A closure device implant for sealing an opening formed through a blood vessel, said closure device comprising a footplate portion at least partially exposed to the lumen of the blood vessel when in use. The footplate portion is formed of a biocorrodible metal comprising a magnesium alloy formulated with a corrosion activator comprising between 0.01% and 0.08% iron, wherein said footplate portion&rsquos magnesium alloy comprises between about 1% to 8.25% aluminium. The magnesium alloy formulated with the corrosion activator is formulated to have a faster corrosion rate in a hemodynamic environment than a corrosion rate of AZ31.
