Soft Metals: Aluminum, Brass and Copper
Elemental aluminum is soft and highly malleable, making it a poor candidate for mechanical purposes. Instead, aluminum is usually blended with a mix of other elements, including silicon, copper, magnesium, and zinc, then heat-treated to make the strong, lightweight alloys used today in airframes, automobiles, and various consumer products.
PT’s machining service makes parts from two types of aluminum: 6061-T6 and 7075-T6. The T-suffix signifies how the material was processed, in this case mechanically stretched by 1 to 3 percent after heat treatment to eliminate residual stress, thus making it more stable when machined. 6061 aluminum is alloyed with magnesium and silicon, and in its wrought form offers yield strength of 40,000 psi or more. It is very corrosion resistant and weldable given the proper equipment, making it an ideal choice for low-fatigue applications such as structural components in machinery, hydraulic valve bodies, marine, and automotive parts, and most any application requiring robust, lightweight material.
Aluminum component machined on a 3 aixs
Copper Components Finished by CNC
Rounding out the soft metal lineup are brass and copper, the kissing cousins of the metal family. Of the two, brass is by far the most versatile. With the exception of environments high in ammonia and some acids, it is extremely weather and corrosion resistant. If you’ve ever replaced a car radiator, soldered a kitchen faucet, or played the French horn, you’ve handled parts made of brass.
PT offers parts machined from C260 brass, which contains 70 percent copper and 30 percent zinc, and is considered the most general purpose of all brass alloys. There are literally dozens of brass grades though, all with subtle differences and distinct uses.
To a machinist, brass is as easy as it comes. It is sturdy stuff, offering tensile strength rivaling that of mild steel. Ironically, copper is a far different story. Even though it’s the primary ingredient in brass, unalloyed copper’s machinability is roughly five times worse, and even the most patient of machinists avoid it due to copper’s tough, stringy nature. Chips are virtually impossible to break and, due to its high thermal conductivity, the material heats up very quickly during cutting.
Copper is only second to silver in electrical conductivity, a factor that makes it one of the most important metals in use today. Copper (and aluminum) wiring basically make electricity possible. Without it, lights would remain unlit, cars wouldn’t run and it would be impossible to blend a frozen margarita.
Copper is easy to braze but difficult to weld. Its extreme ductility makes it both strong and flexible, a rare occurrence among metals. Yet copper does far more than conduct the power needed to heat our grills. It’s used in semiconductor manufacturing as an element of high-temperature superconducting, in glass-to-metal seals such as those needed for vacuum tubes, and has even been approved for use in hospitals and public places as an antimicrobial surface.
Hard Metals: Steel, and Stainless Steel
That world needs hard metals as well. Steel is used in everything from cars to cruise ships, cables to crescent wrenches. Regardless of alloy type, steel is mostly composed of iron. Iron smelting and limited steel manufacturing has been in use for thousands of years, but it wasn’t until the Bessemer steel process, invented in the mid-1800s, that mass production of high-quality steel was made possible. Thus began the industrial revolution.
As with the soft metals, a small quantity of alloying elements can have a dramatic effect on steel’s properties—the addition of less than 1 percent carbon and manganese, along with a little metallurgical legerdemain, is what makes brittle iron into tough 1018 steel. And 4140 alloy steel, suitable for aircraft use, is made by combining an equally small amount of chromium along with a dusting of molybdenum.
Carbon steels such as these can be hardened to one extent or another, and are easily welded. There’s just one problem: They rust, making plating or painting a requirement for most any application involving carbon steel.
The 300-series stainless steels offered by Precise Technic carry at least 20 percent chromium along with a fair amount of nickel, making them more difficult to machine. Still, these popular materials are commonly used for medical instruments, vacuum and pressure vessels, and for food and beverage equipment. 300-series stainless is quite tough, but cannot be hardened like carbon steel. If hardness is a requirement for your application, consider kicking it up a notch with 17-4 PH.