Fracture toughness and high-cycle fatigue behaviour of Al-Mg and Al-Mg-Sc-Zr alloys

Tensile, fracture toughness and high-cycle fatigue tests were carried out on Al-Mg and Al-Mg-Sc-Zr alloys. Fracture morphology and the microstructure of the alloys were observed by SEM and TEM, etc. Al-Mg-Sc-Zr alloy with fibrous fine grain structure showed higher tensile strength and fracture toughness than Al-Mg alloy, which had a larger grain size and obvious recrystallisation. In high-cycle fatigue tests, Al-Mg-Sc-Zr alloy presented a higher fatigue limit owing to its finer grains and nanosized precipitates, which increased the difficulty of fatigue crack initiation. Al-Mg alloy presented a lower fatigue limit because crack initiation caused by slip is more likely to occur. However, its rougher fracture surfaces may be beneficial to hindering the propagation of macrocracks.