A corrosion study of light metal cylinder head material in chloride containing engine coolant environment Anusha Chilukuri, Gaurav Argade, Justin Perry, Corey Trobaugh, Randy Schafer, Erica Raisor, Jacob Steenhoek, Glenia Pena Lugo. Materials Science & Technology, Cummins Inc. Columbus, IN USA Key words: Cast aluminum; Potentiodynamic polarization; Corrosion inhibition; Electrochemical impedance spectroscopy Abstract Room temperature corrosion behavior of cast aluminum-silicon alloy in engine coolant containing proprietary inhibitors in the presence of varying chloride concentrations was investigated. Potentiodynamic polarization curves with chloride contaminated inhibited coolant solutions showed an increase in anodic kinetics with chloride additions from 1000 ppm. A large passive range (with no breakdown till ~ 1 V vs open circuit potential) was observed for chloride concentrations up to 500 ppm suggesting effective inhibition. The pitting potential decreased with an increased in chloride concentration from 1000 ppm to 2000 ppm. Potentiostatic studies at 0.0V vs Ag/AgCl also showed that 1000 ppm is the threshold limit for chloride contamination with an order of magnitude increase in current after three hours of exposure. SEM analysis on the potentiostatic coupons tested in 2000 ppm chloride showed localized pitting and trenching around the silicon particles and intermetallics. 1. Introduction Al-Si-Cu casting alloys have gained popularity in the automotive industry for their many advantageous properties such as high strength to weight ratio, high thermal conductivity, excellent formability, availability, low cost and most importantly, relatively good corrosion resistance when compared to the traditional cast iron engine head and block materials [1-3]. This has made cast Al alloys a preferred choice and this has allowed increased fuel efficiency and reduction in emissions of greenhouse gases [1-3]. Corrosion is a major problem in the engine coolant systems and therefore engine coolants contain several additive packages to combat corrosion. Coolants either have an Organic Acid Technology (OAT) additive package that includes organic acid inhibitors such as sebacic acid, hexanoic acids, etc. or a conventional inorganic inhibitor package that includes borates, silicates, molybdates, phosphates, nitrites, etc. or a combination of both [4]. Hudgens [5] has compared the effect of conventional inorganic additives to the effect of OAT additives on aluminum 319 alloy and concluded that hybrid coolants (organic/ inorganic additive mix) offer a superior combination of life, extended service intervals, and system protection compared to the conventional coolants. Yang et.al. [6] have done extensive electrochemical testing of aluminum alloys (AA 3003 and AA319) in different commercial coolants. Zheludkevich et.al. [7] also used electrochemical techniques to understand the inhibition efficiency of thiazole and triazole additives on AA 2024 alloy. They concluded that these inhibitors showed mixed inhibition by film formation over the intermetallics, thereby retarding both the anodic dissolution and cathodic reduction reactions. There is a gap in the literature in identifying the effectiveness of coolant corrosion inhibition upon its degradation with time and ingress of contaminants while in use. The effective use of electrochemical techniques to aid the identification of threshold limits of several contaminants, most importantly chloride levels, will help the development of the next generation of extended life coolant technologies 1255 Contributed Papers from Materials Science and Technology 2019 (MS&T19) September 29–October 3, 2019, Oregon Convention Center, Portland, Oregon, USA DOI 10.7449/2019/MST_2019_1255_1259 Copyright © 2019 MS&T19®