The current work investigated the effect of shot peening (SP) on high cycle fatigue (HCF) behavior of the hot-extruded ZK60 magnesium alloy. SP can significantly improve the fatigue life of the ZK60 alloy. After SP at the optimum Almen intensities, the fatigue strength at 107 cycles in the as-extruded (referred to as ZK60) and the T5 aging-treated (referred to as ZK60-T5) alloys increased from 140 and 150？MPa to 180 and 195？MPa, respectively. SP led to a subsurface fatigue crack nucleation in both ZK60 and ZK60-T5 alloys. The mechanism by which the compressive residual stress induced by shot peening results in the improvement of fatigue performance for ZK60 and ZK60-T5 alloys was discussed. 1. Introduction The weight reduction of automobiles is one of the most effective ways to improve fuel consumption since the resistance of a vehicle to rolling, climbing, and acceleration are directly dependent on the vehicle mass. Therefore, the application of magnesium alloys which have the density only roughly 25% of that of steel and 66% of that of aluminum is expected to increase substantially in this decade [1, 2]. For these automotive components under the combined actions of fluctuating loads and corrosive environment, good high cycle fatigue (HCF) performance must be achieved. However, in comparison to aluminum alloys and steels, the research results on fatigue properties of magnesium alloys are still limited. Some research has shown that the fatigue properties of magnesium alloys are poor [3, 4], thus making it difficult to apply the alloys for load-bearing parts in automobiles. Therefore, the improvement of the fatigue properties of magnesium alloys becomes a vital research subject. Considering the fact that crack initiation of magnesium alloy is a surface phenomenon controlled by aspects as residual stress level near the surface, the existence of compressive residual stresses in surface region results in an improvement of fatigue properties [5, 6]. Shot peening (SP) is a powerful method to enhance the fatigue performance of structural metallic materials, and some investigations on the influence of shot peening were performed on the Mg-Al alloys AZ31, AZ80 [7, 8], and A8 [9]. The results demonstrated that SP effectively improved the fatigue properties of magnesium alloys [7–9]. However, bombardment of the surface with the shot often leads to the initiation of flaws or cracks, whose detrimental effect on strength may outweigh the beneficial effect of the compressive residual stresses. Thus, for magnesium alloys, care must be taken to optimize the peening
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