WL 112 Ch16 ch16 presentation

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Metallurgy
Fundamentals
Ferrous and Nonferrous

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.
• Describe the desirable properties of aluminum alloys.
• Understand the properties that make aluminum a preferred choice
for heat sinks.
• Explain how alloying, cold-working, and precipitation hardening are
used to change the properties of aluminum.
• Identify applications of aluminum alloys in daily life.
• Understand the methods for joining aluminum and their applications.
Learning Objectives

• Aluminum is the most widely used nonferrous metal.
• Aluminum alloys have many desirable properties.
• High strength-to-weight ratio
• Good strength
• Good corrosion resistance
• High electrical and thermal conductivity
• Aluminum can be easily formed.
• Aluminum can be joined by most joining methods.
Introduction

• In North America, most aluminum is
refined from ore.
• About one-third is remelted from scrap.
• Aluminum is extracted from bauxite, an
abundant ore.
• It contains aluminum oxide plus iron
oxide, silica, and titanium dioxide.
• Aluminum oxide is extracted from
bauxite by the Bayer process.
Extracting and Refining Aluminum from
Ore and Scrap
Goodheart-Willcox Publisher

• Aluminum oxide is dissolved in molten cryolite (a salt).
• An electric current reduces aluminum oxide into aluminum.
• It oxidizes carbon blocks into carbon dioxide.
• It produces 1.5 lb (0.7 kg) of CO2 per lb (0.45 kg) of aluminum metal.
• Aluminum metal (pot metal) collects and is cast into pigs.
• Pigs are shipped for use elsewhere.
Converting Ore into Aluminum with
Electricity

• Effects of mining bauxite and refining metal must be considered.
• Extracting aluminum oxide from bauxite produces red mud, a finely
ground, alkaline sludge of sand and iron oxide.
• It must be put somewhere, usually holding ponds to settle.
• It must be monitored to prevent it from spilling into streams and rivers.
• Difficult to stabilize, red mud is not useful in construction.
• As one solution, mine pits in Australia have been rehabilitated into self-
sustaining native forests.
Dealing with Red Mud
Sustainable Metallurgy

• Aluminum sources can be mill scrap, manufacturing scrap, or
postconsumer scrap.
• Scrap is grouped by similar compositions, called alloy families.
• The parts of beverage cans are slightly different alloys in one family.
• Cans are easily recycled.
• About 55% of aluminum cans are recycled.
Aluminum from Recycled Scrap

• Recycling aluminum saves 90% of the energy used to produce
aluminum from ore.
• Approximately 31% of aluminum produced in the United States
today comes from recycled scrap.
Recycled Aluminum

• Pot metal and scrap are melted in large furnaces.
• This is poured into a ladle, where alloy additions are made.
• Then it is poured into a mold.
• For sheet and plate production, drop molds and continuous casting
molds are used.
Remelting and Pouring to Ingots

• Drop molds are 5′ (152 cm) by 2′ (65 cm), with vertical walls only
18″ (50 cm) high.
• Mold walls initially surround a chill plate.
• Liquid metal is poured through filters into molds.
• Chill plate, holding solid aluminum, is lowered at same rate as liquid
metal is poured in.
Drop Mold Casting

• Some aluminum is poured by continuous
casting.
• A strand as much as 6″ (15 cm) by 24″ (61 cm)
thick is dropped from the mold.
• A “flying saw” cuts strands into lengths before
reaching bottom of casting pit.
Continuous Casting

• Aluminum and its alloys are identified by number designations
developed by Aluminum Association (AA).
• Wrought alloys are identified by four-digit number.
• First digit identifies major alloying element.
Aluminum Alloy Classifications

• Unified Numbering System (UNS) parallels AA designations.
• A9 indicates wrought aluminum alloy, A0 indicates casting alloy.
• Last four digits match AA numbering system.
Unified Numbering System (UNS)

• A single value represents the maximum allowable content.
Composition of Selected Aluminum
Alloys

• After cooling, sides of ingots are usually milled to remove rough cast
surfaces.
• Ingots go to a soaking pit and are heated for hot-working.
• When hot, ingots are taken to a breakdown mill.
• Breakdown mill reduces ingots to billets and plate.
Bulk Deformation of Aluminum

• Powered rollers move hot ingot into
breakdown mill rolls.
• Operator controls motion and
reduction amount on each pass.
• Large rolls break ingots down from
24″ (61 cm) to 4″ (10 cm) thick.
Hot-Rolling Plate and Sheet
Arconic

• Slabs are reheated and reduced to about 1″ (25 mm) thick.
• Roll stands further reduce 1″ plate to 3/8″ (9.5 mm) thickness.
• Strip is coiled, cooled, and shipped or further cold-rolled.
Hot-Rolling Plate and Sheet (cont.)

