Microstructures And Mechanical Behaviors Of Mg-Mn-Zn-Ce Alloy Subjected To Equal Channel Angle Pressing

The ultrafine materials produced by equal channel angle pressing (ECAP) exhibit the good properties, and is paid much more attention by the scientific world. The corresponding researches have been well documented for the f.c.c metals, but the less researches have been conducted for the f.c.p metals especially for magnesium alloys. In this dissertation, the microstructures, tensile properties and low cyclic fatigue behavior of Mg-Mn-Zn-Ce alloys subjected to equal channel angle pressing have been studied. In addition, the morphologies of the fracture surface after both tensile and low cyclic fatigue experiments are observed using scanning electron microscope (SEM) for the ECAPed Mg-Mn-Zn-Ce alloysThe observations of microstructures show that for the Mg-Mn-Zn-Ce alloy, the average grain size is about 11μm after one pass of ECAP, and about 2μm after two passes of ECAP.The results of the tensile experiments indicate that the ultimate tensile and yield strengths of the ECAPed Mg-Mn-Zn-Ce alloys get remarkably enhanced with increasing the pressing pass. The elongation of the Mg-Mn-Zn-Ce alloy increases a little after one pass of ECAP while decreases significantly after two passes of ECAP, especially in route A.The results of low-cyclic fatigue tests reveal that the fatigue life of the Mg-Mn-Zn-Ce alloys is closely related to the both pressing pass and pressing route, where the alloy subjected to two passes of ECAP with route C gives the longest fatigue life. At the higher total strain amplitudes, the alloys subjected to ECAP with different pass and route exhibit cyclic strain hardening, while at the lower total strain amplitudes, the alloys show stable cyclic stress response or cyclic strain softening. For the Mg-Mn-Zn-Ce alloys ECAPed by different pass and route, the relation between elastic and plastic strain amplitudes with reversals to failure shows a monotonic linear behavior, and can be described by Basquin and Coffin-Manson equations, respectively. The cyclic stress-strain relation of the Mg-Mn-Zn-Ce alloy ECAPed for one pass shows a monotonic linear behavior. But the cyclic stress-strain relation of the Mg-Mn-Zn-Ce alloys subjected to two passes of ECAP show different behavior, that is, a bilinear behavior for the alloy ECAPed by route A, and a monotonic linearbehavior for the alloy ECAPed by routes B_C and C.The SEM observation on the fracture surfaces show that under the tensile loading condition, the ECAPed Mg-Mn-Zn-Ce alloys exhibit ductile fracture, while under the low cycle fatigue loading condition, the fatigue cracks initiate transgranularly at the surface of samples and propagate in a transgranular mode.