Fatigue fracture behavior of Mg-Zn-Y alloy

Recently, Mg-Zn-Y alloys with superior performance, which have a long period order (LPO) phase, have been developd. Therefore, it is important to understand fundamental fatigue properties in such materials. In this study, the fatigue fracture behavior of Mg-Zn-2-Y-2-Zr-0.2 alloy has been investigated using a plain fatigue bending, testing machine, which Was originally developed for thin sheet specimen. One end of the sheet specimen is fixed at a voice coil of the loudspeaker and the other end is set free. A bending mode resonance occurs in the specimen due to forced vibration at the fixed end. To estimate stress amplitude of bending. deflections Lit the free end of the specimen oscillating at a frequency of about 250 similar to 700Hz was measured by a laser displacement gauge. For comparison, AZ31B alloy also has been investigated. S-N curve for the Mo-Zn-2-Y-2-Zr-0.2 alloy was obtained using a stress ratio of R=-1, and the fatigue strength was estimated as about 200MPa at 10(6)similar to 10(8) cycles. The value corresponds to about 50% of 0.2% proof strength of the alloy. Two types of fatigue surface were observed in the alloy. One is striation like pattern and the other is relatively flat surface. The former is similar to fatigue surface of AZ31B. Therefore, these two types Of fatigue surface cot-respond to crack passing through alpha-Mg phase and LPO phase. respectively.