INTRODUCTION TO ENGINEERING MATERIALS - NONFERROUS METALS - PART 4

Audio: Introduction to engineering materials – nonferrous metals – part 4

In our introduction to engineering materials series, we discussed the first group of ferrous metals. In part 1, we discussed the classification of engineering materials and why it is important to choose the proper material. Then, we investigated the plain carbon and low alloy steels. Furthermore, in part 2, we discussed stainless, tool, and specialty steels. In part 3, we finished the ferrous metals by discussing the cast irons. In this article, we will look into a new group of metals you may use, the nonferrous metals.

Introduction

As a mechanical design engineer, you must choose the materials for every part you design. There is a large number of different materials that you could choose based on their properties, manufacturability, cost, and the component’s function. In the introduction of the engineering materials series with part 3, we finished the first subgroup of metals – ferrous metals. We will now move to nonferrous metals and look into the primary engineering materials and how they can be used in our day-to-day work.

Even though ferrous metals are used in larger quantities due to their wide range of mechanical properties, high manufacturability, and affordance, nonferrous metals are more advantageous for specific uses due to their specific properties. Nonferrous metals include metal elements and alloys that are not based on iron.

Nonferrous metals: Aluminum and its alloys

Aluminum is a light metal, and it is abundant on Earth (3^rd most plentiful element on Earth). The principal aluminum ore is called bauxite. The aluminum symbol is “Al”; it has atomic number 13 and FCC crystal structure. The most often alloying elements are copper, magnesium, manganese, silicon, and zinc.

Aluminum has high electrical and thermal conductivity, excellent strength-to-weight ratio, and excellent corrosion resistance. It is a very ductile metal that does not show a ductile-to-brittle transition at low temperatures and is easily formable. Because of aluminum’s low melting temperature (660°C), aluminum does not perform well at elevated temperatures. Furthermore, aluminum has low hardness, leading to poor wear resistance. The mechanical properties of aluminum can be enhanced by cold work and alloying. However, both processes reduce corrosion resistance.

It is used for containers, wrapping foils, electrical conductors, pots and pans, parts for construction, aerospace, automotive, and other uses in which lightweight is essential.

We can divide aluminum alloys into wrought and cast alloys. Wrought alloys are shaped by plastic deformation, and cast alloys are shaped by casting.

The most important wrought aluminum alloys are aluminum-manganese, aluminum-magnesium (non-heat-treatable), aluminum-copper, aluminum-magnesium, and aluminum-zinc (heat-treatable) alloys.

The most important cast aluminum alloys are aluminum–silicon, aluminum-copper, and aluminum-magnesium alloys.

Example of wrought aluminum alloy:

EN	Material number	AISI
AW - 2017A	3.1325	2017

AW-2017A is aluminum wrought alloy with 3,5% – 4,5% copper content and 0,4% – 0,8% magnesium with addition of some other elements. It has intermediate strength, good ductility, and corrosion resistance is fair. It is used for pulleys, gauges, knitting needles, rivets, screw machine products, fasteners, general structural components, aircraft components, etc. It has excellent machinability, and it can be welded.

Example of cast aluminum alloy:

EN	Material number	AISI
-	-	319.0

319.0 is aluminum cast alloy with 3% – 4% copper content and 5,5% – 6,5% silicone with addition of some other elements. It has intermediate strength, good ductility, and corrosion resistance. It is used engine crankcases, gas and oil tanks, engine oil pans, engine parts, bushings, brackets, covers, cases, etc. It has excellent casting and machining characteristics. It can be welded.

Nonferrous metals: Beryllium and its alloys

Beryllium is a light metal with a lower density than aluminum. It is mainly extracted from a mineral called beryl. The beryllium symbol is “Be”; it has atomic number 4 and an HCP crystal structure. It is primarily used as a pure metal, beryllium oxide, or as an alloy with copper, aluminum, magnesium, or nickel.

Even though that beryllium is lighter than aluminum, it is stiffer than steel. It has high thermal stability and thermal conductivity. Furthermore, it is brittle, reactive, and toxic. Unfortunately, beryllium is expensive, and it is used in specific industries.

Beryllium and its alloys are used in inertial guidance systems, aerospace applications (high-speed aircraft, guided missiles, spacecraft, satellites), nuclear applications, etc.

Nonferrous metals: Magnesium and its alloys

Magnesium is the lightest structural metal. It is mainly extracted from seawater. The magnesium symbol is “Mg”; it has atomic number 12 and an HCP crystal structure. It can be alloyed with aluminum, manganese, zinc, beryllium, and other rare Earth elements.

