Study On The Influence Mechanism Of Thermomechanical Treatment On The Microstructure And Properties Of A New Al-Cu-Mn Alloy

For age-hardenable alloy,the processing technology experienced has a great influence on the final performance.Thermomechanical treatment is a combination of plastic deformation and heat treatment.It can fully enhance the strengthening potential of the alloy by adjusting the dislocation structure and density,grain size and precipitation characteristics(size,density,etc.)of the precipitated phase.It is a typical and broad Application prospect processing method.The evolution of the microstructure during plastic deformation and subsequent heat treatment is relatively complicated,and the current understanding of the above process is not comprehensive,which makes it difficult for the alloy to obtain ideal performance after thermomechanical treatment.In addition,controlling the aggregation state of alloying elements before deformation and performing warm deformation at the precipitation temperature of the precipitates have an important influence on the distribution of the precipitates and the evolution of the grain structure.Therefore,exploring thermomechanical treatment(combination of solid solution,deformation and aging)is very important to control the microstructure of the alloy and improve its performance.This paper takes a new type of Al-Cu-Mn alloy as an example,mainly studies the microstructure evolution and mechanical properties of the alloy during thermomechanical treatment,and quantitatively analyzes the typical strengthening mechanism by means of TEM,SEM,XRD,etc.Reveal the microscopic mechanism of alloy performance improvement.The main conclusions are as follows:(1)The effect of the solution and aging process on the properties of the aluminum alloy is: with the increase of the solution temperature or the extension of the solution time,the number of undissolved phases in the original cast T6 alloy gradually decreases,and the solution temperature and time Taking 540 ℃ and 14 h as the boundary,the strength and plasticity showed a trend of increasing first and then decreasing.TEM results show that there is a rod-shaped T phase with a size of about 200 nm in the matrix in this state,that is,an appropriate amount of undissolved second phase can improve the mechanical properties of the alloy.During the aging process,according to the TEM image of the 160 ℃×10 h strong plasticity matching sample,it can be inferred that the alloy was solid-dissolved at 540 ℃ for 14 hours and then cooled in water,then aged at 160 ℃ for 10 hours and then air-cooled to obtain a better structure,relatively best matching of strength and toughness,the highest tensile strength of 478 MPa,and the tensile elongation of 11.8%.(2)The microstructure and properties of the alloy were significantly affected by cold rolling deformation and subsequent aging.With the increase of deformation(maximum deformation ～90%),coarse equiaxed grains are gradually broken and refined after solution,and typical fibrous structures can be gradually formed in the longitudinal section of deformed samples.The phenomenon of grain fragmentation,the remaining T phase after solution treatment plays a certain role in grain refinement in the process of deformation and subsequent aging.When the deformed alloy is aged at a lower temperature,recovery and precipitation occur.With the extension of the aging time,the high-density dislocations gradually formed ultra-fine crystals/nanocrystals with an average size of ～184 nm through violent recovery(slip,climb).The remaining rod-shaped T phase after solution treatment has a certain strain gradient around it during the rolling deformation process,which significantly promotes the refinement of the structure.The high density of dislocations provides a large number of locations for the nucleation of the precipitated phases,and a large number of nano-precipitated phases are formed in the subsequent low-temperature aging process.The alloy after solid solution has no obvious preferred orientation,and the grain orientation is randomly distributed.After rolling deformation,the extreme density and percentage content of the deformation texture(Brass{110} <112>,Copper{112} <111>,S{123} <634>)increased sharply,and the subsequent low-temperature aging did not significantly change the texture.The type and percentage of structure.High-density nanoprecipitated phases,micro-nano-scale grains and high Taylor-factor texture simultaneously improve the strength and tensile ductility of the rolled sheet.(3)Pre-aging the solid solution alloy to make the alloy have a certain amount of deformable precipitates.The deep cold rolling deformation promotes its re-dissolution,and the re-dissolved solute atoms segregate at the dislocations to form solutes.Clusters of atoms.Warm deformation promotes the diffusion of segregated solute atoms,forming small and dense GP regions in the matrix,which can be directly transformed into the θ’phase during subsequent aging.Pre-aging and temperature deformation control the precipitation behavior in the initial stage of subsequent aging,so that the sample can obtain a relatively uniform distribution of precipitates in the subgrain/inside the matrix during the subsequent aging process.The fine and dense precipitates can effectively inhibit the sub-grain boundary.Migration is conducive to obtaining more fine sub-grains.The improved thermomechanical treatment process can effectively improve the mechanical properties of the alloy,and the hardness of the warm-deformed sample after aging is higher than that of the solid solution-cold-rolledaged sample.Compared with the traditional T6 alloy,the yield strength of the alloy after warm deformation and aging is increased by 71%,and the tensile ductility is similar.