Thermophysical and electrical properties of chromate conversion coatings on Alclad AA7075-T6 Aluminum alloy

Thermophysical properties, electrical contact resistance (ECR) and corrosion performance are considered as critical properties of coatings, which are utilized in the satellite manufacturing industry. Chromate conversion coatings (CCCs) for Al alloys are among these coatings.In this study, CCCs were applied on Alclad AA7075-T6 Al Alloy by means of a chromating solution having chemical composition very near to the commercial chromating solution of Alodine 1200S. Influence of coating time on the coatings thermophysical properties including coefficients of solar absorption or Absorptivity (αs) and thermal emission or Emissivity (εT) as well as their ECR values were investigated. The εT was measured directly by Emmisometer device, while αs was determined indirectly by Reflectometer equipment. In coating time from 30 up to 180 seconds αs and εT values were measured in the ranges of 0.7-0.94 and 0.06-0.22, respectively. The results were revealed that different εT and αs as well as desired ECR values according to the specifications of satellite industry are obtainable by control of coating parameters such as coating time. In addition, base on the results of surface coating morphology evaluating conducted by SEM and AFM, it was concluded that developed coatings were formed in nanocrystalized structures.