Metallurgical and electrochemical approach of Pb–(2wt.%)Sm and Pb(0.08wt.%)Ca(2wt.%)Sm lead alloys

The metallurgical study of Pb–2wt.%Sm and Pb–0.08wt.%Ca–2wt.%Sm has been performed from hardness measurements, DSC tests, TEM and SEM observations. It has been shown that the binary alloys do not hardened by microprecipitation of an intermetallic phase such as Pb3Sm: after 2 years, the hardness of Pb–2wt.%Sm alloy is equal to that of pure lead, i.e. 6 HV. Moreover, for Pb–Ca alloy, it appears that the rare earth addition accelerates the three transformations of the ageing. In the simulated overcharge conditions of the acid battery, the Pb–2wt.%Sm grid alloy shows a lower corrosion resistance in 5 M sulphuric acid solution than pure lead. Indeed, the weight loss measured for the binary alloy is increased by 1.5 when it is compared to that of pure lead. This effect is probably due to the grain size decrease and, consequently, to the intergranular corrosion rising for the Pb–0.08%Ca–2.0%Sm with samarium additions in Pb–Ca alloy.