Corrosion of novel Pb–Mg–Al–B nuclear shielding alloy in fluoride medium

Five kinds of Pb–Mg–Al–B alloys with B atomic fraction of 0, 1·84, 3·62, 5·36 and 7·06% were prepared by induction melting. The corrosion behaviour of Pb–Mg–Al–B in 3·5 wt-%NaF solution was investigated by immersion tests, neutral salt spray and electrochemical measurements. The surface morphology and corrosion products of alloys were measured using scanning electron microscopy (SEM), X-ray diffraction and X-ray photoelectron spectroscopy. Results show that the Pb–Mg–Al–B alloy with 5·36%B shows the best corrosion resistance; the volume fraction and distribution of Mg₂Pb, Mg₁₇Al₁₂ and other phases affect the corrosion resistance significantly; the major corrosion products are Mg₁₇Al₁₂, Pb, PbO, Al₂O₃, etc., and Mg is apt to form a microgalvanic cell with Mg₂Pb (Mg₂Pb–Mg) in corrosive solution, and a bit of product of MgF₂ film has a role to protect alloys; and the different corrosion resistances are caused by the different microstructure of alloys with different B additions.