The Study Of Microstructure And Properties Of Commercial Pure Aluminum By Continuous Variable Cross-Section Recycled Extrusion Technique

The shape and technology parameters have significant effect on formability,metal flow rules,microstructure and properties of samples after deformation when plastic deformation act on metals.The deformation technology,transformation law of microstructure and peoperties of bulk as-cast commercial pure aluminium 1A85 processed by Continuous Variable Cross-section Recycled Extrusion(CVCE)technology was studied,providing reliable throretical and experimental evidence for optimizing CVCE technique and producing fine grain materials.CVCE deformation process was finished through designing CVCE composit die.The effect of CVCE technological parameters on formability,microstructures and properties of metal was investigated.The main contents and results of this paper are as follows:The influence of extrusion angle and original sample Height-Diameter ratio on external morphology and internal metal streamline were investigated.The results shows that: When extrusion angle is 6° ~ 7° and primary specimen Height-Diameter ratio is 1.83,not merely is better cyclic extrusion and recovery effect easier obtained,but also the product with better-quality surface can be gained and uniform metal flow line can be ensured in the meanwhile.Metal flow rules after CVCE deformatuion indicates that: The flow velocity of outer metal was fater than that inside of after deformayion samples.The combined effects of both the metal partical flowing along the radial and its flipping along the height lead to increasing top surface area of samples after upsetting by CVCE technology,which gradually permeates from the upper to the lower.Decreasing of each layer for samples also reduces from the upper to the lower because of the transmission effects of deformation that samples were compressed in vertical direction.The effects of extrusion angle on microstructure and properties were researched and results reveal that: the grain refinement of 7° was more severe than 6°.Microhardness increased to 105.62 HV after 3 passes,which was increased by 4 times compared with riginal sample.Microstructure and properties distribution characters along height,thickness and width direction of 7° samples were further studied.It can be founded that deformation degree was different in diverse position of samples due to different stress condition in each direction.The grain size gradually increased from surface to center along the thickness and height direction,while the change of microhardness opposite to the grain size which was in line with refined crystalline strengthening theory;the shift of grain size from surface to the center along the width direction was unconspicuous.The influence of deformation passes on microstructure and properties were studied.It can be seen from the result that: With the deformation passes increasing before 4 passes,the dislocation density increased and dislocation moved from the inside to the boundary of grains and then dislocation cells formed through dislocation tangled and piled up.Meanwhile,a large number of equiaxed grains and HAGB produced.A large number of refined grains distributed homogeneously and grain sizes were fully refined to 0.4?m which is 1/210 of original grain size until 3 passes;microhardness increased up to 89 HV and microhardness index was decreased down to 3.1;ultimate tensile strength sharply continuously increased up to 289 MPa from 123 MPa and yield strength to 80 MPa from 57 MPa after 3 passes.