Fatigue properties of Al-Mg alloys with and without scandium

The fatigue properties, e.g. HCF strength, crack growth of small surface and long-through cracks, of two wrought Al-5Mg-0.3Mn-0.06Zr alloys without and with scandium (0.25%) were investigated in vacuum, air and salt water. The alloy with scandium showed a higher tensile yield stress, higher fatigue strength values and a higher resistance against microcrack growth, due to the presence of coherent Al3 (Sc, Zr) precipitates and a very fine subgrain structure. The scandium free alloy exhibited a slightly higher resistance against macrocrack growth, due to the coarser grain structure.