Study On Microstructure, Mechanical Properties And The Difference Of Stacking Fault Energy In Cu By Equal Channel Angular Pressing

The ECAP (equal channel angular pressing) not only can prepare the bulk ultra-fine grained (UFG) materials effectively, but also improve the comprehensive mechanical properties by severe plastic deformation. The microstructure evolution and strengthening mechanism of material with different structural feature is distinct via ECAP. Pure copper, face-centered cubic structure, was selected as the main experiment subject. Microstructure evolution, macroscopic grain orientation and mechanical properties were investigated in the light of the dislocation density via ECAP. The aluminum and copper, which possess distinct stacking fault energy, were discussed in aspect of structure characteristics and the transformation of mechanical capacity during ECAP. The conclusions of this paper are listed as follows:(1) The copper was processed via ECAP to8passes, grain size refined below5μm using route A and into5-10μm using route Be from60μm of as-cast.(2) The paths make a difference in the variation trend of macroscopic grain orientation in the course of ECAP. The fluctuation of the diffraction intensity showed strongest by route Be far outstrips that of route A, which incarnate that the process of microstructure homogenization.(3) After eight passed of ECAP, the vickers hardness were increased from65.2HV to160HV by route A and boost into142HV by route Be. The tensile strength was remarkable increased from220MPa to448MPa using route A. The ductility of copper after ECAP, however, was seriously reduced. Elongation reduced from55.3%to15%in immediately after1pass via route A, and later keeping fluctuating, finally regained to some extent. The elongation percentage of Be path,23.2%after8passes, is higher than A path, which indicate that during the ECAP process, the strengthening mechanism of the ECAPed copper is coupled with fine-grain reinforcing and dislocation reinforcing.(4) The dislocation density of route A is0.38×1014m-2after4passes from0.1×1014m-2, which increased remarkably with the passes increase and reduced in the later stage. And for route Be, the values present large undulation, which reached0.3×1014m-2after8passes.The differences exhibit above attribute to the variation of shearing plane direction and shear strain in different paths. During the extrusion of A path, whose strain was stacked effectively and dislocation propagate rapidly, the refining effect of grain is significant. The shear plane of adjacent passes in Bc paths is diverse, which triggered more slip systems, the annihilation and recombination of dislocation lead to the masses of equiaxed grain. Therefore, the strengthening effects of A path is superior to Bc path.(5) By means of macro and micro fracture morphology analysis of tensile specimen, it incarnate the cup and cone morphology with increased shallow dimples amounts and more uniform distribution that revealed the homogenization of microstructure and its ductile fracture mechanism.(6) By means of microstructure evolution and mechanical property analysis of different metals, which possess diverse stack fault energy(SFE), pure copper, middle SFE metal material, acquired the characteristic of high and low stack fault energy.