Alloys like brass weren’t formed out of pure luck. Prior to the first millennium, the technology needed to make brass was primitive at best. The difference in the melting points of copper and smithsonite, also known as zinc spar or zinc carbonate, made it possible to create brass but primarily for decorative purposes.
It was only when copper and zinc were viewed as separate metals did the quest for discovering alloys took off. By the Industrial Revolution in Europe, brass increased in demand. Brass plates provided materials for applications ranging from shipbuilding to agriculture. Still, virtually nobody bothered to ask why copper and zinc made the perfect pair.
To understand this, it’s important to look at brass from a molecular point of view. There are two ways for alloys to work: swapping out some atoms or occupying the gaps between atoms. The phenomena gave birth to substitutional and interstitial alloys, respectively. Brass is the result of the first process, while steel was produced through the latter.
Substitutional alloys are only possible if both metals’ atoms are roughly the same size, inherent among d-block metals or transition metals (except lanthanides and actinides). Copper and zinc, in the periodic table, sit adjacent to each other, with zinc being slightly heavier. Depending on the amount, zinc may replace as much as 35 percent of copper’s atoms.
This tendency of atoms within alloys helps make stronger materials. In substitutional alloys like brass, the added metals change the crystalline structure of the more abundant metal; in this case, zinc “remodels” the copper’s interior. The disparity in atomic size reduces the space in which the plane moves, making the alloy harder and more resilient.
Durability is further determined by the machining process. A solid brass tube, for instance, would be less rigid than a solid brass bar, but the hollow space is necessary for its intended applications. The brass tubing can be cut into smaller, individual pieces for machinery and other industrial products.
Proper metalworking is necessary to prevent a compromise of the alloy. Professional fabricators like Rotax Metals can produce brass in different shapes, like quality square brass tubing, not only to maintain integrity but also to make further processes easier. Indeed, why bore a hole along the length of a brass bar when it’s easier to buy a square tube?
(Source: “Section 9: Modern Materials—Alloys,” Annenberg Foundation)