Due to the low density and good strength-to-weight ratio, magnesium is interesting, where weight plays a significant factor. At room temperature, magnesium and its alloys are difficult to deform. Magnesium has a relatively low melting temperature (651°C). It is highly susceptible to corrosion in a marine environment, while corrosion resistance is fairly good in a normal environment. Magnesium has a low modulus of elasticity, poor fatigue resistance, creep, and wear. It also is hazardous during casting and machining since it combines easily with oxygen and burns.

Up to 90% of magnesium alloys are produced as castings. It is used in aerospace, missiles, bicycles, chain saw housings, luggage, and other applications in which lightweight is a primary requirement. For example, magnesium is now employed in a variety of hand-held devices (e.g., chain saws, power tools, hedge clippers), in automobiles (e.g., steering wheels and columns, seat frames, transmission cases), and in audio-video-computer-communications equipment (e.g., laptop computers, camcorders, TV sets, cellular telephones).

Example of magnesium alloy:

EN	Material number	AISI
MCMgZn 4 RE 1 Zr	3.5101	ZE 41

ZE 41 is magnesium alloy with 3,5% – 5,0% zinc content, 0,4% – 1% zirconium, and 0,8% – 1,7% of rare earth elements. It has intermediate strength and corrosion resistance. It is used for aircraft components, military equipment, video cameras, motorcycle wheels, power tools, helicopter gearboxes, etc. It has excellent casting and machining characteristics. It can be welded.

Nonferrous metals: Copper and its alloys

Copper is one of the oldest metals known. It is mostly extracted from ore chalcopyrite. The copper symbol is “Cu”; it has atomic number 29 and FCC crystal structure. It can be alloyed with aluminum, zinc, beryllium, tin, silicon, and nickel.

Pure copper has a reddish-pink color, and the most distinguished engineering property is low electrical resistivity (widely used as an electrical conductor). Furthermore, copper is an excellent thermal conductor, and it is corrosion-resistant. The strength and hardness of copper are relatively low.

Copper’s properties can be enhanced with alloying. Bronze is an alloy of copper and tin (90%Cu and 10% Sn), and brass is an alloy of copper and zinc (65%Cu and 35%Zn). The highest strength alloy of copper is beryllium-copper (about 2% Be).

Copper and its alloys are usually used for electrical conductors and components, ammunition (brass), pots and pans, jewelry, plumbing, marine applications, heat exchangers, springs (Be-Cu), etc.

Example of copper alloy:

EN	Material number	AISI
CuBe2	2.1247	C17200

CuBe2 is a copper alloy with 1,8% – 2,0% beryllium content and some other alloying elements. It has very high strength and stiffness with good conductivity. It is used for electrical/electronic connectors, current-carrying springs, precision screw machined parts, washers, retaining rings, welding electrodes, bearings, plastic molds, corrosion resistant components (valves, pump parts), etc.

Nonferrous metals: Titanium and its alloys

Titanium is relatively abundant in nature (about 1% of Earth’s crust). It is mostly extracted from ore rutile. The titanium symbol is “Ti”; it has atomic number 22 and HCP crystal structure. It can be alloyed with aluminum, tin, vanadium, copper, and magnesium.

Pure titanium is reactive, leading to processing problems, especially in a molten state. Titanium has a relatively low thermal expansion coefficient and low density. It is stiffer and stronger than aluminum and retains good strength at elevated temperatures. At room temperature, it has exceptional corrosion resistance.

Titanium is mainly used in a pure state or alloyed. In the pure state, it is used for corrosion-resistant components and prosthetic implants and alloyed is used where an excellent strength-to-weight ratio is required at elevated temperatures. We can divide titanium into several categories:

commercially pure titanium,
alpha titanium alloys,
beta titanium alloys, and
alpha – beta titanium alloys.

They are commonly used in airplane structures, space vehicles, surgical implants, and the petroleum and chemical industries.

Example of titanium alloy:

EN	Material number	AISI
ATI 6-6-2™	3.7175	R 56620

ATI 6-6-2™ is a alpha-beta titanium alloy with 5% – 6% aluminum content, 5% – 6% vanadium, 1,5% – 2,5% tin and some other alloying elements. It has very high strength. Typical applications are airframe and jet engine parts, rocket engine cases, and ordnance components. It can be machined and welded.

Nonferrous metals: Lead and its alloys

Lead is mainly extracted from ore galena. The lead symbol is “Pb”; it has atomic number 82 and FCC crystal structure. It can be alloyed with tin and antimony. Lead is a dense metal with a low melting point, low strength, hardness, high ductility, and good corrosion resistance. It is usually used as solder, for ammunition, x-ray shielding, storage batteries, vibration damping, etc.

