Two-way And Other Channels To The Preparation Of Ultrafine Grained 6061 Aluminum Alloy

Grain refinement,which can improve the strength and the toughness of plastic materials without changing any components of materials,is one of the most effective ways to improve the overall performances of materials. Ultrafine grain materials (grain size of 10nm-1000nm) with excellent mechanical, physical and plastic properties play the important role of civil and national defence products. Severe plastic deformation(SPD) method is one of many methods to make materials of ultrafine grains. Bulk ultrafine-grained materials are made by SPD method which is payed great attention to the domestic and foreign researchers.SPD method has advantages such as relatively simple processing and low cost.Dual Equal Channel Lateral Extrusion(DECLE) was presented by the author of this paper to refine grains.Samples of 6061 Al alloy were processed for severe plastic deformation by DECLE.Mechanical properties and microstructure of samples were characterized.The results of the experiments are listing as following:(1) 6061 Al alloy with average grain size of 400nm were prepared by two passes of DECLE.However,the average grain size of original samples is about 60μm-80μm at room temperature.(2) The microhardness, tensile strength and yield strength of samples in deforming state is 50.6Hv,156Mpa and 151Mpa respectively.However, the microhardness, tensile strength and yield strength of original samples is 27.2HV, 119MPa and 98Mpa respectively.(3) The ultrafined grains was retained in the 6061 Al alloy up to the annealing temperature as high as 180℃for 1 hour. The average grain size of samples failed to increase, and has the trend for further refinementResults and discussionsThe microhardness, tensile strength and yield strength of SPD samples prepared by DECLE are increased remarkably.The grain size is refined and stable in annealing state. When original equiaxed grains are deformed, there are two directions of shear deformation.In the same time, there are two effects of squeezing and compressing.A large number of dislocations were appeared after grains are flattening and shearing,which gradually formed the dislocation walls and cells with the strain cumulation, at last high-angle and small-angle grain boundaries were formed.Thus the grain size decrease.In summary,6061 aluminum alloy of ultrafine grains can be prepared by DECLE with less passes of processing which mechanical properties are improved.