Investigation On Shot Peeningn Of Cnt/Al Alloy Composite And Its Characterization

To date,carbon nanotube reinforced aluminum matrix composites have attracted wide,increasing attention in the development of new-generation high-stiffness metallic,highstrength,lightweight materials for electronic and military devices and high-speed transportation.For components used in these fields as structural components,fretting,fatigue,corrosion,wear,and the erosion type of failures usually occur on the surface;therefore,surface integrity remarkably influences product performance.Shot peening is widely exploited to enhance the surface properties,especially the fatigue performance,of components.In the present research,for the first time,the influence of SP on the CNT/AlMg-Si alloy composites was explored.The present research aimed to investigate the surface layer characteristics of a CNT/Al alloy composite after shot peening and explore the stability of the residual stress field during annealing process and cyclic deformation.Mechanical properties of the peened layer were also characterized.Conventional shot peening,stress peening,warming peening and compound peening treatment were carried out to strength the surface layer of the CNT/Al alloy composite.Results shows that the residual stress field of the CNT/Al composite could be further improved via stress peening.Warming peening could generate a more stable residual stress field coMPared with traditional peening treatment.Moreover,compound peening could reduce the surface roughness and improve the residual stress of the surface layer.ANSYS software was employed to simulate the single and multi-SP process.The results showed that residual stress was distributed inhomogeneously between Al base metal and carbon nanotube.Residual stress became discontinuous between different phases.Base metal showed the compressive residual stress(CRS)but the second phase possessed the opposite.Magnitude and depth of CRS were increased with the increasing shot velocity and/or coverageMacro and micro residual stresses in the shot-peened layers decreased firstly due to thermal recovery and then trend to be stable with annealing time at elevated temperatures(150,200,250 °C).Increasing the annealing temperature could accelerate the speed of stress release and increase the decrement rate.Specially,the addition of CNTs could improve the thermal stability of the macro residual stress created by shot peening.alloy induced by traditional SP treatment could be improved byAfter shot peening,the maximum average microhardness under different SP intensities was at the upper surface.The value of average microhardness gradually decreased along the increasing depth.Meanwhile,as the SP intensity increased,the depth of the hardened layer increased.The surface mechanical properties of shot-peened CNT/Al alloy composites were measured via a specific in-situ X-ray stress analyzer combined with a uniaxial tensile tester.The Young's modulus and yield strength of the surface layer with and without peening treatment were calculated using the Von Mises stress criterion.Moreover,residual stress relaxation behavior under cyclic loading was investigated.Results showed that peening treatment can improve the yield strength of the surface layer significantly and only slightly affect the Young's modulus.Meanwhile,stress relaxation behavior in this work depended on the initial residual stresses,amplitude of applied load,and the number of cycles.