19: Magnesium, Zinc, Tin, and Specialty Metals

Magnesium has very _________ density

low

Higher temperatures during soldering can produce ____________ on joints in a circuit board.

stresses

Describe the two stages of magnesium alloy precipitation hardening.

1. First, the magnesium parts are solutionized for a short period of time at 700 F in a furnace filled with inert gas or carbon dioxide (to prevent oxidation). 2. The parts are then quenched in air. If aging at room temperature does not add enough strength, the parts can be artificially aged at 300 F for 24 hours. The final parts are much stronger than the original magnesium alloys parts.

How is tin refined?

1. It is extracted from cassiterite, an ore of tin oxide. The ore is recovered by using a dredge or pump mining equipment. It is broken up into gravel and then refined into concentrate. 2. The concentrate is smelted with a mix of metallurgical coal and limestone to form a charge. The charge is heated in a furnace, which reduces the oxide to impure tin. 3. The metal is then reheated in cast iron pots and purified by the introduction of steam or compressed air and a number of other elements. Liquation or electrolytic refining is often used to further purify the metal (until it is almost 99.9% pure). In this condition the tin is cast into ingots for final processing.

How is nickel refined?

1. It is extracted from nickel-rich ores and then refined into pure nickel, ferronickel (alloy of iron and nickel), and nickel oxide. 2. These nickel products are then melted and combined with other metallic elements and alloys to produce nickel alloys. 3. In a molten state, nickel alloys are cast into ingots. To achieve high corrosion resistance, ingots of nickel are typically cast in special vacuum arc furnaces.

How is titanium processed?

1. It is reduced from its ore, rutile, in three stages. The first reduces the ore to sponge, a porous metal. 2. The sponge is then melted into ingots in an electric arc vacuum furnace. Melting must occur in vacuum or inert gas conditions to prevent the presence of gases dissolved in the metal. 2. Ingots are converted into primary products (such as billets) for production of final shapes. Each stage of processing must be closely regulated to ensure high purity of the final product.

Describe some applications of gold

1. excellent for elctroplating removable electronic connectors because it rarely tarnishes or corrodes. Electrical connectors made from copper are often formed into pins and clips. First, nickel is electroplated onto the pins and clips. Then, gold is electroplated onto the nickel plating. An addition of 1-2% cobalt to the gold increases wear resistance of the plating. 2. connections in sold state electronic devices. Because gold does not tarnish or oxidize easily, it is relatively easy to join without a flux or filler metal. Components for electronic chips can be joined by using very small spot welds and gold wires. 3. Gold has very good resistance to oxidation, so it is useful for brazing and soldering alloys. Alloys of gold and nickel and gold and platinum are typically used in brazing. When other metallic elements, such as silver and copper, are added, gold can be used as a soldering alloy. These alloys offer very good resistance to corrosion.

Most jewelry is made from _________ or _________ karat gold for durability.

14/18

Titanium can be formed easily when it is heated above _______________ F. However, what must happen during the forming process?

1400/ titanium reacts readily with air when it is heated, so high-temperature forming procedures must occur in vacuum or inert (shielded) atmospheres.

About _______% of zinc in the United States is recycled from scrap. This is lower than the percentage of recycled ___________ or __________ due to what?

30/aluminum/copper/the volume of zinc used for thin, corrosion resistant coatings. Zinc applied as a protective coating cannot be recycled economically.

Describe the wave soldering process.

A circuit board consists of many copper-plated tracks that carry current from electronic chips to other components. Tin solders can be used to produce mechanical and electrical joints on the board. In wave soldering, the board is passed over the solder so that it just contacts the molten metal. As the solder is pumped from the bath, it flows over a "weir." The flow of solder is similar to the movement of water over the spillway of a dam. The solder "wets" the exposed copper leads, forming the electrical joints. The temperature of the solder must be kept as low as possible because the board components cannot withstand high temperature for very long. Also, the depth and time of immersion must be kept to a minimum.

What are two strong commonly used nickel-based superalloys?

Inconel 600 and Inconel 718.

In what areas can gold be found?

