Study On Appearance And Residual Stress Of Cold Spray Al-7075 Coating On Mg-alloy Surface

Cold spraying technology(CS)is a new spraying process which uses compressed gas(nitrogen,helium,etc.)as an accelerating medium to drive solid metal particles to impact the substrate at extremely high speed,causing strong plastic deformation of particles and depositing them to form coatings.However,when the particles collide with the substrate at high speed,it will lead to the generation of residual stress,which is one of the important factors affecting the quality of the coating.This paper,AZ31B magnesium alloy,a commonly used material for aircraft wing skins,and A1-7075-T6 powder particles,a coating material,selected for the study.The effects of different process parameters on the morphology of the deposited coatings and the residual stress patterns are analyzed by a combination of theoretical analysis,finite element simulation and orthogonal tests,and the obtain optimal process parameters are applied to the preparing of actual coatings to prove the feasibility of the model.The specific research works in this paper are as follows:(1)By studying the bonding mechanism of cold spraying and the basic theory of explicit dynamics of particle collision,the factors leading to the generation of residual stresses during the coating preparation process were analyzed,and the appropriate numerical theory,corresponding material constitutive relationships,element types and contact models were determined.(2)Using the CEL algorithm in ABAQUS to establish a single particle collision model.The impact process of cold sprayed single particles was investigated.The influence of various process factors on the coating morphology and residual stress variations during the deposition process is demonstrated by the plastic strain and residual stress variations in particle collisions.In combination with the orthogonal test,rational spraying process parameters were identified and the significance of the model was confirmed.(3)According to the method parameters obtained from the orthogonal test and the single particle crash model,modeling multi-particle collisions.The transformation of the coating morphology during the deposition of adjacent three-particle,vertical three-particle and multilayer staggered stacking was investigated,and the variation of residual stresses under each of these three conditions was concluded.(4)Using BSX-800LP high pressure cold spray equipment for coating preparation.Comparison of the actual coating morphology and process parameters with the numerical simulation of the deposition morphology and the preferred combination of process parameters from the response surface analysis to further optimize the simulation model.By comparison,the microscopic morphology of the actual coating matches the results of the finite element simulation,thus verifying the reliability of the simulation results.