SRUCTURAL HARDENING MECHANISM OF LEAD-CADMIUM-BISMUTH-TIN ALLOYS FOR BATTERY GRIDS

The phenomenon of aging and overaging of Pb-Cd-Bi-Sn alloys is characterized by a discontinuous processing and a continuous reaction, it's hardening and softening. The presence of tin slows kinetics of hardening transformation and increases the hardness. Our study is devoted to determine precipitation type, nature and phase morphology of precipitates and the intensity of hardening in the quaternary alloys Pb-Cd-Bi-Sn. The return to equilibrium of supersaturated alloys Pb-Cd-Sn-Bi has been studied by different techniques: hardness, optical microscopy and X-ray diffraction. Two structural states were considered: raw casting alloy and rehomogenized alloy. The studied alloys are: Pb2% Cd1% Bi, Pb 2% Cd2% Bi, Pb 2% Cd3% Bi with different percentages of tin 0.25% Sn, 0.5% Sn, 1.25% Sn and 2% Sn. Experimental temperatures are 20 degrees C and 80 degrees C. Bismuth accelerates the hardening reaction, while tin has a retarding effect on the hardening process.