Table 4-2.—Corrosion of Metals—Nature and Appearance of Corrosion Products ALLOY TYPE OF ATTACK TO WHICH APPEARANCE OF ALLOY IS SUSCEPTIBLE CORROSION PRODUCT Aluminum Alloy Surface pitting, intergranular, White to gray powder. exfoliation, stress corrosion, fatigue cracking and fretting. Titanium Alloy Highly corrosion resistant. Extended   No visible corrosion products at low or repeated contact with chlorinated temperature. Colored surface oxides solvents may result in degradation develop above 700°F. of the metal's structural properties. Magnesium Alloy Highly susceptible to pitting. White powder snowlike mounds and white spots on the surface. Carbon and Low-Alloy Steel Surface oxidation and pitting, Reddish-brown oxide (Rust). surface and intergranular. Stainless Steel Crevice/concentration cell Rough surface; sometimes a red, (300-400 series) corrosion; some pitting in marine brown, or black stain. environments; corrosion cracking; intergranular corrosion (300 series) and surface corrosion (400 series). Nickel-base Alloy Generally has good Green powdery deposit. (Inconel, Monel) corrosion-resistant qualities; susceptible to pitting in seawater. Copper-base Alloy Surface and intergranular corrosion. Blue or blue-green powdery deposit. Brass, Bronze Cadmium (protective plating for Good corrosion resistance. Will White powdery deposit to steel) cause embrittlement if not properly brown/black mottling of the surface. applied. Chromium (wear-resistant plating Subject to pitting in chloride Chromium being cathodic to steel, for steel) environments. does not corrode itself, but promotes rusting of steel where pits occur in the coating. Silver Will tarnish in presence of sulfur. Brown to black film. Gold Highly corrosion resistant. Deposits cause darkening of reflective surfaces. Tin Subject to whisker growth. Whiskerlike deposits. nature and appearance of corrosion products found on the metals used in aircraft construction. Iron and Steel Possibly the best known and the most easily recognized form of metals corrosion is the familiar reddish-colored iron rust. When iron and its alloys corrode, dark iron oxide coatings usually form first. These coatings, such as heat scale on steel sheet stock, may protect iron surfaces. However, if enough oxygen and moisture are present, the iron oxide is soon converted to hydrated ferric oxide, commonly known as iron rust. Iron and steel are used in avionic equipment as component leads, magnetic shields, transformer cores, racks, and general hardware. Steel and iron hardware used in aircraft construction is usually plated with nickel, tin, or cadmium. Aluminum Aluminum and its alloys are used many places in aircraft construction, including ejection seats, chassis 4-35