Effect Of Pre-compression Deformation On Low-cycle Fatigue Properties Of AZ31Magnesium Alloy

As the lightest metal structure material, magnesium alloys has been widely usedin the aerospace, automotive and electronics and other fields, which have excellentproperties such as high specific strength, high specific stiffness and good recyclability.Since long-term cyclic stress or strain is imposed during in the service period, themagnesium alloy components are expected to failure in the mode of fatigue fracture.As an important plastic deformation mechanism of magnesium alloys at roomtemperature, twinning will have a great effect on fatigue behaviors. Therefore, it seemsto be very important to study the effect of twins on low-cycle fatigue properties ofmagnesium alloy. This paper studied the low-cycle fatigue properties of AZ31hotrolled magnesium alloy sheet under the constant strain amplitude control, and effect ofinitial twins introduced by pre-compression deformation on the fatigue behavior ofmagnesium alloys. It can draw the following main conclusions:①With the imposed strain amplitude increasing gradually, the cyclicdeformation mechanism of as-received samples changed dominated slip and twinninginto dominated twinning and detwinning. They showed high cyclic hardeningbehaviors under high strain amplitude due to the of accumulation residual twin. Twinsformed continually in the process of fatigue and the number of residual twin increasedsteadily, making the subsequent deformation more and more difficult.②After pre-compression by a strain value5%on transverse direction, thefatigue life of PR samples inceased form1436N to2856N, and PRA samples inceasedto2128N. Due to pre-compression subdividing mother grains into more samll grains,slip become into the dominated cyclic deformation mechanism. Initial twins producedin the pre-compression could not disappear completly in the process of detwinning,making continuous blocks to hinder dislocation slip movement.③After pre-compression by a strain value3%on rolling direction, the fatiguelife of pre-compressed samples was improved, fatigue life increasing nearly three timesespecially when stress amplitude was close to the yield strength. These initial twincan’t completely be eliminated in the cyclic deformation, the remainning twins willrestrain the twinning and detwinning in the subsequent cyclic deformation.