Among the available common engineering alloys, magnesium alloys have the highest strength-to-weight ratio. Use of magnesium alloys in automobiles has been increasing due to the need of increasing fuel economy, reducing pollution and lessening our dependence on petroleum. Recently, several new applications in various parts of vehicles have been developed, including oil pans, gearbox housings, and radiator support assemblies.
However, use of magnesium alloys for vehicle powertrain systems, such as engine blocks, has been quite limited to date. One limitation on the use of magnesium alloys in powertrain systems is their poor corrosion resistance, especially when they are in contact with the water/glycol based heat transfer fluids (coolants) commonly used in vehicle cooling systems.
However, use of magnesium alloys for vehicle powertrain systems, such as engine blocks, has been quite limited to date. One limitation on the use of magnesium alloys in powertrain systems is their poor corrosion resistance, especially when they are in contact with the water/glycol based heat transfer fluids (coolants) commonly used in vehicle cooling systems.
The corrosion inhibitors currently used in water/glycol based heat transfer fluids are formulated with specific blends of silicates, nitrites, mono- or di-carboxylic acids or their salts (such as C4-C18 mono- or di-carboxylic acids, and benzoates), molybdates, nitrates, phosphates, phosphonates, and/or borates to provide corrosion protections for various metals in the cooling systems.
Although many of these inhibitors can provide satisfactory corrosion protection for various metallic components used in vehicle cooling systems (including aluminum, cast iron, steel, copper, brass, and solder), corrosion protection for magnesium alloys is poor. Corrosion rates of the magnesium alloys are especially high when the alloys are in galvanic contact with other metals and/or at high operating temperature (e.g., >90.degree. C.), and in contact with heat transfer fluids not designed for use with magnesium alloys.
Thus, there is a need for new and more effective corrosion inhibitor compositions and corrosion inhibiting heat transfer fluids for use in vehicle cooling systems containing magnesium or magnesium alloys.
Thus, there is a need for new and more effective corrosion inhibitor compositions and corrosion inhibiting heat transfer fluids for use in vehicle cooling systems containing magnesium or magnesium alloys.
In U.S. Patent 7,645,331, Honeywell International Inc. (Morristown, NJ) details nano-silica compositions that inhibit magnesium and magnesium alloy corrosion. According to inventors Bo Yang and Filipe J. Marinho the composition is formed by combining: (a) an inorganic phosphate; (b) a water soluble polyelectrolyte polymer dispersant; (c) a tri or tetracarboxylic acid; and (d) at least one additional component comprising at least one of a C4-C22 aliphatic or aromatic mono- or dicarboxylic acid, a silicate and at least one of a silicone or a silicate stabilizing siloxane compound, and mixtures.
Honeywell also discloses heat transfer fluids that include freezing point-depressing agents; water; and a corrosion inhibitor composition. A method of reducing corrosion in a heat transfer system containing magnesium or magnesium alloy components requires that the system and the magnesium containing components be in contact with the disclosed heat transfer fluid.
Colloidal silica may also be included for use as a corrosion inhibitor in the composition. The colloidal silica has a nominal particle size between about 1 nm (nanometer) to about 200 nm, most preferably, the colloidal silica particle diameter is between about 1 nm to about 40 nm.
Suitable colloidal silicas include Ludox colloidal silica from DuPont or Grace Davidson, Nyacol and/or Bindzil colloidal silica from Akzo Nobel-Eka Chemicals, Snowtex colloidal silica from Nissan Chemical, as well as colloidal silica from Nalco and other suppliers. Another benefit of using colloidal silica in the fluid is that the nanoparticles may increase heat transfer efficiency and/or heat capacity of the coolants. The colloidal silica is present in the formulation in an amount of 1 to about 2000 ppm of the heat transfer fluid.
