Abstract
This work determined the microstructure and tensile properties of low-calcium Pb-Sn-Ca alloys (with a tin-to-calcium content ratio ranging from 18.4 to 23.5) used to produce positive lead-acid battery grids. Natural aging during storage under atmospheric conditions resulted in a breakdown of the supersaturated alpha-lead solid solution, with (Pb,Sn)₃Ca and Sn₃Ca strengthening particles precipitating. A noticeable change in grain size was not observed in the tested alloys aged for 32 days. The Pb-Sn-Ca alloys age-strengthened rapidly after casting, requiring 32 days to reach an average of 2.7, 4.9, and 1.3 times greater ultimate tensile strength, yield strength, and Young's modulus, respectively. The data obtained showed that the prolongation of aging time produced stronger and stiffer materials, but the average elongation of the alloys became 2.4 times lower. Age-strengthening mainly occurs during the first 15 days of natural aging.

Key words
lead-acid batteries, positive grids, lead-tin-calcium alloys, natural aging, stress-strain diagrams, tensile properties

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