigue crack threshold has been examined in the 7010 Aluminum alloy. The base line 7010 Aluminum alloy has been modified with Scandium addition and then subjected to a peak aging, T6 condition of heat treatment. The fatigue testing was done on a 858MTS servo hydraulic machine at a frequency of 40Hz and a stress ratio of 0.1. The fatigue crack growth study was conducted at constant amplitude loading. The threshold stress intensity factor ∆Kth was evaluated using the standard load shedding technique in both the conventional 7010 alloy and the Sc treated alloy. The fatigue crack growth rate da/dN versus stress intensity range ∆K curves were plotted and the Paris constants were obtained. The microstructural studies were conducted and the fracture surface study was done using Scanning electron microscopy. The investigations revealed that the Scandium addition refines the grain structure but exhibits poor fatigue crack growth resistance, as well as a lower value of ∆Kth. The results have been discussed in the light of microstructural observations.