COPPER ALLOYS

Copper alloys enjoy a reputation as widespread as the metal itself in its pure form, and their use is practically balanced: about half of the extracted copper is used directly, while the other half is transformed into alloys that improve its mechanical, chemical, and structural properties. Among these, bronze occupies a preeminent place, not only due to its historical and cultural significance, but also due to its superior technical qualities compared to most brasses. Although copper-nickel alloys can surpass bronze in certain aspects, their classification depends on which of the two metals acts as the base, while in bronze and brass, copper is undisputedly the dominant force.

Copper, on its own, is a soft, ductile, and malleable metal, too "soft" for demanding structural applications. Therefore, it has been alloyed for thousands of years to increase its toughness. Although it is not known with certainty when or where the first bronze pieces were produced, it is known that the alloy of molten copper and tin was discovered millennia before Christ, resulting in a material stronger than its individual components. Tin, identified as responsible for the enhanced properties of bronze, became a strategic resource, even encouraging Roman expansion into northwestern Europe, particularly into the region of "Albion," a name that could allude to the "white metal" (albus in Latin) in reference to tin, historically more important in the British Isles than silver.

Cornwall, in southwest England, is traditionally considered the epicenter of tin mining and high-level smithing, at a time when steel had not yet dominated the scene. The Romans had copper available, but needed tin to make bronze, which explains their interest in colonizing Britain. Interestingly, the descendants of those colonized peoples would become conquerors centuries later, as did the Spanish and French in America and Africa, respectively. Even today, the United Kingdom maintains a steady supply of mineral resources from the Horn of Africa, reflecting a strategy inherited from history's greatest conquerors: the Romans.

In the United States, bronze does not enjoy the same popularity due to the relative scarcity of tin, while zinc is abundant. This explains why "brass" is more common than "bronze," which is primarily associated with statues and ornamental pieces, or is called "red brass." Brass is the second most important copper alloy, and in some countries, such as the United States, even the main one. It replaces tin with zinc, with typical contents of 10–12% and maximums that can reach 45% by mass. Its golden color, similar to that of gold, makes it especially attractive in decorative applications, and its mechanical properties are also remarkable. Tin, being more expensive than zinc, is reserved for special alloys.

Currently, there are copper alloys that contain similar proportions of tin and zinc—for example, 5% of each—which complicates their classification. Since there is no universal standard that precisely delineates what constitutes bronze and what constitutes brass, the two terms are often used interchangeably. However, it is most correct to consider bronze those alloys where tin exceeds 5% by mass and is the primary alloying agent, above zinc, nickel, or manganese. Other compositions are classified as brass. Although the name may seem less prestigious, brass is a high-quality alloy, costing more than steel and nickel-free stainless steels.

There are exceptions to this unwritten rule. Copper alloys with aluminum, beryllium, or manganese—even though they contain little tin—are called aluminum bronze (or cuproaluminum), beryllium bronze (or beryllium copper), and manganese bronze, respectively. These names are due to the fact that the primary alloying agent is not zinc, nickel, or tin, but rather the specific metal that defines their properties. On the other hand, the most important copper alloy that does not fall into the bronze or brass category is cupronickel, which comes in several grades and is distinguished by its excellent corrosion resistance, especially in marine environments, and its thermal stability, making it a prime choice for naval, thermal, and electrical applications.