It can be found in the metallic form of fine particles, vein deposits, and nuggets.

What are some safety concerns with magnesium?

It has to be handled very carefully during processing an and other operations for several reasons: 1. At high temperatures, magnesium is a fire hazard in itself. Powdered magnesium burns very easily and can produce a very intense, hot fire. 2. Magnesium should be ground and cut only under the close supervision of a knowledgeable safety expert. Extra care must be taken to prevent sparks from the metal fines. This is true for any type of metal but is very important for magnesium 3. Fires caused by metal are difficult to control. Water cannot be used to extinguish a metal fire. It makes the metal burn more intensely. Only a class D fire extinguisher can be used to extinguish burning metal.

Describe zinc die casting

It has widespread use in commercial applications for several reasons. Zinc melts at a relatively low temperature. It also flows very well when it is molten, so it can be cast into parts with very thin walls and complex shapes. These properties allow for longer use of the casting molds. Lower operating temps help dies retain the smooth surfaces and detail that the designer intended.

Describe electrical solder

It is a mixture of 60%lead and 40% tin and has a low melting point of 361 F. It bonds to copper wire easily to make sound electrical connections. Any surface corrosion that occurs on a properly soldered joint will not disturb the electrical connection.

What is die casting? What advantages does this process present?

It is a process where liquid metal is injected into a die or mold under high pressure to cast a part. Die casting allows a part with many complex details to be molded as one piece.

What is tin?

It is a soft metal that is most commonly used in the production of tin-based solders and for tin plate in food and beverage containers.

What is nickel?

It is a tough metal that has very strong resistance to corrosion and oxidation. It is widely used as an alloying element with metals such as copper, molybdenum, and iron. Nickel is most commonly alloyed with chromium to produce stainless steel.

Describe magnesium

It is a very light metal that is used for small parts and many applications requiring low density and corrosion resistance.

What is gold?

It is a very precious , corrosion resistant metal reserved for special use.

Describe zinc

It is an inexpensive, heavy metal most often used as an alloying element for materials requiring corrosion protection. It is commonly alloyed with aluminum, copper, and titanium for products that can be readily machined or soldered. The most widespread use of zinc, however, involves the surface coating of metals through galvanizing.

How is magnesium refined?

It is electrolytically refined from molten magnesium salts. Magnesium electrolysis is similar to aluminum electrolysis. During refinement, magnesium chloride or magnesium oxide is reduced to magnesium and chlorine or oxygen gas through the introduction of electrical current in a production cell. Since the magnesium is less dense than the molten electrolyte, it floats to the top of the cell for recovery. Large amounts of electricity are needed for the commercial production of magnesium. There are major electrolytic refineries located in the far north of Canadian province of Quebec, where electricity is abundant.

What is gold used for?

It is has been used to make jewelry since the beginning of civilization. Modern uses of gold include casting alloys in dental applications, brazing and soldering alloys, electronic components, and electroplating solutions.

Describe what titanium is used for.

It is limited in commercial applications because it is difficult to extract from rutile (a common mineral of titanium). Titanium processing must be closely controlled to prevent contamination of the metal. For these reasons, titanium is quite expensive as compared to steel or aluminum. Titanium is suitable only for specialized applications where its superior properties are critically necessary.

How is zinc refined?

It is refined from its ore by roasting finely crushed zinc blende (zinc sulfide) or other forms of zinc ore in a furnace. The zinc is converted to vapor in an oxygen-free atmosphere and then condensed into liquid zinc in a container above the roasted ore. Zinc can also be refined electrolytically in processes similar to aluminum and magnesium electrolysis.

Name and describe the most common titanium alloy

R56400, also known as Ti-6Al-4V. It is mad up of mostly titanium, plus 6% aluminum and 4% vanadium. the alloy additions permit great increases in strength through precipitation hardening.

Describe a dual-wave soldering machine

The different chips on a circuit board are soldered in different stages or "waves." The first wave of solder to the circuit board is called the chip wave. It is used to spread rippled solder to the many small surface-mount chips on the bottom of the board. In the second wave, called the delta wave, solder flows all the way up through the holes, making sound electrical and mechanical joints with stuffed chips on the top of the board.

