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

摘要

A novel galvanic conversion coating was studied on magnesium alloy AZ31B in an electrolytesystem consisting of ammonium molybdate and magnesium chloride. The conditions of theconversion coating process and the characteristic of the coatings are studied in detail. Thecoatings were characterised by energy dispersive X-ray, infrared spectral and scanning electronmicroscopy studies. The thermoanalytical investigations have been carried out using thermo-gravimetry (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 (solarabsorptance and infrared emittance) were measured before and after each environmental test toascertain its stability. The coating provides higher solar absorptance and infrared emittance in theorder of ～0.80. The developed procedure is simple, ecofriendly and economically viable.