Preparation And Properties Of Aluminum And Aluminum Alloy Coatings Electroplated From Inorganic Molten Salt

Aluminum and aluminum alloys are well known for their comprehensive applications in steel protection. However, as the standard potential of Al is much lower than that of hydrogen, aluminum and its alloys can only be electrodeposited in an absolutely non-aqueous system. In this essay, aluminum and its alloy electroplating were carried out in an inorganic molten salts consisted of aluminum chloride, sodium chloride and potassium chloride.Structure and properties of layers obtained at different temperature, time and current densities in different molten salts were tested and analyzed by XRD, SEM, Scratch and electrochemical testing methods. The results demonstrated that in 150℃when AlCl₃:NaCl: KCl (wt %) was 78:11:11, high quality layers can be obtained at current densities ranged from 3.3 to 4.0A/dm². Pure Al coating was in a uniform, fine-grained needle-like shape with a silvery white morphology. The thickness of Al layer was proportional to escalated current densities and times. Adhesions between the layer and the substrate were entirely beyond 30N, and presented a trend of inversely proportionate to current densities and times. The corrosion resistance of pure Al deposition was preferable to low carbon steel substrate, which can be estimated by the polarization impedance Rp. In this experiment, Rp values of Al layers obtained at different parameters were all larger than 2000?·cm2, while the substrate was only 800?·cm2. The data shown that pure Al layer can provide the substrate a well-protected effect.In order to optimize the properties, MnCl2 and MoCl5 were added into the molten salts to deposit aluminum-manganese and aluminum-molybdenum alloys. Al-Mn alloy layers was appeared in a dendrite or amorphous structure, which was determined by the Mn content in the alloy layer; while the Al-Mo alloy surface took on a granule state that was not very compact. XRD curves explained that the structures of alloy layers were made up of solid solution or amorphous state, which were determined by alloy contents in the layers. Polarization impedance of Al-Mn layers were greater than 4×104Ω·cm². That was nearly ten times greater than Al layers. The corrosion resistance of Al-Mn layers in 3.5% NaCl, 0.5mol/L H₂SO₄ and 1mol/L NaOH solutions were proved to be better than Al layers too. The Rp of Al-Mo is probably...