The pitting corrosion behavior of rapidly solidified aluminum alloys

Abstract

The effects of rapid solidification and alloying on the pitting corrosion resistance of binary and ternary aluminum alloys containing Mg, Ti, Mn, Cr, Fe, Ni, Cu, Zn, Zr, Nb and/or Si in deaerated 0.5 N NaCl at 30°C have been investigated. Rapid solidification by melt spinning is quite effective in ennobling the pitting potential by several hundred millivolts for all alloys except for those containing Mg, Fe or Zn. In addition to the ennoblement of the pitting potential, rapid solidification decreases both the anodic and cathodic current densities with a consequent decrease in the open circuit corrosion rate. The pitting corrosion attack of conventionally cast alloys generally takes place in the α-Al phase adjacent to the cubic silicon and/or intermetallic compound phases except for AlNiSi alloys in which the Al 3Ni phase is preferentially attacked. Rapid solidification leads to the formation of the α-Al phase supersaturated with solute atoms and to either complete elimination or significant decrease in amount of the silicon and intermetallic compound phases. The ennoblement of the pitting potential and enhancement of the open circuit corrosion resistance due to rapid solidification are attributable to the reinforcement of the α-Al phase by supersaturation with solute atoms and the elimination or decrease in amount of the silicon and intermetallic compound phases responsible for preferential corrosion attack.