Fintová Stanislava, Trško Libor, Chlup Zdeněk, Pastorek Filip, Kajánek Daniel, Kunz Ludvík
Institute of Physics of Materials, Czech Academy of Sciences, Žižkova 22, 616 00 Brno, Czech Republic.
Research Centre, University of Žilina, Univerzitná 8215/1, 010 26 Žilina, Slovakia.
Materials (Basel). 2021 Oct 20;14(21):6245. doi: 10.3390/ma14216245.
Fatigue tests were performed on the AZ91 cast alloy to identify the mechanisms of the fatigue crack initiation. In different fatigue regions, different mechanisms were observed. In the low and high cycle fatigue regions, slip markings formation accompanied with MgAl particles cracking were observed. Slip markings act as the fatigue crack initiation sites. The size and number of slip markings decreased with decreased stress amplitude applied. When slip markings formation was suppressed due to low stress amplitude, particle cracking became more important and the cracks continued to grow through the particle/solid solution interface. The change of the fatigue crack initiation mechanisms led the S-N curve to shift to the higher number of cycles to the fracture, demonstrated by its stepwise character. A lower fatigue limit of 60 MPa was determined at 20 kHz for 2 × 10 cycles compared to the 80 MPa determined at 60 Hz for 1 × 10 cycles.
对AZ91铸造合金进行了疲劳试验，以确定疲劳裂纹萌生的机制。在不同的疲劳区域，观察到了不同的机制。在低周疲劳和高周疲劳区域，观察到伴随MgAl颗粒开裂的滑移线形成。滑移线作为疲劳裂纹萌生部位。随着施加应力幅值的降低，滑移线的尺寸和数量减少。当由于低应力幅值而抑制滑移线形成时，颗粒开裂变得更加重要，裂纹继续通过颗粒/固溶体界面扩展。疲劳裂纹萌生机制的变化导致S-N曲线向更高的断裂循环次数偏移，这通过其阶梯状特征得以证明。与在60Hz下1×10⁶循环时测定的80MPa相比，在20kHz下2×10⁶循环时测定的疲劳极限为60MPa。
