US2040078A - Lead alloy - Google Patents

Description

1 m in the low PatentedMay 12, 1936' .IUNITED sTATEs PATENT OFFICE a ,040,078

mammals Wellington.

No Drawing.

Application November Serial No. 007,144

ilmnanl'. Kaiser,

z Claims. (01. 75-100) ifirantednnderthoactoflifarchs,

This invention relates to an alloy of lead and strontium. It has among its several objects to produce a compomtion of the type mentioned that will have desirable features of mechanical,

6 strength and hardness and resistance to disintegration when subjected to the action of an electric current while immersed in electrolyte.

Our invention is especially adapted for use in making grids for the plates of storage batteries 10 although its usefulness is by no means limited thereto. Usually the grids of both the positive and negative plates of storage batteries are made of lead to which to of antimony has been added to impart the requisite. strength and hardness. While the effect of the antimonyis satisfactory in the respects mentioned, it has a number of disadvantages.

I One such disadvantage is that the composition specified does not freeze into a homogeneous mass but first segregates crystals of lead which, if "un-' disturbed, fall to the bottom of the melt. Finally,

when the proportionof antimony in the still fluid portion of the metal rises to 13%, due to depletion ofthe lead by crystallization, the remainder of additional undesirable feature is that the antimony of the positive gridis carried, during the "process of charging, into the activematerial (spongy lead) of the negative electrodes where it produces local plate.

40 we have found that the alkaline earth meter strontium,.in certain proportiona produee's a de-.

sirable degree of in lead and doesnot have the disadvantages cbnnected with the use i of antimony. Itforms an insoluble sulphate and therefore is ot-P e t inappreciable amounts i in the electrolyte and can not-give rise to local action. v

Useful hardeni V tained by means of this metal whenit is pr s nt hardening alloys with lead. By'this is meant that the hardness isobtained through a special heat treatment the theory of which follows! 7 action and sulphation of of the can not be ob-" percentages in which it forms so id solutions in the lead, but it forms precipitatic ia in lead at a high temperature, near the melting point, than its does at room temperature. when an alloy having a composition of about the percentages in which solid solutions are formed is V slowly-cooled to room temperature the original 5 complete solidification is followed by the precipitation of minute crystals of an intermetallic compound of lead and the alloying metal within the body of solidified metal. The crystals so produced do not add significantly to the hardness of 10 the lead. If, however, the same alloy is quenched suddenly from the high temperature, the atoms of the alloying metal are trapped in solid solution but still are not very effective in imparting hardness. If, following this quenching, the lead is allowed to age for several days either at room temperature, or perhaps better at a somewhat elevated temperature below the melting point, extremely minute and evenly distributed crystals of the compound are formed which, due to their small size and even distribution, impart a marked degree of strength to the alloy. For in-. stance, 0.08% of strontium, added to pure lead gives an alloy which after quenching from 300 C. and aging for three weeks at 100 C. has a Brinell hardness of from '7 to 9 which is a de sirable hardness for storage battery grids. We have found further that alloy so prepared and treated is not attacked by oxygen .to an appreciably greater degree than the antimony alloys.

I An alloy of lead containing 0.5% strontium and 0.2% tellurium is very resistant to intergranular corromon, the presence of the tellurium l at the grain boundaries rendering these regions 35 more stable. The Brinell hardness of this alloy is .'l.9 both before and after steam corrosion. In addition, the presence of tellurium lowers the sol ubility of gases in the melted alloy so that a casting is more free from blow holes due to bubbles o of escaping gas than is acastine made with the alkaline earth metal and lead alone.

, Alloys of lead with 0.04% to 0.20% strontium maybe hardened by quenching from a temperature not far below the freezing point followed by 4.5 aging at e peratures ranging from room temperature to somewhatbelow the melting point and-are sumciently resistant to corrosion to be suitable for storage battery grids and while the alloy is largely eutectic has much as 0.5% stronso tium is used, it is still well adapted for that use. when tellurium is usedv the percentage of strontium may vary between 0.2% and 0.6% and the tellurium between 0.1%- and 0.5%.

the term "balance consisting substantialb purposes, without the payment of lead is meant that elements other than lead in the portion so designated do not substantially exceed 1 per cent 01' the total alloy. 7 The invention described herein may be manuiactured and used by or for the Government of the United States 01' America forv governmental thereon.

We claim: V 1. An alloy comprising 0.04% to- 0.6% strontium and the balance co substantially oi 0! any royalties lead, said alloy being characterized by even distribution of minute crystals of the alloy, a desirable degree of hardness, stability at the grain boundaries, low solubility of gases when in the molten condition and high resistance to intergranular corrosion and attack by oxygen.

2. An alloy comprising 0.04% to 0.6% strontium, 0.1% to 0.5% tellurium and the rest lead.