STP1556

    Improved Aluminum Passivation for Heavy-Duty Coolants

    Published: Jul 2014


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    Abstract

    To improve the energy efficiency of combustion engines, lightweight materials are being used in modern vehicle designs. As a consequence, aluminum is increasingly being selected as an additional metallurgy in cooling systems including heat-exchanger applications. Different brazing techniques can be used to assemble heater core components during construction of aluminum heat exchangers. Controlled atmosphere brazing (CAB), using potassium aluminum fluoride flux material is increasingly being used. Field reports, together with laboratory investigations, have confirmed that flux residues are partly soluble in coolant formulations and the findings indicate that the dissolved substances can interact with coolant additives, resulting in a loss of performance. Depending on the coolant chemistry, field experiences range from simple color changes from pH shifts to overheating, because of additive instabilities or even corrosion damage. Others have studied interactions of flux residues with coolants using different methods; this paper uses an alternative test method to evaluate the effects of CAB brazed aluminum heat exchanger materials to correlate with field observations. Parameters monitored for the study included changes in the physical chemical properties, additive stability and corrosion-protection performance of the test fluids. The study focused on heavy-duty coolants with different additive technologies, including nitrite-containing and nitrite-free formulations. The results clearly demonstrate that the field observations, mainly originating from the interactions with reactive aluminum surfaces, can be simulated using this test method. A novel additive chemistry has been developed and was added to the different coolant formulations, enabling a reduction or even elimination of the typical field observations. The adapted chemistry not only resulted in a more stable pH, but also reduces the consumption of corrosion inhibitors including nitrites and silicates. As a result, these coolant formulations are more robust and the concentration of coolant additives, to obtain the appropriate metal protection levels, are maintained.

    Keywords:

    coolant, aluminum, controlled atmosphere brazing, flux, heat exchangers, radiators, nitrites, silicates, heavy-duty, passivation


    Author Information:

    Claeys, Sandra
    Global Coolants Technology, Chevron Technology Ghent, Gent/Zwijnaarde,

    Lievens, Serge
    Global Coolants Technology, Chevron Technology Ghent, Gent/Zwijnaarde,

    De Kimpe, Jurgen
    Global Coolants Technology, Chevron Technology Ghent, Gent/Zwijnaarde,

    Van de Ven, Paul
    Global Coolants Technology, Chevron Technology Ghent, Gent/Zwijnaarde,


    Paper ID: STP155620130066

    Committee/Subcommittee: D15.21

    DOI: 10.1520/STP155620130066


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