The axial fatigue tests were conducted using Al-Mg-Si casting Al alloys with some impurity chemical compositions to investigate the effect of impurity chemical composition on the fatigue behavior. The simulated impurity chemical compositions were Fe, Mn and Ni. The effect of weight% of Fe was also investigated by changing Fe content. By adding impurity chemical compositions, intermetallic compounds (IMCs) were formed in the matrix, while the size and distribution of IMCs were similar to those of eutectic Si. When the weight% of Fe exceeded 1.5%, long IMCs with high aspect ratios were formed. The effects of impurity chemical compositions on the static mechanical properties, such as 0.2% proof stress, tensile strength and hardness, were small. However, samples with 1.5% and 2.0% Fe exhibited higher proof stress and hardness. The fatigue strengths of the samples with impurity chemical compositions were higher than those of the standard samples. When the weight% of Fe exceeded 1.0%, some samples showed lower fatigue strengths than the standard samples. In those cases, large IMCs were found at the crack initiation sites, which reduced crack initiation resistance and shortened fatigue lives.
