Why is antimony added to lead in many alloys?

Antimony is added to lead primarily to improve the metal's mechanical properties, specifically its hardness and strength. Because pure lead is relatively soft, the addition of antimony—typically in concentrations ranging from 1 to 8 percent—creates an alloy often referred to as "hard lead" or "antimonial lead".123

This alloying process is essential for several commercial applications:

• Storage Batteries: It is most commonly used for the cast grids and terminals in lead-acid storage batteries, where it provides the necessary structural integrity.1
• Casting and Type Metal: Antimony alloys have the rare characteristic of expanding upon solidification, which allows the molten metal to fill the intricate crevices of casting molds effectively. In type metal, this property ensures sharp definition while increasing the hardness of the type.2
• Industrial Components: The increased strength and hardness imparted by antimony make the alloy suitable for use in pipes, sheets, cable sheathing, ammunition, and various chemical equipment such as pumps and tanks.12

While antimony significantly enhances these physical traits, it is important to note that antimonial lead loses strength at elevated temperatures and is generally limited to applications below 120 °C (250 °F).1