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Experimental Study on Multipass Equal Channel Angular Pressing of Pure Al Sintered Material

Author: HuangKeShuai
Tutor: LiPing
School: Hefei University of Technology
Course: Materials Processing Engineering
Keywords: pure Al sintered material powder in tubes- equal channel angular pressing structure and properties refinement and compaction
CLC: TG376
Type: Master's thesis
Year: 2009
Downloads: 44
Quote: 1
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Abstract


This paper combined the characteristic of powder plastic with equal channel angular pressing(ECAP), put forward a new technology called powder in tubes- equal channel angular pressing(PITS-ECAP). Pure aluminium sintered material was successfully experienced ECAP of multiple passes. The structure and properties before and after deforming were studied. The main point of the paper was to investigate the evolution of microstructure and properties during pressing of different routes. The refining and compacting mechanics of powdered material during the pressing has been discussed. Based on the mentioned above research, pure aluminum powder particles were successfully synthesized into high dense bulk fine-grained material directly by PITS-ECAP.It shows that initial coarse equiax grained microstructure with relative density 0.88 and mean grain size 46.8μm turned to fully dense ultra-fine grained microstructure with mean grain size about 1.5μm after four pressing under route BC. The microhardness increased from 24.5 kg/mm2 to 50.9 kg/mm2, the yield strength increased from 41MPa to about 120MPa. The refining results after using route BC and A were better than that after using route C.In this study, the evolution of microstructure in plane X and Y after each pass of different route was observed. The shear characters of three routes were analysed according to the cube element torsion model. The microhardness distribution of the different passes of the cross-section of workpiece for different routes shows the distribution after one pass is not uniform, but will be more uniform with the pass increased. The route BC can get a better distribution than route C and A.Through TEM observation of deformation sample after each pass of route BC, considering the grain refinement effect in PITS-ECAP depends on some key factors such as hydrostatic stress, strain value and shear deformation character. The initial coarse grains shear deformation and formate high density dislocation, then dislocation transformate to dislocation cells and walls, formatting fine subgrains with micrometer. It is considered that large shear plastic deformation and high hydrostatic stress state are the key factors for materials to obtain a high density material in PITS-ECAP process through pore closing simulation experiment. The pressing route has a main effect on the deformation of pore and the densification effect of powdered material in multipass pressing.Based on the experiment above, pure aluminum powder particles were successfully synthesized into high dense bulk fine-grained material(relative density 94.5%, mean grain size 12.3μm) directly by powder in tubes-equal channel angular pressing (PITS-ECAP) at 150℃. The deformation temperature is below the sintering temperature so much. The hardness and yield strength increased into 45.7 kg/mm2 and 74.9 MPa after pressing, which are much higher than that of commercially pure aluminium and sintered body.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metal pressure processing > Extrusion > Extrusion process
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