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

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 13 μm/h. The nickel and boron contents of the coatings are relatively uniform across the whole thickness. The addition of NH4HF2 to the electroless bath improves the corrosion resistance provided by the coatings during immersion of coated substrates in sodium chloride solution.

► A new electroless bath for coating magnesium with Ni–B layers is reported. ► The electroless process is chromium-free and does not employ HF. ► Deposition of uniform, continuous layers is demonstrated. ► Effects of bath composition on deposition and corrosion resistance are shown. ► Compatibility of the process with coating of alloys is revealed.