Corrosion Behaviour of Aluminum Alloy AA7075-T651

The present work investigates the corrosion behavior of a high strength aluminum alloy AA7075-T651 which is widely used in the aerospace industry. The alloy composed of Zn, Mg, and Cu as the main alloying elements. The T651 referred to a peak strength temper. X-ray diffraction (XRD) analysis detected MgZn₂ as the second phase next to the Al matrix. The corrosion behavior of AA7075 was studied by conducting an immersion test in 30 g/l NaCl and 10 ml/l HCl solution at 35°C based on ASTM B597 for 8, 16, 24 h. The specimen was then characterized by an optical microscope and scanning electron microscope (SEM). The results showed that the specimen experienced a severe corrosion attack as a result of immersion test, as indicated by the change in the surface appearance, the development of surface roughness, as well as significant weight loss. The surface became remarkably rough and grain embrittlement following the metal grain boundaries occurred down to 150 μm depth. The near surface layer became disintegrate and easily detached from the surface after immersion 16 and 24 h. The results indicated that the alloy was sensitive to intergranular corrosion.