Corrosion rate of AA 7050 in 3.5% NaCl environment with sodium chromate (Na₂CrO₄) inhibitor variation

Universitas Gadjah Mada, Department of Mechanical and Industrial Engineering, Faculty of Engineering, Yogyakarta, Indonesia

^* Corresponding author: ilman_noer@ugm.ac.id

Abstract

Aluminium alloy 7050 is widely used for aerospace applications due to its excellent mechanical properties. However, when the airplane is operated and exposed by the corrosive environment, alumina layer of aluminium is not thick enough to provide protection. Therefore, corrosion protection method in the airplane needs to be improved. In the recent experiments, corrosion process in the airplane could be inhibited by corrosion inhibitors that are mixed with a protective coating. In this current study, the effect of sodium chromate inhibitor on the corrosion rate of aluminium alloy AA 7050 has been investigated. The 7050 aluminium alloys in this experiment were machined into specimens for the tensile test, hardness test, corrosion test and metallographic examination. The corrosion test was performed in 3.5% NaCl solution containing 0.1%, 0.3%, 0.5%, 0.7% sodium chromate inhibitor and the results have been compared with the corrosion rate in 3.5% NaCl solution as reference. The tensile test results showed that the ultimate and yield strength were 527.36 MPa and 481.42 MPa. Hardness test results were 175.36 VHN on the short transverse plane, 164.43 VHN on the long transverse plane, and 164.23 VHN on the longitudinal plane. This experimental study can be concluded that the corrosion rate of material decreases with increasing of Na₂CrO₄ concentration in the solution.