SURFACE-ANALYSIS OF AIR EXPOSED RAPIDLY SOLIDIFIED ALUMINUM POWDER

Rapidly solidified powders of pure aluminium and aluminium alloy A15Mn 2.5Cr were produced by the ultrasonic gas atomisation method. After ex posure to a humid atmosphere the powders were analysed using ESCA and Auger spectroscopy. The powders were exposed at room temperature to a humid atmosphere for 1 h, 1 day and 1 week. The relative humidities (R H) were 60% and 80%. During exposure to conditions of 60% RH for 1 day or 80%RH for 1 h, a thin layer of hydroxide formed on the powder surf aces. Exposure for longer times causes formation on the surface of thi cker Al(OH)3 particles which were formed by hydration of the oxide and corrosion of the aluminium metal. The amount of Al(OH)3 formed increa ses with exposure time and relative humidity. Manganese and chromium i n the A15Mn2.5Cr alloy have an inhibiting effect on the corrosion proc ess, probably due to stabilisation of the surface oxide.