Study On The Consolidation Mechanism Of Pure Aluminum Powder Materials During Equal Channel Angular Pressing

Equal channel angular pressing of the powder metallurgy material is the perfectcombination of plastic deformation technology and powder consolidation technology. Inthis paper, pure aluminum powder consolidation behavior and consolidation mechanismunder ECAP process were studied. Through the ECAP experiment of aluminum powderand fracture analysis, the test of the microhardness, the measure of the relative density,to evaluate the quality of powder consolidation. The software Deform was used forthermodynamic coupling finite element simulation analysis of the aluminum powderECAP process. The powder deformation stage, the equivalent stress and strain, thedensity, the force and temperature distribution were studied to analyze the consolidationbehavior of aluminum powder from the macroscopic angle. Molecular dynamicsmethod was used on the pure aluminum at different temperature, different pressure andunder the condition of the ECAP to simulate the diffusion behavior, from the nano angleview of the relationship between diffusion and energy to analysis the consolidationmechanism of aluminum powder.Experimental result showed that, pure aluminum powder could be consolidatesuccessfully into full dense bulk material at200℃using ECAP. Compression fractureSEM morphology showed that fracture surface was smooth, fracture surface presentsdimple characteristics, the values of the microhardness and relative density of thealuminum powder were close to the values of casted aluminum and sintered aluminumunder the ECAP, so the consolidation effect was ideal. Based on the compressiblecontinuous medium theories, thermodynamic coupling finite element simulation of thealuminum powder ECAP process showed that, the hydrostatic pressure of the sampleachieved maximum when it passed through the intersection part, the contact area of thepowder particles can be sufficiently increased and break the oxide layer. There is asignificant effect of shear heating at the intersection part, resulting in the temperaturereached to the peak. It was found that ECAP had a significant effect on the strainaccumulation, the largest equivalent strain was about1.4. The relative density couldreach to0.97, almost fully dense material, provided favorable conditions for the powderconsolidation. The consolidation was completed after the powder passed through theeffect of the shear zone. The diffusion study of the molecular dynamics showed that, theECAP unique high temperature field increased thermal motion of the aluminum atoms. High pressure force field could reduce the atomic diffusion distance, which providedfavorable conditions for aluminum atom diffusion. The ECAP deformation process wasconducive to the occur of the diffusion, so the powder could be consolidation under thecondition of low temperature.