Precipitation in lead-calcium alloys containing tin
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I.
INTRODUCTION
THE precipitation from supersaturated ce solid solution in Pb-Ca binary alloy is known to cause significant age hardening.V,2] This hardening occurs in two stages by discontinuous precipitation; one is rapid and the other is very slow.[ 3~] The commercial Pb-Ca alloys for a maintenance-free storage battery contain Sn. t7] However, there are a few studies ts,gi on the precipitation in Pb-Ca-Sn ternary alloys. Myers et al. ts] reported that the addition of 0.5 and 1.0 pct Sn to Pb-0.1 pct Ca (wt pct) alloy inhibited hardening during aging. Borchers and Assmanntga found by metallographic and hardness measurements that the addition of Sn retarded discontinuous precipitation and continuous precipitation occurred preferentially when the Sn additions exceeded the threefold atom quantity of Ca. Borchers further suggested that continuous precipitates such as Sn3Ca were formed. Previously, we have reportedtl~ that the precipitation in Pb0.04 pct Ca-l.2 pct Sn alloy takes place by a continuous mode, and it has been suggested that the precipitates are not Sn3Ca but in the form of (Pb,Sn)3Ca. In this report, precipitation in Pb-0.04 to 0.08 pct Ca alloys containing various amounts of Sn has been studied, mainly by means of resistivity measurements and transmission electron microscopy (TEM) observations. II.
EXPERIMENTAL PROCEDURE
Pb-Ca-Sn alloys were prepared by the same method as reported previously.[lOl Calcium and tin contents in the alloys determined by Inductively Coupled Plasma (ICP) analysis are shown in Table I. The specimens for metallography and hardness measurements were plates of about 10 x 5 X 3 mm 3, and the specimens for electric resistance measurements were wires 1.8 mm in diameter and about 60 mm in length.
H. TSUBAKINO, Professor, Faculty of Engineering, S. IOKU, Researcher,TEM Laboratory,and A. YAMAMOTO,AssociateProfessor, are with the Department of Materials Science and Engineering, Himeji Institute of Technology,Hyogo 671-22, Japan. M. TAGAMI, formerly Student, Department of Materials Science and Engineering, Himeji Institute of Technology,is with YonekuraCo., Ltd., Osaka 554, Japan. This article is based on a presentation made during TMS/ASM Materials Week in the symposium entitled "Atomistic Mechanisms of Nucleationand Growthin Solids," organizedin honor of H.I. Aaronson's 70th Anniversaryand given October3-5, 1994, in Rosemont,Illinois. METALLURGICALANDMATERIALSTRANSACTIONSA
Specimens were solution annealed at 568 K for 3.6 ks in an air furnace for metallographic observations and hardness measurements and in a vacuum furnace for resistivity measurements, quenched into iced water, and then aged isothermally. The aging was performed in silicon oil baths kept at constant temperatures (To) in the range 303 to 473 ___ 0.2 K. Hardness was measured with a micro-Vickers hardness tester, applying 0.245 N load. Measurements were made at grain boundary and at grain center regions of each specimen. The resistance of the specimens during aging was measured using the four-probe potentiometric tec
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