Describe how galvanizing works

The thin layer of zinc that is applied protects the base metal through sacrificial corrosion. In other words, air and moisture corrode the layer of zinc, rather than the base metal. Steel is galvanized by dipping a sheet or metal part into a molten bath of zinc. When the liquid zinc cools, it freezes onto the steel. Large zinc crystals may form on the surface. The zinc keeps the steel rust free until most of the coating has corroded away. If a final coat of paint is applied to galvanized steel, the combination of the paint and zinc increases the overall corrosion resistance of the coating

Describe what solders used to be like for water piping and what they are now.

Tin-lead alloys were formerly used to join water pipes made of copper. 50%tin and 50%lead were useful because they could bond to copper easily. These alloys cooled to a "mushy" condition during freezing, allowing plumbers to remove excess material with a wet rag. Thus, these solders were called "wiping" solders. Tin-lead solders are no longer used for water piping because small amounts of lead can dissolve and contaminate water. Today, lead-free tin solders are required for plumbing applications.

What is a stuffed chip?

a chip that has leads about .100" apart that can be inserted into holes in a circuit board. During wave soldering, the solder will fill the holes to make the electrical joint.

What is wave soldering?

a joining process that uses a low-temperature molten solder bath to connect electronic components in a printed circuit board.

What is titanium?

a low density, corrosion-resistant metal designed for specialized applications. It has a relatively high melting temperature and a high strength-to-weight ratio, so it can be used for parts that must withstand stress at high temperatures. It is commonly alloyed with aluminum, tin, and vanadium to produce strong, lightweight materials.

What is electron beam welding?

a method of welding that uses a beam of high-energy electrons to make weld joints in a vacuum chamber and works very well with titanium. Complex structures can be formed in this process.

Tin normally serves as an ___________ element. It is not ordinarily used as an unalloyed structural material why?

alloying/because it has very low strength at room temperature.

What are solders?

alloys designed to melt at a lower temperature than the melting point of the base metal (the metal being joined).

What other elements can be alloyed with magnesium to impart increased strength?

aluminum, zinc, zirconium, calcium, and occasionally manganese and thorium

Sometimes, ____________ is alloyed to the solder to increase its strength.

antimony

In die casting, sometimes the high force that pushes the liquid metal into the die ends up pushing some metal out through where? What is this called?

between the die halves/This excess metal is called flashing

How can zinc be strengthened?

by alloying it with aluminum and magnesium.

What are intermetallic compounds?

chemical compounds made up of two or more metals that exhibit different properties than the original metallic elements. Intermetallic compounds are specific phases (structures) within an alloy system and are classified separately from other nonferrous metals. These alloys act differently than other alloys because they have precise atomic ratios between the metallic elements and a combination of metallic and ionic bonds.

What are surface-mount chips?

chips that are made with leads that are bent into flat lands that rest on the board surface.

Magnesium is not very ductile, so its strength cannot be improved by _______________ working. How can it be strengthened?

cold/by the addition of alloying elements such as aluminum, zinc, zirconium, calcium, and occasionally manganese and thorium. Strong magnesium alloy parts can be cast, extruded, or hot rolled. Then, they can be machined to the final shape. One of the most commonly used strengthening processes for magnesium alloys is precipitation hardening. Many small machine parts are hardened in this manner

What are some applications of nickel super alloys?

commonly used in the manufacture of aircraft components. At temperatures above 1300 F most ordinary steel oxidizes significantly in a few hours. Even stainless steel cannot survive for long at these temperatures. But nickel can withstand such severe conditions. The superalloys are often used for gas turbine rotor blades in jet engines, where exhaust gases flow at temperatures exceeding 1800 F.

