| The 7075 aluminum alloy as an aerospace structural material has its own surface performance defects,such as poor corrosion resistance and relatively under-performing hardness,which severely limit the requirements for its continuous development.It can improve its comprehensive performance through micro-arc oxidation techniques to expand its application range.In constant current mode,keep the base electrolyte(12 g/L Na2SiO3,2 g/L Na OH,1 g/L EDTA-2Na)unchanged,use control single variable method,exploring the influence of forward current,pulse frequency and duty cycle to micro-alignment film layers,and determine the optimal parameter combination.Different concentrations of nano-TiO2 additives were added to the base electrolyte under this electrical parameter combination,exploring its concentration changes on the morphology and performance of the film layer,and determine the optimal nano-TiO2to add concentrations.The results show:When the forward current is 3?9 A,as the forward current is increasing,the thickness of the membrane gradually increases,the film layer has increased from 8.2?m to 22.4?m,an increase of 14.2?m;the Al2O3 phase in the membrane layer increases,the surface of the membrane layer surface is constantly increasing and the holes are constantly decreasing;the hardness is reduced and decreases,the hardness value increased from 255.9 HV to 354 HV,an increase of98.1 HV;after the film layer corrosion resistance is increased and then weakened,the corrosive current density was reduced from 1.284?A·cm-2 to 0.402?A·cm-2,and0.882?A·cm-2 was reduced.When the pulse frequency is 200?1000 Hz,as the pulse frequency is increasing,the thickness of the film is gradually reduced,the thickness of the membrane layer was reduced from 28.7?m to 14.3?m,a decrease of 14.4?m;the Al2O3 phase changes little,the surface of the membrane layer has increased and then increased,and the hole is less,the distribution is even more uniform;the hardness increases first and then decreases,the hardness of membrane layer has increased from 274.2 HV to 354 HV,an increase of 79.8 HV;the frequency on the micro-alignment film is small,the corrosion potential and corrosion current density at each frequency are small,the corrosion current density is reduced from 0.533?A·cm-2 to0.402?A·cm-2,and it reduces 0.131?A·cm-2.When the duty cycle is 10?50%,as duty cycle is increasing,the thickness of the film is increased from 11.2?m to 20.8?m,an increase of 9.6?m;the Al2O3phase changes little,the surface of the membrane layer is first reduced and the aperture is reduced and increased;the hardness increases first and then decreases,the film hardness increases from 317 HV to 354 HV,an increase of 37 HV;after the film layer corrosion resistance is increased and then weakened,the corrosion current density is reduced from 1.237?A·cm-2 to 0.402?A·cm-2,and it reduces 0.835?A·cm-2.When the forward current is 6 A,the pulse frequency is 600 Hz,and the duty cycle is 30%,the film layer has a thickness of 18.4?m,the surface of the membrane layer is relatively flat,the melt stack is less,the hardness is 354 HV,the film layer is from the corrosion potential of-0.7480 V,the self-corrosion current density is 0.402?A·cm-2,corrosion resistance the best.After adding nano-TiO2 additives,the membrane layer has improved a certain degree of improvement in terms of thickness,surface quality,hardness and corrosion resistance.With the concentration of nano-TiO2 additive concentration,Micro-arc oxide film layer thickness is increasing;the surface of the membrane surface is constantly decreasing,the melt stack is increasing,and the density is improved;the object group of the micro-arc oxide film is Al,?-Al2O3,?-Al2O3and a small amount of nano-TiO2 particles,nano-TiO2 particles are embedded in the micro-arc oxide film layer;the hardness of the micro-arc oxide film is increasing;membrane corrosion resistance is constantly enhanced.When the nano-TiO2 concentration is 4 g/L,the film layer is 23.9?m,and the Al2O3 is more,the hardness reaches the maximum value of 384 HV,the corrosion resistance is preferably-0.5323 V,self-corrosive current density 0.013?A·cm-2,the film layer is best in good performance. |
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