The Accelerated Atmospheric Corrosion Testing of Al Casting Alloy and its Monitoring Method

Abstract

　Al-Si-Cu alloys are often used in combination with bolts made of high-strength, Ni-alloy for joining casing components together. When seawater or rainwater intrudes a joint area between an Al-alloy casing and a Ni-alloy bolt, for example, the problem of galvanic corrosion may occur in and around the joint area. Then, this study focused on the galvanic corrosion of Al/Ni galvanic pair under dry/wet cycles. To simulate the wetting/drying process of the brine, the metal pair was put on a heater, which was kept at either 150℃ for 15 min or 80℃ for 45 min. To estimate the corrosion rate in the test environment, the Al-Ni (C355.0/Alloy 718) pair was connected to a zero-resistance ammeter to measure the corrosion current between the metals. The corrosion rate of the galvanic couple of Al and Ni alloys depends on the reduction reaction of H₂O in the surface water film. We have obtained the following findings as regards the corrosion acceleration test on the Al-Ni (C355.0/Alloy 718) galvanic couple and the monitoring method in the test. The amount of corrosion depends on the wetness duration, and corrosion is accelerated by maintaining the wet environment.