Study On The Microstructure And Properties Of Ni/Al Surface Composite Strengthened Layer With High Volume Fraction Prepared Based On FSP

The particle reinforced aluminum matrix surface composite material can improve the strength and wear resistance of the aluminum alloy while retaining the original toughness and ductility of the aluminum alloy matrix,so as to meet the different performance requirements of the surface and internal parts of the components.The field of scientific research has received extensive attention.And it can improve the comprehensive performance of composite materials by increasing the volume fraction and the uniformity of the structure.However,the increase in volume fraction is affected by the adaptability relationship between the reinforcing particles and the matrix.At the same time,due to the presence of a large number of reinforcing particles,the plastic forming processability is deteriorated,and even the component is difficult to form,which greatly limits its Application and development.Therefore,it is of great significance to study the adaptability relationship between reinforced particles and matrix to further increase the volume fraction,and to explore the high strain rate plastic forming research in high volume fraction particle reinforced aluminum matrix composites FSP process,is expected to become an effective way to solve this problem.In this paper,Ni/Al composites were prepared from four typical aluminum substrates through optimized friction stir processing methods to study the adaptability of Ni particles to aluminum alloy substrates.On this basis,2024Al with the best adaptability to Ni particles was selected as the matrix material,Ni/Al surface composites with Ni volume fraction of 7.1vol%-26.8vol%were prepared,and the volume fraction of Ni/Al prepared by FSP was studied.The influence law of microstructure and mechanical properties of surface composite materials,and the establishment of relevant plastic metal migration model.The main research results obtained are as follows:(1)The adaptability of Ni particles to different aluminum alloy systems and the influence of matrix type on the forming quality of composite materials are revealed.The shape of the stirring zone of Ni/1060Al composite is regular and the range is the largest,the particles react fully,and there is almost no agglomeration;Ni/5083Al composite has the smallest stirring zone and the most irregular profile,and the agglomeration phenomenon is also the most serious.When the matrix of the composite material is 2024Al,the Ni particle-reinforced composite material has better bonding strength and uniform organization structure,and shows better adaptability to Ni particles.The Ni/1060Al and Ni/6061Al composite materials have stable microhardness curves in the agitated zone,with small fluctuations.The tensile strength of the composite material is improved compared to the matrix material.The tensile strength of the Ni/6061Al composite material can reach 228MPa,an increase of 82.4%,the most obvious strengthening effect.From the perspective of the strengthening effect of Ni/Al composite materials,Ni/6061Al composite materials have the most prominent strengthening effect among different aluminum alloy systems,and Ni/2024Al composite materials have the best comprehensive performance.(2)The main reinforcement phase Al₃Ni exists in the composite in three main forms,namely:core-shell structure(shell layer),micron particles,and submicron particles,which are reacted and broken during the FSP process through different aggregation forms of Ni particles And dispersed.The forming effect of each area of the mixing area is affected by the direction of the fluid and the quality of the fluid flowing through each area of the mixing area,which in turn affects the final forming of the entire mixing area.In the flow zone,the metal that softens and contacts the shaft shoulder and the stirring pin takes the lead in plastic flow.After the metal flow in the flow zone is completed and stabilized,the flow zone starts to enter the flow state after being pushed by the metal in the flow zone.As the stage progresses,the softened metal radiated by the stirring head(shoulder and stirring pin)gradually enters the plastic flow state,and the volume of the flow area gradually decreases until all the softened metal enters the plastic flow state,forming the final stirring area form.(3)The influence law of Ni volume fraction on the forming characteristics and hardness of FSP composites was clarified.Ni/Al surface composites with Ni volume fractions of 7.1 vol%,14.2 vol%,24.3 vol%and 26.8 vol%were obtained by changing the arrangement and number of powder-filled pore arrays.Macro-forming is relatively good,without obvious defects.As the volume fraction of Ni in the composite material increases,the effect of metal plastic flow in the horizontal direction is significantly greater than that in the vertical direction,the agglomeration phenomenon is more obvious,and the black agglomerates are mostly distributed in horizontal bands.The micro-hardness of the four volume fraction composites are higher than that of the matrix materials,which are increased by 11%,15%,26%and 28%,respectively.When the Ni volume fraction increases to 26.8vol%,the hardness-strengthened zone is band-shaped.(4)When the powder volume fraction of the surface composite material increased from 7.1vol%to 26.8vol%,the tensile strength of the surface composite material increased first and then decreased,respectively 277.9 MPa,289.3 MPa,323.7 MPa and301.5 MPa In comparison,the average tensile strength of surface composites has increased by 45.4%,53.1%,66.3%,and 60.9%,respectively.When the volume fraction of the surface composite material increases from 7.1vol%to 21.3vol%,the tensile strength is more obvious,and the maximum tensile strength is reached when the volume fraction is 21.3vol%.When the volume fraction increases to 26.8 vol%,the tensile strength decreases.While the strength of these surface composites has increased significantly,they still retain considerable ductility and improve surface wear resistance.