Abstract
In the super-long life regime, the fatigue behavior of as-extruded Mg-6wt%Zn-xY-0.8wt%Zr Mg alloys with Y content of 0, 1, 2 and 3 wt% have been investigated, respectively. The result indicated that for all measured S-N curves, a plateau existed in the regime of 5×106-108 cyc, and then the fatigue strength gradually decreased between 108 and 109 cycles. Therefore, only fatigue strength corresponding to 109 cycles can be determined. Compared with other alloys, the alloy with Y content of 2 wt% has the highest fatigue strength and its value is 105 MPa. SEM observations to fracture surfaces revealed that for all alloys, the fatigue crack mostly initiated at the surface or subsurface of samples failed within 106-109 cycles. Further observation indicated that the crack initiation was related with activated slip bands instead of phase particles and activated twins. Based on the measured results and Murakami equation, it demonstrates that the fatigue strength of alloys is more dependent on the hardness values.
Highlights
Magnesium alloys are currently used in cars for low stress applications such as covers and less frequently for the mechanically loaded structural components such as wheels, transmission housings and pedals [1]
The fatigue strength of as-cast Mg alloys corresponding to 109 cycles is generally about 40-50 MPa [1]
It can be seen that for all measured S-N curves, a plateau exists in the regime of 5×106-108 cyc, and the fatigue strength gradually decreases between 108 and 109 cyc
Summary
Magnesium alloys are currently used in cars for low stress applications such as covers and less frequently for the mechanically loaded structural components such as wheels, transmission housings and pedals [1]. Defects such as casting porosity and cavities are usually present and the fatigue properties are affected significantly by their shape and dimension [1,2]. Several material defects such as casting porosity, oxidation films and intermetallic inclusions, can act as crack initiation sites and reduce material’s fatigue strength in the super-long fatigue life regime [1,2]. As for the ultra-high cycle (107-109 cyc) fatigue behavior of wrought Mg alloys, only a few research papers can be referred [6,7,8]. It can be predicted that the change of Y content should have some effect on the fatigue behaviour of
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