Magnesiums _____________ is lower than that of other metals

ductility

Gold has high ____________ and ___________. It does not _____________ normally, and it can be easily _______________ into different shapes.

ductility/density/tarnish/hammered

Nickel-based superalloys are very __________, and they have little _____________ at room temperature and so the use of coldworking processes to harden these alloys is ______________. Nickel-based superalloy parts such as turbine blades are usually ___________ in a special fashion so that all of the grains in the metal are oriented how?

hard/ductility/impossible/cast/in a long, stressed direction. Cooling methods are controlled to form long, rod-shaped grains in the metal. The final grain structure is very strong and allows the blades to resist elongation at high temperatures.

Magnesium has a high ___________ to ____________ ratio, making it comparable in strength to _______________.

high/weight/aluminum

At room temperature, parts made from zinc alloys may have what properties?

higher impact strength than parts made from cast aluminum and magnesium alloys. They do have higher impact strength than similar iron castings at room temperature and at lower temperatures.

What is a karat and how is it used to determine the percentag of gold in an alloy?

it is a unit of measure equal to one twenty-fourth part of gold in an alloy; the percentage of gold can be determined by multiplying the weight fraction of a sample by 100%. Thus, 14K gold is equal to 14/24, or 58% gold.

The addition of aluminum, and sometime copper, does what to the zinc?

it lowers the melting temperature of it and makes it easier for the alloy to flow into complex shapes.

The resistance of nickel to oxidation at high temperatures makes the metal suitable for what?

jet engine parts and other applications involving hot, corrosive environments.

The weight percentage of gold in an alloy is given in ____________. Pure gold is referred to as ________ karat.

karats/24

When mixed with _________, tin makes an excellent solder.

lead

Most magnesium alloys are not very ductile, so the amount of reduction possible through cold working is ___________. For this reason, many magnesium parts are ______________ to the final shape.

limited/die cast

Name some applications of titanium

many aircraft components and other applications requiring light weight and strength at high temperatures and speeds. Compressor blades in jet engines are commonly made from titanium. Large amounts of titanium is also used in the manufacture of wings for fighter planes. The skin of the wing shown reaches temperatures as high as 300 F.

Tin is a very useful alloying element for what?

metals requiring corrosion resistance and electrical conductivity. Tin alloys are frequently used to manufacture soldering products for used in the electronic and plumbing industries.

What elements are commonly alloyed with gold? For what purpose?

nickel or copper/to increase its strength and resistance to wear.

Magnesium, zinc, and tin are often used for ________________ metallurgical applications

nonferrous

Gold is an expensive metal because of its _____________.

rarity

Titanium can be welded if it is what?

shielded with an inert gas cover or welded in a vacuum.

Pure gold is very ________ and _________ when it is rubbed against ones skin.

soft/wears

Specialized nickel alloys strengthened to resist corrosion and high stresses at extreme operating temperatures are known as what?

superalloys.

What is galvanizing?

the application of zinc to coat a metal and protect it from corrosion. In this process, a thin layer of zinc is applied to steel sheet, strip, or wire.

What is porosity?

the presence of internal pores caused by trapped air or gas.

It is impossible to use solutionizing or other heat treatment processes with ________ alloys. Why?

tin/because the melting point of the alloy is so low that even at room temperature, the metal behaves the way other metals do at high temperature.

Tin is most commonly electroplated onto steel to produce what?

tinplate (steel coated with tin).

The force applied by the ram on the liquid zinc when die casting must be high enough for what?

to ensure that the casting is sound and free of porosity.

What is tinplate used for?

to manufacture metal cans for foodstuffs and containers for other products, such as paint. The addition of tin protects materials from reacting with the steel of the can. Tinplate accounts for the greatest percentage of commercial tin production.

What are the uses of intermetallica compounds?

various uses because of their behavior that is unique to the alloy system. For example, Al₂Cu, an intermetallic compound of aluminum and copper, is not ductile (like aluminum and copper is) and also not very conductive. When titanium reacts with nitrogen, it forms titanium nitride (TiN). This is a very hard, wear-resistant compound that can be applied as a coating on cutting tools and selected abrasives. Titanium aluminide (TiAl₃) is a compound of titanium and aluminum. This alloy is much harder and more resistant to wear than both titanium and aluminum. For this reason, titanium aluminide is commonly used in the manufacture of automobile engine valves.