Studies on chrome free galvanic conversion coating on magnesium alloy AZ31B for space applications

Abstract A novel galvanic conversion coating was studied on magnesium alloy AZ31B in an electrolyte system consisting of ammonium molybdate and magnesium chloride. The conditions of the conversion coating process and the characteristic of the coatings are studied in detail. The coatings were characterised by energy dispersive X-ray, infrared spectral and scanning electron microscopy studies. The thermoanalytical investigations have been carried out using thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC). The space worthiness of the coating was evaluated by environmental tests, namely, humidity, thermal cycling, thermovacuum performance and thermal stability tests. Optical properties (solar absorptance and infrared emittance) were measured before and after each environmental test to ascertain its stability. The coating provides higher solar absorptance and infrared emittance in the order of ∼0·80. The developed procedure is simple, ecofriendly and economically viable.