Effects of casting mold temperature on tensile properties of Pb–Sn–Ca alloys for negative grids of lead-acid batteries

Abstract In this work grain structure and tensile properties of as-cast and aged Pb–Sn–Ca alloys (with tin-to-calcium content ratio ranged from 2.6 to 3.3) used to produce negative grids for lead-acid batteries were determined. The microstructure of the alloys was studied by scanning microscopic and quantitative metallographic analyses. Mechanical properties in terms of ultimate tensile strength, yield strength, Young’s modulus, and elongation were estimated at room temperature using TIRAtest 2,300 universal testing machine. Based on the tensile test results, average stress-strain curves for aged Pb–Sn–Ca alloys were plotted for the subsequent age-strengthening analysis. The studies showed that the significant casting process parameter was the mold temperature that markedly affected grain structure of the alloys. With mold temperature rising from 60 °C to 170 °C, an average grain size was increased by as much as two-fold. As a result, elongation increased by 55 %, but ultimate tensile strength decreased by 25 %. Ageing time affected grain structure of the alloys to a much lesser degree since the change in average grain size was negligible. Strengthening occurred rapidly within first 3 days of ageing during storage at ambient temperature. With ageing time prolonged up to 35 days no appreciable differences in the tensile properties’ values were found.