Growth behaviour of small cracks in Al-Mg-Si alloy with strain-aging nature

Abstract

The purpose of this study is to clarify the effect of solute Mg on fatigue strength characteristics. The high-cycle fatigue properties of an Al-Mg2Si quasi-binary alloy (6061) and a modified alloy containing excess solute Mg are compared in terms of the growth behavior of initial small cracks. A distinct knee point (fatigue limit) and coaxing effect controlled by a (quasi) non-propagating crack appear only in the case of the modified alloy with a surface defect. The growth resistance of such a small crack is found to be significantly higher than that of a longer one. These results may be attributed to the strain aging characteristic of the modified alloy.