Influence of Contaminated NH3 on Stress Corrosion Behavior of 7075 High Strength Aluminum Alloy in Marine Atmosphere Environment

Abstract

The addition of NH 4 + in NaCl which could simulate the marine atmosphere environment contaminated NH 3 accelerates the corrosion process of 7075 high strength aluminum alloys. The acceleration effect is mainly promoted by the reaction process of aluminum alloy cathode. This is due to the fact that NH 4 + leads to the acidification of solution to promote the occurrence of cathodic reaction. The addition of NH 4 + increases the stress corrosion susceptibility of the 7075, and the sensitivity of stress corrosion increases with the increase of NH 4 + concentration. The reason is that the acceleration of the cathodic reaction process caused by NH 4 + promotes the precipitation of hydrogen and the diffusion in the aluminum alloy. At the same time, the corrosion effect of the aluminum alloy also changes the mechanical properties of the aluminum alloy, and the stress corrosion sensitivity of the high strength aluminum alloy increase. 1． Introduction7075 high-strength aluminum alloy has been widely used in the aviation industry due to the high strength and low density. However, in the marine atmospheric environment, high-strength aluminum alloy prone to pitting, intergranular corrosion and peel corrosion, or even stress corrosion cracking. It is a serious threat to the safety of equipment services made of 7075.At present on the corrosion of aluminum alloy in the natural environment has been carried out a certain study [1][2][3][4][5][6][7]. Researchers found traces of pitting [1][2][3][4][5], intergranular corrosion [3,6,7], peel corrosion [6,7] and stress corrosion cracking [3]. Sun et al. [6] studied the corrosion behavior of 7075 aluminum alloys in rural, marine and industrial environments atmosphere, and found that the aluminum alloy was significantly eroded with peel corrosion and resulted in a significant decrease in mechanical properties. Based on the literature resources, we found that the study of stress corrosion of high strength aluminum alloys in the atmosphere is still small. We believe that this is because the natural environment corrosion test generally needs a long time, but the completed test is mainly concerned with the weight loss and morphology change for the corrosion. It is difficult to carry out in-depth study of its stress corrosion behavior.Recently, researchers usually use the tensile test in the solution for the study of stress corrosion of aluminum alloy [8][9][10]. But in the marine atmosphere, the essence of aluminum alloy corrosion is the electricity chemical process in unsteady thin electrolytes layer whose thickness, shape and distribution will be of cyclical changes due to temperature, humidity, light, rainfall and other factors with alternating effects. The unsteady characteristics of the thin film are mainly manifested in the dynamic and dispersive, dynamic can lead to thin film thickness from several molecular layer to several millimeters change, and the dispersion leads to material, liquid film and gas composition Of the "gas / liquid / solid" three-phase interface area i...