Study On The Grain Refinement Mechanism Of Ultra-fine-grained Aluminum Alloy Prepared By Upsetting And Extrusion Combination

The content of the aluminum element in 1060 aluminum alloy which is close to the pure aluminum alloy has reached up to 99.635 %.6061 aluminum alloy belongs to Al-Mg-Si series alloy,which has been widely used in fields of auto manufacturing market and aerospace fields.7003 aluminum alloy belongs to Al-Zn-Mg-Cu series alloy,which has been widely used in fields of refrigerant containers,cryosurgery tools,military equipment and so on,because of its excellent welding properties and elastic resistance.The principle of cyclic equal channel compression(CECC)is to combine the equal channel angular pressing(ECAP)and muti-axial compressing(MAC).Three newly CECC routes were designed,which are MAC+MAC+ECAP(MME),MAC+ECAP+MAC(MEM)and MAC+ECAP+ ECAP(MEE),respectively.There were 3-pass,one circle of extrusions in total.Furthermore,a new circle of CECC deformation was added on the mentioned condition,which w ere 6-pass,two circles of extrusion s.The route Bc and route C were chosen in the ECAP period.Materials used in the experiment are 1060,6061 and 7003 aluminum alloys.The grain refinement mechanism of aluminum alloy was researched through the analysis of DEFORM finite stimulation,mechanical properties,transmission electron microscope,selected area elect ron diffraction and X-ray diffraction.The results show that:(1)The DEFORM finite stimulation results show that the equivalent stress,equivalent strain and damage value of 6061 aluminum alloy are relatively high after 6-pass of CECC deformation.The load in the MAC period is 6 times higher than the ECAP period.(2)The grain size of two circles,6-pass of MEM-processed(route Bc)1060 aluminum alloy has refined to 0.8?m ~1.5?m from 20?m~36?m after being homogenized anneal ed before deformation.The grain size of two circles,6-pass of MEM-processed(route Bc)6061 aluminum alloy has refined to 0.9?m~1.8?m from 18?m~28?m after being homogenized annealed before deformation.The grain size of two ciecles,6-pass of MEM-processed 7003 aluminum alloy has refined to 750nm~900nm from 16?m~24?m after being homogenized anneal ed before deformation.The grain size of 7003 aluminum alloy was the tiniest and the grains have refined to the nanoscale.(3)The secondary-phase particles of 106 0 aluminum alloy are the fewest.The main secondary-phase particles of 6061 aluminum alloy are Mg 2Si.The main secondary-phase particles of 7003 aluminum alloy are Mg Zn2 and Al2Mg3Zn3,which are the most compared to 1060 and 6061 aluminum alloys.The shape of the secondary-phase particles was changed from the long needle to the short rod,and the secondary-phase particles were distributed homogeneously in the grains and grain boundaries after one circle,3-pass of CECC.At the same time,it was found that the secondary-phase particles had the pinning effect on the grain boundary,which may hinder the grain growth and in consequently,would promote the grain refinement.(4)The dense dislocation walls,dislocation cells and dislocation tangle zones were observed in the aluminum alloys with the increase d passes during the CECC deformation.The dislocation walls would transform into the sub-grains with the increase d strain.Dislocations were further accumulated and annihilated at the sub-grain boundaries,which made the sub-grain boundaries gradually transformed into the real grain boundaries.The low-angle grain boundaries decreased while the high-angle grain boundaries increased.The grains of aluminum alloys were continuously refined.Under the the pinning effect of secondary-phase particles and dislocations segmentation,the grains of aluminum alloys were significantly refined.