Effect Of Laser Biomimetic CeO₂-SiC-Ni Unit On Wear Resistance Of 7075 Aluminum Alloy

In recent years,with energy conservation and emission reduction as a necessary prerequisite for social development and technological progress,industrial materials have gradually transformed to lightweight.Aluminum alloy has become one of the key materials for industrial parts due to its light weight and high specific strength.As a light/soft alloy 7075 aluminum alloy,its wear failure problem greatly restricts the service stability of shaft/rod parts.The effective method to prolong the service life is surface strengthening.However,surface strengthening often sacrifices the inherent properties of aluminum alloys,at the expense of the toughness advantage of 7075aluminum alloy,it brings certain hidden safety hazards for 7075 aluminum alloy of shaft/rod under the stress condition with small soft coefficient of stress state.The effect of alloy strength and toughness cannot be ignored.Therefore,while improving the wear resistance of aluminum alloys,the synergistic deployment of its strength and toughness has become an important research link to improve the safe,efficient and economical application of lightweight aluminum alloys.Taking the biological body with special functions as the biomimetic prototype,the abstracted structural form was processed on the surface of the workpiece,so that the substrate can obtain a structure similar to the function of the biological body while retaining the original excellent performance.By observing the surface of the organism with both high wear resistance and high fracture resistance,the non-smooth characteristics of the"soft-hard"phase provide an important basis for it to withstand external forces and slow stress release.Further exploration found that,the excellent function of biology is not the function of a single characteristic quantity,but the result of the comprehensive influence of multiple characteristic quantities.Inspired by the above,in this study,through the ingenious combination of efficient and controllable laser processing technology and bionics,the laser biomimetic processing method was used to prepare the Ce O₂-Si C-Ni reinforced structure（hard unit）with spaced distribution on the surface of the 7075 aluminum alloy substrate,and formed a biomimetic surface with a soft and hard structure with the matrix,the sample prepared by this method was a biomimetic sample.Through the wear test and tensile test,the synergistic effect of the microstructure and morphological characteristics of the hard unit on the wear performance and fracture toughness of 7075 aluminum alloy was deeply explored,in order to improve the wear resistance of the surface while retaining the excellent fracture toughness performance of the matrix.The results showed that:（1）Microstructure characteristic quantity of unit:the addition of an appropriate amount of Ce element had a positive effect on the wear resistance of 7075 aluminum alloy,with the increased of rare earth content,it showed the law of first increase and then decrease.When the content exceeded 3%,the surface roughness,hardness and wear resistance of the unit all showed a downward trend.Among them,the biomimetic sample prepared with 3%Ce O₂-15%Si C-82%Ni mixed powder had the best anti-wear performance.（2）The characteristic quantity of the unit morphology:As a strengthening area,the shape regulation of the unit played a directional guiding and blocking effect on unidirectional stress wear and tensile fracture,and also affected the wear resistance and fracture toughness of the biomimetic surface-strengthened samples.Among them,the reticulate unit was composed of bidirectional strip-shaped units,and the whole can be regarded as two parts:an approximate strip-shaped hard area（strip-like area）and an approximate point-shaped hard area（node area）,which had both the multi-directional dredging effect of the point-shaped unit and the damage blocking effect of the strip-shaped unit.In addition,with the changed of unit spacing,its organization also changed,among which the reticulation unit with 2.5mm spacing had the most dense and uniform organization,the elongation at break of the biomimetic sample in which it is located was the closest to that of the untreated sample,showing high tensile strength and wear resistance.（3）The microscopic mechanism of the wear and fracture process of the biomimetic sample:the optimization of the fracture toughness of the aluminum alloy by the reticulate unit mainly depended on the uniform and refined structure of the processing area,which hindered the initiation and propagation of cracks during the stress process of the sample,and the combined action of the strip-like area and the node area in the unit make the stress relieved.In addition,due to the formation of hard phases such as Al₃Ni₂ and Al₄C₃,the biomimetic samples also played a role in dispersion strengthening.（4）Coordinated mechanism of wear and fracture of biomimetic surfaces:The increased in yield strength caused by the small and uniform dense structure can effectively resist the effect of loading force on the sample;While the unit played the role of concentrating stress to protect the substrate,the multi-directional dredging function of the point-like area can guide the force to be evenly distributed on the surface of the sample;The strip-like area unit acted as an obstacle to the movement of wear debris,grinding,and retardation of crack propagation during the stretching process;While the hard unit was under stress,part of the force was transmitted to the matrix,and the soft aluminum alloy took advantage of its strong deformability and absorbed part of the stress.