Development of Oxidation Resistance Coating on Tungsten Based Electrical Contacts of Automotive Disk Type Electromechanical Horn

In electromechanical horns, electrical contacts made out of tungsten are generally used to connect and disconnect the electrical circuit. Tungsten is used for this application due to its high melting point, high hardness, good abrasion & wear resistance. However, due to tungsten’s poor oxidation resistance, these electrical contacts undergo severe high-temperature oxidation during contact making and breaking. Thus, development of high-temperature oxidation-resistant coatings on tungsten contact under different pack composition such as concentration of master alloy (15 – 40 % Al for aluminizing and 30 - 40% Cr for chromizing), activators (2 - 5 % NaF /NH4F for aluminizing, 2 - 5% NH4I / NH4Cl for chromizing) and fillers (55 – 83 % calcined alumina/ calcined alumina + chromium for aluminizing, 55 – 68 % of standard compound known China clay) at different temperature (750 - 1100 °C for aluminizing, 900-1200 °C for chromizing) for different soaking time (5-15 for aluminizing, 18-24 for chromizing) inside constant hygon (95 % Ar + 5 % H2) environment is attempted. Effect of above-mentioned parameters on coating behaviour such as coating thickness, composition, structure and hardness is reported in this research paper. By optimizing the above-mentioned parameters Aluminizing coating at 750 °C for 10 h soaking time with 15% Al powder source as master alloy, 3 % NaF as activator and 82 % calcined alumina as filler resulted into 15 - 20 μm coating thickness, single phase – WAl3.5 structure throughout coating having average micro-hardness of 550.4 HV0.05. Chromizing coating at 1200 °C for 24 h soaking time with 40 % Cr powder source as master alloy, 3 % NH4I as activator and 57 % China clay as filler resulted into 25-30 μm coating thickness, gradient phase change of structure from Cr9.6FeW0.9 to Cr6.5Fe5.3 from outer to inners side of coating having average micro-hardness of 751.5 HV0.05 Keywords: Automotive, Horn, Tungsten, Aluminizing, Chromizing, Oxidation, Resistance, Coating, Electromechanical Horn, Vehicle horn, Materials, Mechanical Forces, Scanning Electron Microscope, DOE, Coating