Research On The Racheting Of Rolling Magnesium Alloy And The Microstructure Simulation

As the lightweight structural material, magnesium alloys have been widely used in communication, transportation and aviation industry. These components are often subjected to variable amplitude loading, non-symmetrical cyclic stress or strain conditions. So in addition to a higher specific strength and specific stiffness, also requires a smaller cycle strain. Ratcheting is the characterization of the accumulation of plastic strain in the cycle fatigue. Research on ratcheting can effectively prevent excessive size failure or damage which due to the plastic deformation.In this paper, the unidirectional hot rolling was applied to prepare AZ31 magnesium alloy sheets. The microstructures, static mechanical properties and ratchetings of the sheets were obtained with different reduction rates and angles. A polycrystal model which based on Voronoi figure with [0,1] fixed boundarys was built to simulate the variation of ratcheting behaviors and microstructures.The results shown:1) After rolling, twins were appeared in AZ31 magnesium alloy sheets. There were more twins and the grain size was smaller with the increase of reduction rate. Besides, the strength increased, and the elongation decreased. The anisotropy was obvious. The strength was higher when the angle was 90°while the elongation was smaller when the angle was 0°.2) Similar to the as-extruded AZ31 magnesium alloy, cyclic hardening occurred in the rolled sheets. The ratcheting strain of AZ31 magnesium alloy increased with mean stress and stress amplitude.The mean stress determined the level of the ratcheting strain, the stress amplitude determined the range of the deformation and the peak stress was the motive power of ratcheting.3) The cyclic hardening ability of sheets were better with the increase of reduction rate. The ratcheting strain was smaller when the angle was 45°. The ratcheting strain was determined by reduction rate and angle. The samples premature broke when the reduction rate was 45% and the angle was 0°.4) In the polycrystal model, a negative exponent relationship existed between the average relative grain size and the grain number. The results of the numerical simulation were similar to the practical ratcheting test. The stress and strain distribution of the polycrystal model was determined by the stress outside and the grain orientation inside.