Nonferrous metals: Tin and its alloys

Tin is mostly extracted from ore cassiterite. The tin symbol is “Sn”; it has atomic number 50 and HCP crystal structure. It can be alloyed with lead and copper. Tin has a low melting point, low strength, low hardness, and good ductility. Tin is used as an alloying element to form bronze. It is also used for tin-coated sheet steel containers (“tin cans”) and as solder.

Nonferrous metals: Zinc and its alloys

Zinc is mostly extracted from ore sphalerite. The zinc symbol is “Zn”; it has atomic number 30 and HCP crystal structure. It can be alloyed with aluminum, copper, and magnesium.

Zinc is a hard and brittle material; and a fair electricity conductor. It is mostly used in die casting to mass produce components for automotive and appliance industries and galvanized steel (corrosion protection coating onto steel). Also, zinc is used as an alloying element to form brass.

Nonferrous metals: Nickel and its alloys

Nickel is mostly extracted from ore pentlandite. The nickel symbol is “Ni”; it has atomic number 28 and FCC crystal structure. It can be alloyed with aluminum, copper, iron, and chromium.

Nickel is magnetic and has virtually the same elasticity modulus as iron and steel. It has high corrosion resistance and great high-temperature performance. It is mostly used as an alloying element in steel and as a plating metal on other metals. Nickle is used as an alloying element for forming Alnico magnets.

Refractory nonferrous metals

Refractory nonferrous metals are metals that have extremely high melting temperatures. In this group are niobium (Nb), molybdenum (Mo), tungsten (W), and tantalum (Ta). In addition to high melting temperatures, these materials possess high elastic modulus, strength, and hardness. For us, the most interesting are molybdenum and tungsten.

Molybdenum is extracted from ore molybdenite. The molybdenum symbol is “Mo”; it has atomic number 42 and BCC crystal structure. It is relatively dense, stiff, and strong. It is used both as pure metal and as an alloy. Molybdenum and its alloys are used for heat shields, heating elements, electrodes for resistance welding, dies for high-temperature work, extrusion dies, parts for rocket and jet engines, etc.

Tungsten is extracted from ores scheelite and wolframite. The tungsten symbol is “W”; it has atomic number 74 and BCC crystal structure. It possesses the highest melting temperature of any metal (3410°C) and is also the hardest and stiffest of all pure metals. It is used for parts for rocket and jet engines, incandescent light filaments, x-ray tubes, electrodes for arc welding, etc.

Precious metals

Precious metals, also known as noble metals, include gold, silver, and platinum. As a group of nonferrous metals, they possess high density, good ductility, high electrical conductivity, and good corrosion resistance.

The gold symbol is “Au”; it has atomic number 79 and FCC crystal structure. Gold is one of the heaviest metals but is soft and easily formed. It is used for making jewelry, electrical contacts, dental works, plating onto other metals, etc.

The silver symbol is “Ag”; it has atomic number 43 and FCC crystal structure. Silver has the highest electrical conductivity of any other metal. It is used for coins, jewelry, tableware, fillings in dental work, electrical contacts, etc.

The platinum symbol is “Pt”; it has atomic number 78 and FCC crystal structure. Platinum is more expensive than silver and gold. It has high density, corrosion resistance, and catalytic characteristic. Platinum is used for jewelry, thermocouples, electrical contacts, spark plugs, corrosion-resistant devices, catalytic pollution equipment, etc.

Superalloys

Superalloys contain a substantial amount of three or more metals. They are a group of high–performance alloys designed to meet requirements for high strengths and corrosion and oxidation resistance at high temperatures.

We can divide them into three groups:

iron-based alloys,
nickel-based alloys, and
cobalt-based alloys.

These metals are widely used in gas turbines, jet and rocket engines, steam turbines, nuclear power plants, etc.

Closing words

In this article, we covered a wide range of different nonferrous metals. There are many more that we did not mention that were not extremely important to be included here. Depending on which industry you work in as a mechanical design engineer, some materials will be more important than others. Keep in mind that with experience comes the trap of not looking for new, better, and less expensive material solutions.

In the introduction to engineering materials series, in part 1 and part 2, we covered steels. In part 3, we covered cast irons, and in this part, we finished the nonferrous group of metals. All this together covered the whole introduction to the metals. We are continuing with an introduction to engineering materials, so in the next post, read about engineering ceramics.

Now you have an excellent overview of nonferrous metal types you could encounter as a mechanical design engineer. However, I suggest you go through the text once more and identify areas you think need more understanding and clarity. Then, once you have identified those areas, start building up your knowledge in those areas.

To make it easier for you to find related posts, check the “Further reading” chapter below. Do you have any questions or need something to be clarified better? Leave a comment below, and I will give my best to adjust the post accordingly.

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