| Microstructure fabrication plays an important role in improving surface properties.Through preparing specific microstructure on the surface,special functions are obtained by material.Meanwhile,material properties can be enhanced.Thus,it shows great application prospect in engineering,which attracts many people's attentions.However,up to now,most of reported microstructure fabrication methods still face some limitations,such as low efficiency,poor reproducibility,unable to process large area,complex operation,polluting environment and so on.More importantly,the adhesion strength between substrate and microstructure prepared by above methods is very low.Moreover,the mechanical strength of the microstructures is very week.Therefore,it is difficult for these microstructure surfaces to be applied in practice.Aiming to above issues,the dissertation selects 7075 Al alloy as research object.Laser marking is investigated.Controllable fabricating microstructure is realized by laser marking.Then,the properties of Al alloy surfaces with specific microstructure prepared by laser marking are investigated thoroughly.Some achievements are obtained.Texture structures can be prepared on Al alloy surface by laser marking.The interreaction between laser and Al alloy surface is investigated.Thermal effect model of material surface affected by laser is built.The variations of morphology,geometrical dimensions,and chemical composition of microstructure on Al alloy surface with laser marking parameters are investigated.The interrelation between laser marking parameters and morphology,geometrical dimensions of microstructure on Al alloy surface is established.The results indicate that melting zone area,overlapping degree of melting zones and sputtering degree of melted material can be changed by laser frequency and laser scanning speed,which has a great effect on morphology and geometrical dimensions of microstructure on Al alloy surface.According to the wettability theory,the wettability model of regular micro-orifice surface is built.Then similar regular micro-orifice array is prepared on Al alloy surface by laser marking.The wettability,superhydrophobicity,self-cleaning property,corrosion resistance,anti-icing property and superhydrophobicity afterfriction of the fabricated microstructure surface are studied.The results demonstrate that the contact angle has an increase with the decrease of distance of each microorifice.As the decrease of diameter of micro-orifice,contact angle of the surface reduces.Therefore,when the distance of each micro-orifice is small(60?m),the fabricated regular micro-orifice array surface shows great superhydrophobicity.The static contact angle is 156°(conatact angle of bare surface is 82.4°).The sliding angle is 3.9°.The contacting area between liquid and material of the superhydrophobic surface is less than 8%,which highly improves self-cleaning property,corrosion resistance,and anti-icing property of Al alloy.The superhydrophobicity of the surface is mainly affected by the integrity of micro-orifice and the low surface energy film on micro-orifice.The protrusion microstructure on the surface can improve superhydrophobicity of surface.Moreover,due to the protrusion microstructure,the surface still has good superhydrophobicity after friction.Lined grooves,gridding grooves,circle grooves,regular orifices array are fabricated on 7075 Al alloy surfaces.The tribological properties of the fabricated surfaces with different textures spacing are studied under different sliding speed.The friction and wear resistance of the surfaces are exposed.Meanwhile,the antifriction and antiwear mechanisms are understood.The results indicate that,if the roughness structure on the surface is not worn out,the roughness structure is able to improve tribological properties of Al alloy greatly.When the sliding speed is low(100mm/s),due to the same orientation of friction and depression structure,the ploughing effect on the surface is highly reduced.Thus,the circle grooves surface of Al alloy(textures spacing of 150?m)shows great tribological properties(61% of friction coefficient of bare surface,30% of wear volume of bare surface).Under high sliding speed(400mm/s),the three-body abrasive wear is reduced by the microstructure that can remove wear debris,significantly.Therefore,the lined grooves surface improve friction and wear resistance of Al alloy greatly.The friction coefficient and wear volume of the surface are about 54% and 32% of bare surface,respectively.According to above research,friction and wear models of microstructure surface are established.The effect of removing/trapping wear debris ability of microstructure,friction direction,distribution density of microstructure and sliding speed on surface tribological properties is discussed.The results show that the friction and wearresistance of microstructure surface are great when the orientation of friction and depression structure on the surface is same.The capability of removing wear debris on the surface of microstructure that can remove wear debris is better than that of microstructure that can trap wear debris.Additionally,the capability of removing wear debris on the surface of microstructure that can remove wear debris is enhanced by sliding speed,which further improves tribological properties of the surface.Moreover,with increase of distribution density of convex structure on the surface,the contact area between surface and frictional pair increases.Meanwhile,the removing wear debris capability of microstructure is diminished.Therefore,as the distribution density of convex structure on the surface increases,tribological properties of the surface are weakened gradually.The established model can be used to guide in the design of microstructure with great antifriction and antiwear performance in engineering application. |
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