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• Describe safety procedures for working with all the light metals.
• Identify commercial applications of the light metals, including
magnesium, beryllium, and lithium.
• Describe casting processes used to produce magnesium parts.
Learning Objectives
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• Explain why hot-chamber die casting is the most common casting
method for magnesium.
• List the major safety precautions for working with parts and
components that contain beryllium alloys.
• Understand why lithium is not used for applications that require part
strength.
Learning Objectives
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• Light metals are characterized by two properties.
• Very low density
• High reactivity
• Useful for lightweight, especially moving, structures.
• Magnesium (Mg), beryllium (Be), and lithium (Li)
Introduction
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Periodic Table of Elements
Goodheart-Willcox Publisher
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• Chief characteristic of light metals is their density.
• Selected properties of three low-density metals are shown here,
with iron and aluminum included for comparison.
Property Comparison
Goodheart-Willcox Publisher
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• Magnesium (Mg) is a very low-density metal used for applications
requiring low mass.
• Strength comparable to aluminum on pound-for-pound basis
• Used for pivoting arms in computer hard disk drives
• Less arm weight means more accurate head positioning.
• Used for precision robot arms, such as pick and place machines for
circuit board assembly
Magnesium
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• Magnesium has hexagonal close-packed (hcp) crystal structure.
• Ductility is less than bcc or fcc metals.
• It has many applications as castings.
• It has very few applications that require cold forming.
Magnesium (cont.)
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• Magnesium is electrolytically refined from molten magnesium salts.
• Magnesium oxide is precipitated from seawater or brine solutions with
limestone.
• Then converted to magnesium chloride with hydrochloric acid
• Oxide or chloride is reduced to magnesium and chlorine or oxygen
gas.
• Uses an electrical current (like aluminum reduction).
Extraction of Magnesium
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• Magnesium is less dense than molten electrolyte.
• It floats to top of electrolytic cell.
• Liquid metal is removed and cast into small ingots of pure
magnesium.
• Liquid metal oxidizes rapidly.
• It must be handled under an inert cover gas (argon).
Extraction of Magnesium (cont.)
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• Major magnesium electrolysis refineries are located in northern
Quebec Province, where hydroelectricity is abundant.
• Most magnesium produced in North America is refined with renewable
energy.
• Resulting low-density magnesium helps reduce fuel consumption for
moving vehicles.
Magnesium Refineries
Sustainable Metallurgy
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• Magnesium alloy ingots can be rolled to flat sheet.
• Ingot temperature must be kept high during hot work.
• Hcp metals have fewer slip planes for deformation.
• Less ductile than fcc or bcc metals
• Bulk deformation only possible near melting point, so amount of cold
work is limited
• Metal strengthening is done mostly through alloy additions.
• Many magnesium parts are cast and then machined to shape.
Production
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• Besides hot-rolling, magnesium can be
extruded and forged.
• Workpiece must be kept at high
temperature.
• Extruded magnesium rails are shown
here.
Bulk Deformation
Mag Specialties, Inc.
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• Magnesium is cast by several methods.
• Die casting (also called pressure die casting)
is most common.
• Sand casting
• Permanent molds
• Hot-chamber die casting is used.
• Eliminates entrapment of skull in finished
parts
• With its lower melting point, magnesium does
not erode steel dies.
Casting
Goodheart-Willcox Publisher
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• Magnesium alloys require less energy to
melt than aluminum.
• Casting cycles can be faster.
• Liquid magnesium fills narrow spaces.
• Fills walls as thin as 0.040″ (1 mm)
• Smooth finish and near net shape of
magnesium die castings are an added
advantage.
Advantages of Die Casting Magnesium
Chicago White Metal Casting, Inc.
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• Magnesium is highly flammable.
• Casting operations require strong safety precautions.
• Hot-chamber die casting uses flux or atmosphere cover.
• Shields liquid metal from air better than cold-chamber method
• Metal is better protected against oxidation.
• Reduces risk of metal fire
Reduced Risk with Hot-Chamber Die Casting
Safety Note
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• Magnesium is well suited to semisolid die casting.
Thixomolding Magnesium
Molded Magnesium Products, LLC
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• Thixomolding machines use vacuum
and sealed chambers.
• Protects hot magnesium chips
• Cast metal has finer microstructure,
less alloy segregation, and less
shrinkage porosity.
Thixomolding Machine
Goodheart-Willcox Publisher; Molded Magnesium Products, LLC
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• Magnesium machines somewhat like aluminum.
• It is usually cut dry, with small feed rates and high surface speeds.
Machining Magnesium
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• Because of fire risk, magnesium should be ground and cut only
under supervision of a safety expert.
• Extra care must be taken to prevent sparks near metal fines.
• Although true for all metal, these precautions are critical for
magnesium.
Safe Machining
Safety Note
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• Strength of magnesium can be increased
by adding alloying elements.
