Research On Microstructure Evolution And Strengthening-toughening Mechanism Of Al-Mg-Si Alloy Under Electric-thermal-strain Coupling Field

Aluminum alloy accounted for an increasing proportion in aerospace,rail transit and automotive fields because of its excellent electrical conductivity,thermal conductivity,excellent strength and plasticity,good weldability,workability and corrosion resistance and other advantages.With the continuous development of industrial technology,the requirements of shorter process,higher efficiency and better mechanical properties have been put forward for the processing and preparation of aluminum alloy.Although the traditional heat treatment process has a mature process system,it can also improve the mechanical properties of aluminum alloy,but there are problems such as long process cycle and severe test in production efficiency.As for the material,its performance mainly depends on the structure of the structure,aluminum alloy is very sensitive to temperature,in the control of temperature stability,the traditional technology has many difficulties.Based on the two main strengthening mechanisms of aluminum alloy,such as grain boundary strengthening and precipitation strengthening,thermal-mechanical treatment can be used as a mature and effective strengthening method.However,due to the high fault energy of aluminum alloy,the heat treatment parameters of the material are too strict.Some new methods of preparing ultrafine grain can not meet the requirements of comprehensive mechanical properties of aluminum alloys,because when the ultrafine grain are obtained,the ductility will decline.Therefore,a new and efficient method to improve the mechanical properties of aluminum alloy will be an inevitable choice for the development of aluminum alloy industry.Electropulsing technology is a technology that can significantly change the microstructure and mechanical properties of materials by inputting high-energy electro-thermal-strain coupling field into materials in a short period of time.At present,the technology has been widely used in liquid metal solidification,fatigue crack repair,microstructure refinement and other fields.In addition,some achievements have been made in simultaneously improving the strength and toughness of metal materials via electropulsing treatment.Therefore,using electropulsing technology for the treatment of aluminum alloy,to meet the needs of aluminum industrial production,to achieve the goal of efficient,high mechanical properties has important theoretical and guiding significance.In this paper,Al-Mg-Si alloy?6061 aluminium alloy?was used as the experimental material to successfully prepare superior strength and superior toughness 6061 aluminium alloy by adjusting pulse current processing voltage,duration and action time of pulse current.By means of a variety of microstructure characterization methods and mechanical properties detection methods,the microstructure evolution and toughening mechanism of the alloy under different electropulsing treatment methods were revealed from the perspectives of morphology observation,finite element simulation and calculation.The conclusions are as follows:?1?The influence of electric-thermal-strain coupling field on the precipitation process of6061 aluminium alloy was revealed.The precipitation behavior of 6061 aluminium alloy changes as follows,depending on the voltage,duration and timing of pulse current processing:The high voltage and short time electropulsing treatment on the solid solution state of 6061 aluminium alloy can promote the precipitation of Al₅FeSi phase and effectively pin the dislocation;the low voltage and high time electropulsing treatment of the solid solution state 6061 aluminium alloy promoted the precipitation of Mg₂?Si,Cu?₃clusters,effectively delayed the yield stage in the plastic deformation process and prevented the entanglement of dislocations;electropulsing treatment of rolled 6061 aluminium alloy promoted the precipitation of Mg₄?Si,Cu?cluster,the cluster has a Cu-rich core-shell structure,which can effectively prevent its growth in aging process,and avoid the occurrence of overaging.?2?The influence of pulse current on dislocation motion and configuration is revealed.For the initial state with low dislocation density,when the angle between the current direction and the dislocation direction changes from 0^o to 90^o,the pulse current can promote the slip and increment of the dislocation,and promote the formation of cell-shape configuration with isotropy,which can make the Mg₂Si phase in the aging process become spherical;as for the initial state with high dislocation density,the pulse current can effectively break the configuration of dislocation entanglement,promote the formation of dislocation network structure with regular arrangement and higher stability,provide more nucleation locations for the precipitation of Mg₂Si phase in aging process,and also make the alloy with subsequent aging state have higher dislocation density.?3?It was revealed that the electropulsing treatment greatly promoted the recrystallization process of solid solution+cold-rolled samples and refined the?-Al grain.At the same time,the electron wind strongly impinges on the?-Al grain boundary and produces a large number of crystal defects,so that the?-Al grain boundary is fully infiltrated by the Mg₄?Si,Cu?cluster.In addition,under the action of current and under the influence of the enhanced diffusion flux of Mg element,the size distribution of precipitated phase from inside the grain to the grain boundary changes in a gradient.The precipitation of Mg₄?Si,Cu?clusters and Mg₂Si phase reduced the solute concentration of the matrix,weakened the interaction between dislocation and Cottrell atmosphere,and thus inhibited the PLC effect in the plastic deformation process,making the deformation more uniform and stable.?4?It was revealed that the microstructure refinement of 6061 aluminium alloy was successfully achieved by electropulsing cyclic treatment without any phase transition or plastic deformation.Compared with the traditional cyclic treatment alloys,the grain size of the electropulsing cyclic treatment alloys was refined by 96.6%.In addition,electropulsing cyclic treatments also significantly accelerated the dislocation motion on the denser packing plane?111?and promoted the formation of corresponding low angle sub-grain,which increased the textured strength of{111}//ED.The appearance of this texture can avoid the cleavage crack transgranular propagation and is beneficial to the strength and toughness of the alloy.?5?The strengthening and toughening mechanism of 6061 aluminium alloy under pulsed current is revealed.Compared with traditional treatment,electropulsing treatment can improve the contribution of dislocation strengthening and precipitation strengthening to yield strength of aging alloy.For cold rolled alloys,electropulsing treatment can increase the contribution of grain boundary reinforcement to yield strength.In addition,the plasticity of 6061 aluminium alloys was improved under the combined effects of grain refinement,cellular configuration of necessary geometric dislocations,and favorable crystal orientation.?6?It is revealed that the strength and plasticity of 6061 aluminium alloy can be improved in a very short time by electropulsing treatment,which breaks the trade off of strength and ductility in the traditional treatment process,and the 6061 aluminium alloy with superior strength and superior toughness is successfully prepared,which greatly improves the processing efficiency.Compared with the traditional T6 state 6061 aluminium alloy,the tensile strength of the superior strength 6061 aluminium alloy treated by pulse current increased by 47.2%and the comprehensive mechanical properties increased by45.4%.Compared with the traditional solid solution state sample,the tensile strength of the superior toughness 6061 aluminium alloy treated by pulse current increased by 48.9%,and the plasticity increased by 78.9%compared with the traditional 6061 aluminium alloy in T6state.In this paper,by choosing different voltage pulse current processing,pulse current time,duration and reveals the effect of pulse current on the morphology evolution and strength mechanism of aluminum alloy,pulse current can be confirmed to further improve the mechanical properties of Al-Mg-Si alloy,offers experiment reference and theoretical basis to develop a new kind of efficient method to improve the mechanical behavior of aluminum alloy.