• Recently, Arconic (spinoff of Alcoa) brought a
micromill online.
• It produces aluminum sheet for automotive market.
• Finished sheet takes 20 minutes from pour to coil,
compared with 20 days for traditional process.
• Rapidly cast and rolled metal has improved
microstructures.
• Micromill aluminum has 40% more ductility and 30%
higher strength than traditional auto body sheet.
Advanced-Technology Production
Arconic

• Aluminum plate and billets are forged more easily than steel.
• Properties improve as metal is worked, just as for other metals.
Forging
Karolis Kavolelis/Shutterstock.com

• Aluminum ingots up to 10″ (25 cm) in
diameter and 5′ (1.5 m) long are
extruded into complex shapes.
• Heated to hot-work temperature and
placed in extrusion press
• Ram pushes metal through die into
shapes like those shown here.
• Process operates at lower
temperatures, which increases die
life.
Extrusions
Jay Warner; MMXeon/Shutterstock.com

• Hot-rolled aluminum strip may be annealed before cold-rolling,
completely recrystallizing it and restoring high formability.
• Coils of aluminum strip are annealed in large ovens.
• Nearly 23 hours to reach annealing temperature of 600°F (316°C)
• Depending on required final properties, strip may be given
intermediate or final anneals.
• Final thickness 0.010″–0.040″ (0.254–1 mm) or less
Cold-Rolling

• Rolling aluminum foil requires special
rolling mills.
• A Sendzimir mill is used to do this.
• Invented by Polish engineer and inventor
Tadeusz Sendzimir, who was granted
more than 100 patents in mining and
metallurgy.
Rolling Aluminum Foil

• Small aluminum tubes are made by drawing
larger tube through reducing dies.
• Both outside and inside diameters are
reduced simultaneously.
Drawing
Thiti Sukapan/Shutterstock.com

• Aluminum cans are made from flat sheet.
• Drawn into cup shape
• Sidewalls ironed (thinned) into can shape
• Can production line makes multiple cans
per second.
• Variation in formability may cause damage
and serious delays.
• Metal for cans must be carefully
manufactured and consistent.
Ironing to Produce Cans
Goodheart-Willcox Publisher; Jay Warner

• Aluminum powder is first compressed into
a green compact, then sintered to
become a dense solid.
• Particles of aluminum powder have
surface oxide.
• Sintered aluminum contains uniform
dispersion of oxide particles, which
increases compression strength of
sintered compacts.
Powder Metal (PM) Parts
Allied Sinterings, Inc.

• Aluminum powder burns if struck with flame or spark.
• Once burning, it reacts with anything containing oxygen.
• Aluminum powder reacts with water, releasing hydrogen.
• Released hydrogen burns in air.
• Aluminum powder must be treated as a flammable substance.
• Store in flame-proof containers
• Type D fire extinguishers must be used to extinguish a metal fire.
Use Caution with Aluminum Powder
Safety Note

• Sand and steel molds need small relief angles on certain sides.
• Allows pattern or molded part to be removed
• Steel molds also usually need die relief agents to aid removal.
Casting Aluminum

• Lost-foam casting does not need a
die relief angle or agent.
• Aluminum is used to make
explosion-proof containers.
• Critical for housing electrical
switches near flammable gases
Casting Aluminum Applications
Larson Electronics

• Casting alloy AA360 (UNS A03600) is used
for about one-half of all die cast alloys.
• Pressure fills very fine detail and matches
surface finish of die.
• Cooling rate is very high.
• Die cast parts have fine grain structure,
resulting in good strength.
• Die casting can turn out about one part per
minute.
Die Casting, or Pressure Die Casting
Warut1/iStock

• Aluminum sand and permanent mold castings tend to contain small
pores.
• Volume reduction as aluminum solidifies is greater than for other
metals.
• Hot isostatic pressing closes and heals voids and pores.
• HIP for two hours at 14.5 ksi (100 MPa) pressure and 960°F (515°C)
• Results in higher minimum strength and improved part-to-part
consistency
HIP to Improve Properties

• Aluminum is strengthened using one or
more processes.
• Cold-working, alloying, and precipitation
hardening
• These methods improve strength, ductility,
and dent resistance.
• Type and extent of strengthening process
is called the temper.
Strengthening Aluminum

• Cold forming is primary strengthening
method for AA1XXX, 3XXX, 4XXX, and
5XXX alloys.
• These alloys cannot be precipitation
hardened.
• Cold work results in reduced ductility.
• Alloys in H18 temper (fully cold-worked)
cannot be folded over without cracking.
• For formability, alloys usually supplied as
H14 (half hard) temper.
Cold-Working
Modine Manufacturing Company

