Choi, Don Hyun (School of Advanced Materials Science and Engineering, Sungkyunkwan University) | Ahn, Byung-Wook (School of Advanced Materials Science and Engineering, Sungkyunkwan University) | Quesnel, David J. (Mechanical Engineering Department, University of Rochester) | Jung, Seung-Boo (School of Advanced Materials Science and Engineering, Sungkyunkwan University)
The use of SiC particles placed in AA5083 as a means of controlling the sensitization response that leads to stress corrosion cracking is evaluated using friction stir welding as an innovative tool for creating these alloys. Friction stir welding was performed with a tool rotation speed of 1800 rpm and a tool advance rate of 87 mm/min. SiC powder with a mean particle size of 20 nm was fed into the stirred zone by placing it between the two plates to be welded. The welded specimens both with and without the SiC particles were annealed at 175℃ for 10 days, which has been found previously to produce a well-defined continuous beta phase (Al3Mg2 intermetallic) along the grain boundaries, leading to dramatic stress corrosion cracking and severe responses in the ASTM G67-04 NAMLT (nitric acid mass loss test) evaluation. It was found that the corrosion response in the sensitized state, characterized by the NAMLT, was strongly improved by the nanometer scale SiC particles, which act as nucleation sites for grain interior precipitation, hindering the grain boundary precipitation of the beta phase.
5xxx series Al alloys exhibit good corrosion resistance, especially when Mg is in solid solution or randomly distributed within the matrix as Al3Mg2 particles1. Muller et al.2, for example, found that a Mg content ranging from 1 to 5% in Al-Mg alloys does not influence the pitting potential of the alloy in 1 M NaCl. An alloy with a composition very similar to AA5454 was found to show a pitting potential in 0.1 M NaCl that was only slightly lower than that of very pure Al.3 High Mg content alloys can be susceptible to intergranular corrosion (IGC) when a geometrically continuous intermetallic compound is present along the grain boundaries.