Study On Interface Behavior Of AZ31BMg/6061Al Composite Based On Nanoindentation Method

Magnesium alloy is currently one of the most widely used lightweight alloys,which is used in various fields such as aviation and aerospace due to its characteristics.However,the shortcomings of magnesium alloys at room temperature need to be solved urgently,such as poor machinability and poor corrosion resistance.Aluminum alloy is a light alloy second only to Mg alloys,and has good plastic deformation ability and corrosion resistance.Therefore,Mg/Al composites can better meet actual needs by combining the advantages of the two,and it has important application value to achieve a stable connection between the interface of the two materials.As one of the effective methods for studying the microscopic properties of materials,the nanoindentation method has been widely used to test the mechanical properties of thin films,biological materials and heterogeneous structures.This paper proposes to quantitatively characterize the elastoplastic deformation of Mg/Al alloys composite tubes based on the nanoindentation method,and analyze the mechanical properties of the material.In this paper,indentation tests were performed by the nanoindenter with different maximum loading loads(20 m N,30 m N,40 m N and 50 m N)on Mg alloy tubes and both sides of Mg/Al alloy composite tubes to obtain displacement curves,hardness and elastic modulus.The indentation deformation behavior of Mg alloy tubes was analyzed based on the nanoindentation method.The load-displacement curves obtained by the indentation were converted into stress-strain curves by the dimensional method and the basic principle of nanoindentation,and the elastoplastic parameters such as the work hardening index and yield strength of the material were calculated.The microstructure evolution and nanomechanical properties on both sides of the interface of composite tubes under different reductions were analyzed,and the influence of the structure on the properties were studied.In addition,the ABAQUS software was used to simulate the nanoindentation process of the Mg/Al composite tubes,and acquired the load-displacement curves and the distributions of stress and strain field.Finally,the residual indentation morphology and pile-up obtained by simulation and experiment were analyzed,and the influence of different indenters on the size of plastic zone,the height of pile-up and the direction of flow deformation were further explored.For Mg alloy tube,the influence of different deformation amount on the mechanical properties was analyzed based on the nanoindentation method.The grains of AZ31BMg tubes were obviously refined after different spinning passes.The load-displacement curves show that the plastic deformation caused by spinning directly affects its indentation deformation.According to the nanoindentation experiments,the depth,indentation work recovery rate,yield strength and hardening index were analyzed.Additionally,the calculated yield strength and hardening exponent of the cylinders were in the range of 42.0±0.5?125.5±0.6 MPa and0.182?0.017 respectively with the increase of spinning passes.Nanomechanical properties and microstructure of Mg/Al composite tubes at different thickness reductions were discussed based on the analysis of the indentation behavior for magnesium alloy tubes.With the increase of thickness reductions,the average grain size of composite tubes on both sides of Mg and Al decreased from 14.19 to 3.11?m,and from 8.61to 2.08?m.In addition,the geometrically necessary dislocation density on the Mg alloy side increased from 0.25×10¹⁷ to 1.10×10¹⁷ m^-2,while the aluminum alloy side increased from4.1×10¹⁶ to 9.3×10¹⁶m^-2.Correspondingly,the hardness on both sides of the interface gradually increases,and the difference between the yield strength and the hardening index on both sides of Mg and Al alloys gradually decreases,and the dislocation density increases with the increase of the thickness reductions.The load-displacement curves obtained from simulation were analyzed,and the feasibility of the model was verified.According to the results of simulation,as the thickness reduction increases,the maximum indentation depth and peak stress after unloading on both sides of Mg and Al alloy gradually increased,and the maximum plastic strain PE_max after completely unloading decreased by 7.9%and 17%,respectively.In addition,Berkoviech and conical indenters have little influence on the load-displacement curves and stress field,but have a greater influence on PE_max and the relative errors are 25.3%and 31.8%,respectively.The residual indentation morphologies obtained by simulation and nanoindentation experiment were compared and analyzed,indicating the pile-up of indentation morphology both sides of Mg and Al alloy.With the increase of the thickness reduction,the height h_r of pile-up on both sides of Mg and Al decreased by 10.7%and 16.2%,respectively.According to the size of Mg and Al sides obtained under different indenters,it was proved that the indenter has almost no influence on the size of the indentation,but it had a greater influence on the height of pile-up and the relative errors are respectively 3.3%and 10.4%.The study of the nanomechanical properties of Mg/Al composite tubes based on nanoindentation method will provide a reference for the theoretical methods to quickly and accurately obtain the mechanical properties in micro-zone of materials.