• Work at temperatures between cold work
and hot work produces stronger metal
than full anneal.
• Also retains sizable amount of ductility.
• For example, alloy AA5154-H14 is made
this way.
• It has excellent formability, weldability,
and good strength.
Producing Strength and Ductility
MWCPhoto/iStock

• Highest strength is obtained with precipitation hardening.
• Three families of aluminum are strengthened this way.
• 2XXX (Cu added)
• 6XXX (Mg and Si added)
• 7XXX (Zn, Mg, and Cu added)
• These alloys can be solutionized at high temperature, quenched,
and aged.
Heat-Treating Alloys

• T4 temper is natural aging at room temperature.
• T6 temper is artificial aging at elevated temperature.
• Many 7XXX alloys use other temper cycles developed for
aerospace applications.
• Artificial-aging temperatures selected so cycle is hour or more
• Five minutes more or less has no effect, but overnight aging usually
leads to overaged part.
• Overaged strength drops toward annealed levels (O temper).
Heat-Treating Tempers

• Some alloys are purposely overaged to T8 condition.
• Strength is almost as great as T6.
• Corrosion resistance is better.
• Some aerospace alloys have precisely defined aging and overaging
procedures.
• These must be carefully followed to achieve desired microstructure
and performance.
Overaging for Corrosion Resistance

• Automobile hoods, decks, and fenders
• Alloy AA6009 (UNS A96009) uses Mg and Si additions for strength.
• Automobiles need dent resistance.
• Parts are formed in T4 condition.
• During paint baking, dent resistance increases.
Applications for Strengthened Aluminum

• Aircraft rivets
• Need ductility for heading during installation,
then need high strength
• Aircraft rivets of AA2117 (UNS A92117) alloy
are solutionized and quenched directly into a
freezer.
• If held at –40°F (–40°C) until used, they
remain soft and ductile.
• After installation, they harden to full strength in
a few days.
Applications for Strengthened Aluminum
(cont.)
Evgenii Nadein/Shutterstock.com

• Canoes must have light weight.
• Aluminum canoes are made from
AA6010 (UNS A96010).
• This forms sheet metal in T4 condition.
• After forming, canoes are artificially
aged to T6 properties.
• Yield strength doubles.
Applications: Canoes
LesPalenik/Shutterstock.com

• Fluidized bed furnaces have several advantages.
• They can raise parts to soak temperature very quickly.
• They can easily hold parts at controlled temperatures.
• Aluminum parts can reach temperature in under two minutes.
• Compare this to 30 or more minutes required for air furnaces.
Advanced Equipment for Improved Heat
Treatment

• Casting alloys can be precipitation hardened like wrought alloys.
• AA2XX.0, AA6XX.0, and AA7XX.0, as well as some AA3XX.0 alloys
• Parts are solutionized near 950°F (510°C), then quenched.
• T4 temper ages at room temperature.
• T6 condition is artificially aged near 350°F (175°C).
Heat Treatment of Aluminum Castings

• Cast parts have more microsegregation.
• Interdendritic regions with higher alloy concentration have lower
melting temperatures.
• Sand-cast parts must be heated slowly to solutionizing temperature.
• This allows alloys to diffuse uniformly and avoid melting.
• Partial melting (liquation) produces scrap.
Cast Aluminum and Partial Melting

• Temper is as important as alloy to
indicate tensile properties.
• Example of AA3003 (UNS A93003)
in different tempers
• H18 (fully cold-worked): very
strong, low ductility
• O (annealed): very low strength,
very high ductility
Properties of Aluminum Alloys

• Combination of properties can be produced
using roll bonding.
• Aircraft skin sheet requires high strength-to-
weight ratio and superior corrosion resistance.
• Roll bonding produces Alclad AA2024 for this
application.
• Has thin surface layer of AA7072 (UNS A97072,
Al + Zn)
• Core is AA2024 (UNS A92024, Al + Cu).
Combining Properties for Superior
Products—Alclad 2024
Ivan Cholakov/Shutterstock.com

• Aluminum can be arc welded, brazed,
or spot welded to other aluminum
parts.
• Surface must be protected from air
while hot.
• Under special conditions, aluminum
can be bonded to incompatible
metals (such as copper).
Joining Aluminum
Robert Pernell/Shutterstock.com

• Gas tungsten arc welding (GTAW) and gas metal arc welding
(GMAW) are preferred methods.
• Non-heat-treated aluminum alloys can be welded easily by trained
welders.
Joining Aluminum by Welding

