The influences of extrusion and equal channel angular pressing (ECAP) processes on the fatigue behavior of AM60 magnesium alloy

The fatigue behavior of AM60 magnesium alloy produced by equal channel angular pressing (ECAP) process was investigated by means of fatigue life (S-N) and fatigue crack propagation rate tests. The grain structure of the material was refined from 19.2 mu m to 2.3 mu m after 6 passes of ECAP at 220 degrees C. The yield stress (YS) and ultimate tensile strength (UTS) of the alloy increased to their peak values after two passes but decreased with any further pressing, although the grain size became finer with increasing the number of passes. This is owing to the fact that the softening effect caused by texture anisotropy overwhelmed the strengthening effect due to grain refinement. The texture together with the plasticity-induced crack closure were also the main factors influencing the crack growth rate of the ECAPed Mg alloys. A large enhancement in the fatigue lifetime was also achieved after the 2nd pass of ECAP. This result was remarkable because the improvement was obtained for both the low and high cycle regimes. The present research work has shown that two passed AM60Mg alloy was better than the multi-passed material in view of the fatigue performance. (C) 2012 Elsevier B.V. All rights reserved.