THE EFFECT OF ELECTROLYTE TEMPERATURE AND SEALING SOLUTION IN ANODIZING OPERATION ON HARDNESS AND WEAR BEHAVIOR OF 7075-T6 ALUMINUM ALLOY

摘要

Anodic oxide coatings are applied on aluminum alloys in order to improve corrosion resistance and to increase hardness and wear resistance. In the current study, a hard anodic coating was applied on AA7075-T6 aluminum alloy. To survey the anodizing temperature (electrolyte temperature) effect, three temperatures, namely, -5 degrees C, 0 degrees C and 5 degrees C were chosen and the samples were sealed in boiling water and sodium dichromate to study the role of sealing. For measuring the oxide coatings porosity and hardness and also for comparing the samples' wear resistance field-emission scanning electron microscopy (FESEM), microhardness test and pin-on-disk method were utilized, respectively. The results showed that by increasing the anodizing temperature, hardness and consequently wear resistance decreased so that hardness and weight loss in the samples with no sealing decreased from 460 HV and 0.61 mg at -5 degrees C to 405 and 358 HV and 1.05 and 1.12 mg at 0 degrees C and 5 degrees C, respectively, which is due to the porosity increment by increasing the anodizing temperature. Also, sealing in boiling water and dichromate contributed to soft phases and coating hydration, which resulted in a decrease in hardness and wear resistance. Hardness and weight loss in the coated samples at -5 degrees C decreased from 460 HV and 0.61 mg in the samples with no sealing to 435 and 417 HV and 0.72 and 0.83 mg in the samples sealed in boiling water and dichromate, respectively.