The Preparation Of Nano-Al₂O₃p/2024Composite Material And Repeated Upsetting And Extrusion

In this paper, nano-Al₂O₃p/2024composite was fabricated by the pre-dispersionof ball milling and then nano Al₂O₃p/2024composite materials melt was preparatedby the solid-liquid mixture casting process, and the composite materials melt wastreatmented by high-energy ultrasound. The metallurgical and solidification structureof Al₂O₃p/2024composite material which was preparatd after high energy ultrasoundprocess were studied.After hot extrusion deformation, nanometer Al₂O₃p/2024composite material was deformed by reciprocate upsetting and extrusionprocess.Microstructure evolution was studied by transmission electron microscopy（TEM） and SEM to elucidate the grain refinement mechanism.At last the influencingfacts on the mechanical properties at room temperature were discussed.The as-received nano-powder of Al₂O₃particle was uniformly distributed on thesurface of pure-Al powder after ball milling. The billed nano-Al₂O₃/Al compositepowders were effectively incorporated into aluminum matrix and well dispersed in themelt using solid-liquid mixed casting process. Then the sound pressure produced byhigh-energy ultrasonic and transient impingement could further disperse the tinyclustering of Al₂O₃nanoparticle in the composite slurry, improving the distribution ofnanoparticles in molten matrix. With the increase of the nanoparticle concentration,the degassing efficiency significantly decreased due to the increasing viscosity of thecomposite melt. The high-intensity ultrasonic field was injected into the compositemelt during the solidification, the grain microstructure was effectively refined. Therefinement effection was weaken on the too high or too low ultrasonic temperature.When the ultrasonic temperature was670-650℃, ultrasonic power was300w, thecomposite presented a fine uniform microstructure, which was composed of finegrains with an average size of25μm. Compared with the alloy matrix, the mechaniealproperties of the nano-Al₂O₃p/2024composites were signifieantly increased due tothe nanoparticle addition. When the content of Al₂O₃nanoparticulates was1.0wt.%,the nanocomposite presented the maximum tensile properties. However, with theincrease in the mass fraction of nanoparticles, the tensile strength ofnano-Al₂O₃p/2024aluminum matrix composites gradually decreased. These resultswere attributed that higher content of Al₂O₃nanoparticulates in the matrix would leadto more agglomeration of Al₂O₃particulates.． The alloy matrix was effectively refined after modified RUE processing, and thegrain refining efficiency decreased with the increase of RUE pass number. More RUEpass, the microstructure was more refine and homogeneous. After4passes, the grainsize was effectively refined to between2um and6um. XRD results showed that theorientation of the matrix were changed during RUE deformation, which lead to theincreasing chaos degree of grain orientation. The initial orientation （311） of extrudedcomposite was disintegrated, and the orientation of （111）,（200） and （222） wasweaken, and the orientation （220） disintegrated after pre-hot extrusion were re-appearafter RUE processing.Room-temperature tensile test results showed that the yield strength （YS）,ultimate tensile strength （UTS）, and the elongation （δ） increased with the increase ofRUE pass. The ultimate tensile strength（UTS） and yield strength（YS） of as-extrudednano-Al₂O₃p/2024composite processed after T6heat treatment was485MPa,382MPa and8.5%, respectively. The UTS and YS of as-aged Al₂O₃p/2024compositeprocessed after1RUE pass was492MPa and391MPa, respectively. The UTS and YSof as-heat Al₂O₃p/2024composite processed after4RUE pass was477MPa，375MPa.With the increase in RUE pass, the composite material plastic improve gradually. Theinitial state of composite material elongation rate is only8.5%. The elongation rateincreased to13.5%after5RUE pass.