334 Section 4 Nonferrous Metallurgy –1.6 –1.4 –1.2 –1.0 –0.8 –0.6 –0.4 –0.2 0.0 0.2 Zinc Aluminum alloys Carbon steel & cast iron Yellow brass (UNS C23000) Tin Copper Stainless steel (UNS S41000) Copper-nickel (UNS C70600) Lead Silver Stainless (UNS S31600) Inconel 825 (UNS N08825) Titanium Gold, platinum Graphite More noble—cathodic Less noble—anodic Magnesium Goodheart-Willcox Publisher Figure 15-13. The electronegativity of select metal alloys is shown here relative to a standard hydrogen electrode. For any pair of metals in electrical contact, the more electronegative (less noble) metal will corrode more than it would by itself. The less negative (more noble) metal in a pair will tend to corrode less. The effect is stronger as the difference in electronegativity is larger. For stainless steels, the orange bars are for the passivated condition and the blue bars are for the sensitized condition. used for steel. One difference is that the melting and processing temperatures are lower for many nonferrous metals than for steel. Thus, the fixtures, dies, and molds used for nonferrous metals can be made of steel in many cases. Some refined nonferrous metals are much more reactive than steel, and so must be carefully protected from exposure to air. In particular, some processing of aluminum (Al), magnesium (Mg), beryllium (Be), and titanium (Ti) is done in vacuum chambers, similar to the tool steels mentioned in Chapter 13. Copyright Goodheart-Willcox Co., Inc.