Journal of Power Sources 188 (2009) 296–300 Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour Short communication Influence of the cooling rate on the ageing of lead–calcium alloys F. Rossi a,∗ , M. Lambertin a , L. Delfaut-Durut b , A. Maitre c , M. Vilasi d a LaBoMaP, Arts et Métiers ParisTech, Rue porte de Paris, 71250 Cluny, France b CEA, centre de Valduc [SEMP, LECM], 21120 Is-sur-Tille, France c SPCTS, UFR Sciences et Techniques, 87060 Limoges, France d LCSM, Université Nancy I, 54506 Vandoeuvre les Nancy, France article info Article history: Received 11 September 2008 Received in revised form 3 November 2008 Accepted 15 November 2008 Available online 21 November 2008 Keywords: Lead–calcium Process parameters Cooling rate Ageing Resistivity Hardness abstract Cast lead–calcium alloys were known to be sensitive to experimental parameters, which cause large variations on the ageing and overageing behaviour. From the study of these parameters, the quenching rate was the only significant parameter. A critical cooling rate was defined based on hardness, electrical resistivity and metallographical observations. The inconsistencies in the literature noticed on the evo- lutions of lead–calcium alloys can now be explained by whether or not this critical cooling rate was respected. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Calcium has been used to significantly improve the mechanical properties of lead by precipitation hardening from an oversaturated  solid solution. Numerous studies have been done on the subject since the replacement of lead–antimony alloys by lead–calcium alloys in the lead-acid batteries [1–4]. Research has dealt with the determination of the mechanisms and the kinetics of harden- ing and softening transformations. The behaviour of the alloy is now well-explained [5] with the identification of five transforma- tions. The hardening was performed in three stages with (Fig. 1): • A: a first discontinuous transformation initiated on the grain boundaries and sweeping the grains. The hardness of the alloy increases from 6 HV (Hardness Vickers) to 10 HV, • B: a second incomplete and approximately 10 times slower trans- formation named “puzzling” lets the hardness increase by 2 HV, • C: a last hardening process with the microprecipitation of Pb 3 Ca (structure L1 2 ) with mean size of 2.5 nm. The maximum hardness is about 15 HV. ∗ Corresponding author. Tel.: +33 3 85 59 53 13; fax: +33 3 85 59 53 70. E-mail address: rossi@cluny.ensam.fr (F. Rossi). The hardening was then followed by two softening transforma- tions (overageing) with (Fig. 1): • D: a coarsening of macroprecipitates aligned in strings. Their growth is due to the progressive dissolution of the thin hardening precipitates (state C), • E: a final softening with the coarsening of the macroprecipitates to form lamellar (Pb 3 Ca) structures. Among the studies on these alloys, many inconsistencies remained during decades on the identification of the transforma- tions. Differences in the observations and interpretations arise on the one hand from the numerous transformations undergone by these alloys and the inherent difficulties in working on lead alloys (soft material and transformations kinetics in a range of several minutes to several years at room temperature). On the other hand, differences in behaviour have been attributed to the sensitivity of the alloy to its chemical composition and its thermal history. We have studied the effect of the process and heat treatment parame- ters on the transformation of the alloy. Experiments were designed to study the effect of each parameter (casting temperature of the alloy, preheating temperature of the mould, temperature of the quenching bath, etc.) [5]. Results have shown that most of the pro- cess parameters had no significant effect on the transformations of the alloy except the quenching rate. This paper is devoted to the analyses of the effect of this main parameter. 0378-7753/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2008.11.049