• Aluminum, zinc, rare earths, or certain
other metals
• Some magnesium alloys are designed to
be strengthened through precipitation
hardening.
• Precipitates are small and function by
resisting dislocation motion.
Strengthening by Heat Treatment and
Alloying
socrates471/Shutterstock.com
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• Some alloys are strengthened by precipitating intermetallic particles
during casting.
• Particles are larger than those developed by precipitation hardening.
• The particles form primarily along grain boundaries.
• Large particles are less effective than small precipitates.
• The particles formed during casting remain effective as
temperatures rise.
Strengthening Cast Alloys
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• General principles of precipitation hardening apply.
• Heated to put alloy components into single-phase solution
• Quenched to form supersaturated solution
• Finally, age hardened
• Naturally aged at room temperature (T4 temper) or artificially aged at
elevated temperatures for 24 hours (T6 temper)
• Same temper designations as aluminum
Precipitation Hardening Magnesium
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• This magnesium alloy is strengthened by precipitation hardening.
• Parts solutionized at 700°F (370°C) in furnace with inert gas or CO2
• Parts quenched in forced air
• Water or oil not used due to rapid corrosion and threat of fire
• Aged to harden
• Room temperature for T4 temper; at 300°F (150°C) for 24 hours for
T6
• Heat-treated alloy is stronger than as-cast or forged equivalents.
Example of UNS M16600 (ASTM ZK60A)
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• Time to reach solutionizing temperature is
almost twice as long for cast magnesium
as for wrought magnesium.
• Done to prevent partial melting (liquation)
• Effect is most significant in slow-cooled
sand castings.
• Forged parts must not undergo liquation.
• If forged while partially molten, they would
be ruined.
Heating to Solutionizing Temperature
DmitryBirin/Shutterstock.com
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• Pure magnesium will creep and deform under load at 225°F
(107°C).
• Creep strength is improved by adding elements that form hard
precipitates at grain boundaries during casting.
• Grains cannot slide past one another easily.
• Precipitates will not dissolve during high-temperature use.
• Precipitates maintain strength and reduce creep at higher
temperatures.
Creep Strength
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• These large grain-boundary precipitates reduce ductility
significantly.
• They are usually used for cast products only.
• Magnesium alloy UNS M17620 (AJ62A) contains aluminum,
calcium, and strontium.
• The additions increase strength.
• The additions reduce creep for engine blocks and transmission
housings.
Creep Strength (cont.)
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• Mechanical properties of magnesium alloys depend strongly on
production methods used.
Mechanical Properties
Goodheart-Willcox Publisher
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• Magnesium must be handled very carefully.
• At high temperatures, magnesium is a fire hazard.
• Dry powdered magnesium can catch fire from a hot spark.
• Moist powdered magnesium may catch fire all by itself.
• Machined magnesium chips, fine particles, and dust are fire hazards.
• Fires caused by magnesium are difficult to control.
• Water only makes metal burn more intensely.
• Only a class D fire extinguisher can extinguish burning metal.
Working Safely with Magnesium
Safety Note
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• Beryllium is obtained from beryl by a complex chemical processing
sequence.
• This produces beryllium chloride (BeCl2).
• Beryllium metal is electrolytically refined from the chloride.
• Beryllium reacts in air to form oxide film in microseconds.
• Like aluminum, film prevents further room-temperature oxidation.
Beryllium
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• Beryllium metal has hexagonal
close-packed crystal structure.
• Bulk deformation can only be done
at high temperatures.
• Cold work of beryllium is not
possible.
Beryllium Metal Properties
Bjoern Wylezich/Shutterstock.com
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• Very high modulus of elasticity (beryllium is most rigid metal)
• Beryllium is used for inertial navigation devices.
• They need a rigid, invariant reference to establish position.
Beryllium Metal Properties (cont.)
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• Solid metallic beryllium is not especially harmful.
• Small number of people are allergic to beryllium oxide (BeO) powder.
• Beryllium oxide dust causes berylliosis, which reduces lung capacity.
• Strict precautions must be used to avoid inhaling beryllium fines, dust, or smoke.
• Precautions needed where beryllium metal is cut, sawed, ground, polished
• Respiratory masks, air venting, vent hoods, and dust collectors are necessary.
• Use recommended protective clothing and avoid carrying dust out on shoes or
clothing.
Beryllium Health Hazards
Safety Note
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• Mirrors for James Webb Space Telescope are
made of gold-coated beryllium in hexagonal
sections.
• Each hexagonal plate must be aligned with others
once in space.
• High modulus of elasticity minimizes distortion due
to mounting stresses or other loads.
• Beryllium can handle extreme cold better than
glass.
• Expected temperature is 33 K (–400°F, or –240°C).
Application in Space
Alex Mit/Shutterstock.com
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• Small size of beryllium atoms makes
it nearly transparent to X-rays.
• Thin beryllium sheets are used as
radiation windows on X-ray tubes.