• Welding eliminates strengthening effects of heat treatment in weld
area and heat-affected zone (HAZ).
• In HAZ, metal will be overaged.
• This reduces strength to annealed condition.
• Never weld or braze precipitation hardened alloys.
• Unless design expressly plans for it
Welding Heat-Treated Aluminum
Practical Metallurgy

• Automobile hoods are made by spot welding an outside layer to an
inner panel.
• Spot welding aluminum requires higher current but shorter time than
for steel.
• Fatigue life is greatly increased by combination of spot weld and
adhesive, called a spot bond.
• Apply adhesive just before electrodes clamp two sides together.
• This pushes adhesive aside to make spot welds.
Spot Welding—Automotive Hoods and
Decks

• Some frame rails of truck trailers have a warning label that says
“Caution—Do Not Weld.”
• Usually found on aerospace alloy aluminum frame rails
• These have been strengthened by precipitation hardening.
• If you see a truck trailer like this, do not weld it.
Caution—Do Not Weld
Safety Note

• Aluminum cannot be welded to copper using arc welding.
• These metals form brittle intermetallic compounds.
• Joints literally fall apart as they cool.
• But copper wire in transformers must connect electrically to
aluminum high-voltage lines.
• Mechanical aluminum-to-copper cable connections must be monitored
to avoid corrosion and overheating.
• Another solution is to flash weld them together.
Flash Welding Bus Bar Connectors

• For flash welding, a bar of copper is held one-half inch (1.2 cm)
from an aluminum bus bar of same cross section.
• An electric arc struck between them melts both faces.
• Current is turned off, and pieces are slammed together.
• Liquid metal is forced out of joint.
• Thin band of copper-aluminum intermetallic compounds remains.
• As long as joined bars never heat up, bond will last decades.
• If heated too much, intermetallic layer grows and causes failure.
Joining Copper and Aluminum by Flash
Welding

• Brazing is frequently used for joining aluminum parts.
• Braze joints tend to form smooth, fatigue-resistant joints.
• Requires flux or vacuum shielding to protect liquid aluminum
Brazing Aluminum
Jay Warner

• Consistent brazing requires an alert, experienced operator.
• All flux-brazed parts must be thoroughly rinsed in water to remove
corrosive flux.
• Brazing sheet made by roll bonding lower-melting-temperature
braze alloy onto higher-melting-temperature core.
Brazing Aluminum (cont.)

• Parts are formed, cleaned, and fitted together.
• Assembly is heated one of three ways.
• Dipped into liquid flux
• Heated in air furnace with applied flux
• Heated in vacuum furnace
• At temperature, cladding melts and fills space
between parts, making a leak-tight container
with smooth fillets.
Steps to Brazing
Goodheart-Willcox Publisher/Jay Warner

• Filler must be heated to melting point, yet core will lose too much
strength if overheated.
• Brazing temperature must be held within narrow range, such as ±20°F
(±11°C), for example, to not melt core.
• Very difficult to hold this range in furnaces
• Vacuum furnace brazing includes magnesium in the cladding to
remove any oxygen from vacuum chamber.
Brazing Requires Close Control of
Temperature

• Aluminum is used for mobile heat exchangers.
• Air conditioner evaporators, condensers, and radiators
• It conducts heat very well and has a low density.
• Components can easily be brazed into a single, leak-tight unit.
Aluminum Heat Exchangers
Practical Metallurgy

• Aluminum is difficult to join to other metal components.
• Mechanical fasteners risk concentrating stresses in small areas.
• Adhesive bonding is consistently reliable, if assembly operators can
prepare surfaces.
• Alcoa recently developed a pretreatment for adhesive bonding.
• It is applied before sheet aluminum is shipped.
Adhesive Bonding

• The flux used for brazing and welding contains up to 3.5% soluble
fluoride.
• Wastewater with dissolved fluoride severely impacts environment and
groundwater.
• Producers are under pressure to reduce or eliminate fluoride emissions.
• Shifting to non-water-soluble flux and flux-free vacuum brazing are two
ways to do this.
Reducing Fluoride Emissions

• Aluminum is easily machined with sharp tools and
adequate cooling.
• Most aluminum alloys with O and H12 tempers form
well.
• AA5XXX alloys are often specified for deep-drawing and
forming.
• AA6XXX alloys are specified for exterior parts.
• They do not develop stretcher-strain marks during forming.
• Rain gutters from AA3003-H14 strengthen during
forming.
Finish Processing of Aluminum
Jay Warner

• Aluminum can be anodized to provide a
strong oxide surface.
• Its corrosion resistance makes an excellent
exterior finish.
• Anodizing has been automated for a long
time.
• It requires very careful control of process
variables.
• Dip times, bath temperature, electric current
density, solution chemistry
Anodizing
Ekaterina Kupeeva/iStock

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