Application of Cyclic Polarization of Aluminum 3003 Used in All-Aluminum Microchannel Heat Exchangers
Description: All-aluminum microchannel heat exchangers are designed to significantly reduce refrigerant charge requirements, weight, reduced brazed joints, and decreased potential for leakage by increasing reliability. Al 3003 alloy is corrosion resistant and can be formed, welded, and brazed but the issue with all-aluminum heat exchangers is localized corrosion (pitting) in corrosive environments. Currently, there is no universally accepted corrosion test that all coil manufacturers use to characterize their products. Electrochemical testing method of cyclic polarization was employed in this investigation and relevant parameters including electrolyte corrosive agent and its concentration, electrolyte pH, and applied potential scan rate was varied to find an optimal set of parameters. Results of cyclic polarization of Al 3003 in electrolytes containing various concentrations of NaCl were compared with those of the tests in Sea Water Acidified Accelerated Test (SWAAT) electrolyte and it is shown the SWAAT electrolyte (4.2% sea salt acidified to pH of 2.9) is by far stronger (in terms of corrosivity) than typical 3.5% NaCl solution used in most corrosion testing. Corrosion rates (g/m2yr) of Al 3003 measured in this investigation were comparable to those provided by ISO 9223 standard corresponding to C1 through CX categories. Duration of cyclic polarization test is much shorter than that of SWAAT and results obtained in this test is more reproducible compared to those of SWAAT. Scanning electron microscopy micrographs show typical pit depths of about 50 μm.
Date: May 2015
Creator: Barnes, Javier