Nickel-boron plating on magnesium and AZ91D alloy by a chromium-free electroless process

摘要

Ni-B coatings have been deposited directly on commercial purity magnesium and AZ91D magnesium alloy by a chromium-free electroless process and characterized using scanning electron microscopy, glow discharge optical emission spectroscopy, gravimetric measurements and, for corrosion evaluation, hydrogen evolution. The surfaces of the coatings reveal a typical cauliflower-type appearance and form at a rate of ~8 to 13μm/h. The nickel and boron contents of the coatings are relatively uniform across the whole thickness. The addition of NH _4HF _2 to the electroless bath improves the corrosion resistance provided by the coatings during immersion of coated substrates in sodium chloride solution.