Homogeneous consolidation process by ECAP for AZ31 cutting chips

Experiments have been conducted on AZ31B magnesium alloy cutting chips in order to investigate the feasibility of producing a compaction with homogeneous mechanical properties at room temperature using equal channel angular (ECA) pressing. Repetitive pressings, consisting of a total of 4 passages through a die at 573 K with and without MoS₂ as a lubricant, were conducted on each sample. After the initial pressing of each sample was completed the samples were rotated 90 degrees and pressed again. This pressing procedure was repeated two more times for all four samples. It was shown that ECA pressing without lubricant was capable of obtaining the compaction with crack free smooth surfaces after a single pressing. This was most likely because after pressing, a thin, continuous surface layer is created by the heavy shear strain caused by the resulting friction constraint from the die surface. The FEM analysis confirmed the heavy shear strain distribution in the surface layer of the compaction after the single pressing without lubricant. Grain refining after the pressing was observed via the TEM. However, the mechanical properties at room temperature were not homogeneous even after repetitive pressings up to a total of 4 passages through a die. Contrary to the non lubricated samples, samples that were ECA pressed using lubricant did not display the thin shear strained surface layer. The lack of the distributed shear strain surface layer was most likely caused by a lower coefficient of friction created by the MoS₂ lubricated die. Experimental procedures also concluded that the pressing force required for the lubricated samples was remarkably low in comparison with that for the non-lubricated pressings. However, surface crack formation could not be avoided during the pressings that utilized the lubricated ECA pressing process. It was shown that a combined ECA pressing process consisting of an initial pressing without lubricant followed by repetitive pressings up to a total of 3 passages with lubricant was an effective method for producing a compaction with homogeneous mechanical properties at room temperature under low pressing force.