Lead Alloys

Lead was one of the first metals known to man. Probably the oldest Lead artifact is a figure made about 3000 BC. All civilizations, beginning with the ancient Egyptians, Assyrians, and Babylonians, have used Lead for many ornamental and structural purposes. Many magnificent buildings erected in the 15th and 16th centuries still stand under their original Lead roofs.

Lead-antimony alloys

By far the biggest use of Lead-antimony alloys is in batteries. Trends have varied over the years. At one time, antimony levels of around 10% were common but the current generation of Lead-acid batteries has a much lower level.

Lead-antimony alloys with antimony contents of between 1 and 12% are used widely in the chemical industry for pumps and valves on chemical plants and in radiation shielding both for lining the walls of X-ray rooms and for bricks to house radioactive sources in the nuclear industry.

The addition of antimony to Lead increases Lead's hardness and therefore its resistance to physical damage without greatly reducing its corrosion resistance.

Lead and its alloys in metallic form and Lead compounds are used in various forms of radiation shielding. Their high densities meet the primary requirement of a shielding material and in certain shielding applications Lead's high atomic number is also important. The ease with which Lead can be worked is of added value. The shielding of containers for radioactive materials is usually metallic Lead. Radioactive materials in laboratories and hospitals are usually handled by remote control from a position of safety behind a wall of Lead bricks and X ray machines are normally installed in rooms lined with sheet Lead. Lead compounds are a constituent of the glass used in shielding partitions to permit safe viewing and Lead powder is incorporated into plastic and rubber sheeting as a material for protective clothing.

Several Lead alloys are widely used. Solder, an alloy that is nearly half Lead and half tin, is a material with a relatively low melting point that is used to join electrical components, pipes and other metallic items. Type metal, an alloy of Lead, tin and antimony, is a material used to make the type used in printing presses and plates. Babbitt metal, another Lead alloy, is used to reduce friction in bearings.

Lead Base Alloys

Because Lead is very soft and ductile, it is normally used commercially as Lead Alloys. Antimony, tin, arsenic, and calcium are the most common alloying elements. Antimony generally is used to give greater hardness and strength, as in storage battery grids, sheet, pipe, and castings. Antimony contents of Lead-antimony alloys can range from 0.5 to 25%, but they are usually 2 to 5%.

Lead-Calcium Alloys have replaced Lead-antimony alloys in a number of applications, in particular, storage battery grids and casting applications. These alloys contain 0.03 to 0.15% Ca. More recently, aluminum has been added to calcium-Lead and calcium-tin-Lead alloys as a stabilizer for calcium. Adding tin to Lead or Lead alloys increases hardness and strength, but Lead-tin alloys are more commonly used for their good melting, casting, and wetting properties, as in type metals and solders. Tin gives the alloy the ability to wet and bond with metals such as steel and copper; unalloyed Lead has poor wetting characteristics. Tin combined with Lead and bismuth or cadmium forms the principal ingredient of many low-melting alloys.

Arsenical Lead (UNS L50310) is used for cable sheathing. Arsenic is often used to harden Lead-antimony alloys and is essential to the production of round dropped shot.

Lead-base bearing alloys, which are called Lead-base babbitt metals, vary widely in composition but can be categorized into two groups:

•   Alloys of Lead, tin, antimony, and, in many instances, arsenic
•   Alloys of Lead, calcium, tin, and one or more of the alkaline earth metals

Ammunition. Large quantities of Lead alloy are used in ammunition for both military and sporting purposes. Alloys used for shot contain up to 8% Sb and 2% As; those used for bullet cores contain up to 2% Sb.

Terne Coatings. Long terne steel sheet is carbon steel sheet that has been continuously coated by various hot dip processes with terne metal (Lead with 3 to 15% Sn). Its excellent solder ability and special corrosion resistance make the product well-suited for this application.

Lead Foil, generally known as composition metal foil, is usually made by rolling a sandwich of Lead between two sheets of tin, producing a tight union of the metals.

Fusible Alloys. Lead alloyed with tin, bismuth, cadmium, indium, or other elements, either alone or in combination, forms alloys with particularly low melting points. Some of these alloys, which melt at temperatures even lower than the boiling point of water, are referred to as fusible alloys.

Anodes made of Lead Alloys are used in the electro winning and plating of metals such as manganese, copper, nickel, and zinc. Rolled Lead-calcium-tin and Lead-silver alloys are the preferred anode materials in these applications, because of their high resistance to corrosion in the sulfuric acid used in electrolytic solutions. Lead anodes also have high resistance to corrosion by seawater, making them economical to use in systems for the cathodic protection of ships and offshore rigs.