• Thermal conductivity of beryllium
oxide is almost as high as aluminum
metal.
Beryllium X-ray Windows
GE Healthcare
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• Beryllium oxide is also an excellent electrical insulator and is used
in power rectifiers.
• Electrical devices that convert AC power to DC power and are used
for welding, railroad traction motors, and similar electrical power uses.
Beryllium Power Recitifiers
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• Never cut into a power rectifier without a safety data sheet (SDS).
• You must know that the power rectifier does not contain beryllium
oxide (BeO).
• There is no hazard in handling assembled, encased rectifiers.
Handling Rectifiers
Safety Note
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• Least dense of all metals at room temperature
• Low melting point, 356.90°F (180.50°C, or 453.65 K)
• Effectively at its hot-working temperature at room temperature
• Room-temperature mechanical strength is low.
• Strong electronegativity and low density make lithium an excellent
lightweight battery material.
• Use of lithium-ion batteries for mobile devices has increased
dramatically.
Lithium
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• Lithium may be obtained from pegmatite, a coarse form of granite.
• Today, most lithium is obtained by extracting lithium salts from brine
in natural seas or from leaching rock ores.
• Major sources are in South America.
• Desert regions in Chile
• Andes Mountains in Argentina and Bolivia
Sources of Lithium
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• Brine is evaporated in salt ponds and chemically processed to a
mixture of lithium and potassium chlorides.
• Lithium is refined by electrolysis from melted chloride salts.
• Electrowinning is the recovery of metal from solution by electrolysis.
• Lithium metal floats to top, is removed, and is poured into small
ingots.
• Lithium is more reactive than magnesium.
• Liquid metal must be shielded from air.
Lithium Electrowinning and Refinement
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• Lithium metal is soft at room temperature.
• It can be extruded easily.
• Rolling is possible, if rolled surfaces are cleaned frequently to prevent
them from picking up metal fines and oxide scale during rolling.
Lithium Processing
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• Lithium reacts easily with both nitrogen and oxygen.
• If lithium sits in room air, it forms a dark lithium nitride compound
(Li3N) in a few minutes.
• This must be removed before the metal can be extruded or used in
batteries.
• Storage is usually done in mineral oil, or in vacuum-packed
containers.
Lithium Processing (cont.)
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• Lithium metal is highly reactive.
• Water vapor or liquid causes reaction with atmospheric gases.
• Reaction causes heat, which can ignite hydrogen-air mixtures with
explosive force and also result in a cloud of hazardous gas.
• Safe operating procedures to avoid contamination and ensure safe
breathing are essential.
• Any production area involving lithium metal or batteries
Caution with Lithium (Part 1)
Safety Note
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• Burning lithium on a sandstone rock will react with the silica in
sandstone and burn even more intensely.
• Anyone who has seen lithium burn into a concrete floor understands
lithium fire hazards.
• Like magnesium and aluminum, lithium burns more vigorously if
water is put on it.
• Only class D fire extinguishers can put out lithium metal fires.
Caution with Lithium (Part 2)
Safety Note
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• Lithium is very electronegative and has a very high energy-to-weight
ratio, making it useful in batteries.
• A lithium electrolytic cell produces about 3 volts.
• Compare this to 1.5 volts for a zinc-carbon cell.
• The density of lithium is 0.54 g/cc, slightly over half that of water.
• A zinc-carbon battery has an overall density in excess of 3 g/cc.
Applications: Batteries
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• Lithium metal batteries, called lithium
batteries, are not rechargeable.
• Lithium-ion batteries are rechargeable.
• Both types of batteries use lithium, but
they have different chemistry.
Applications: Batteries (cont.)
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• Electric vehicles depend on lithium-ion
batteries.
• Many other devices and energy storage systems
do also.
• All lithium and lithium-ion battery production
must keep lithium metal shielded from air during
construction.
• It is hermetically sealed in final products.
• Shown here is the battery configuration of an
electric automobile.
Lithium-Ion Batteries for Electric
Vehicles
3DMI/Shutterstock.com
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• Despite some contradictory reports, the US Geological Service estimates
there is enough lithium ore to power a majority of the world’s automobiles
for the foreseeable future.
• For consumers, lithium-ion batteries promise to sharply cut gasoline and
diesel fuel consumption.
• This will reduce vehicle operating costs and benefit the environment.
• The energy required to produce lithium-ion batteries is less than the energy
of the fuel they save.
Lithium-Ion Batteries
Sustainable Metallurgy
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• All low-density metals discussed in this chapter are very reactive.
• Their powders ignite easily, making a very intense, high-temperature fire
that is difficult to extinguish.
• Large solid blocks are less hazardous but cannot be treated lightly.
• These metals present fire hazards when processed near their melting
points.
• They should be ground and cut only under supervision of a safety expert.
• Extra care must be taken to prevent sparks near metal fines.
Safe Use of Reactive Metals
