WL 112 Ch15 ch15 presentation

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Metallurgy
Fundamentals
Ferrous and Nonferrous

Introduction to
Nonferrous Metals
Chapter 15

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.
• Describe the common atomic cell structures in different metals.
• Summarize the effects of hot-working on nonferrous metals.
• Summarize the effects of cold-working on nonferrous metals.
• Describe three ways to strengthen a nonferrous alloy.
Learning Objectives

• Recognize how precipitation hardening increases the strength of
nonferrous alloys.
• Describe how galvanic corrosion affects nonferrous metals.
• Identify the basic processing methods used for nonferrous metals.
• Explain how different processing methods of nonferrous metals can
improve cast properties.
Learning Objectives

• UNS numbering system defines
composition of all commercial alloys.
• This includes ferrous alloys previously
covered and nonferrous metals.
UNS Numbering System
Goodheart-Willcox Publisher

• Applications of nonferrous metals exist because each nonferrous
metal offers different properties.
• Different metals are better suited for
certain applications.
• Similar to ferrous metals, nonferrous
metals develop physical properties
based on their atomic structure,
composition, and microstructure.
Nonferrous Metals

• Four defining properties of metals (from Chapter 4):
• Electrical conductivity
• Thermal conductivity
• Formability
• Reflectivity
• Properties are directly related to way electrons behave.
• Atoms develop crystals with precise order.
Atomic Structures in Metal Drive Unique
Properties

• Unit cell is smallest repeating structure in a crystal.
• Each atom lines up to its nearest neighbors.
• Pattern is repeated for millions of
atoms in every direction.
• As an example of size, 1 million copper
atoms along an edge of a row of unit
cells is 0.316 mm (0.0124″) long.
Unit Cells

• Pure iron is body-centered cubic (bcc) or face-centered cubic (fcc).
• Most nonferrous metals have body-centered cubic (bcc), face-
centered cubic (fcc), hexagonal close-packed (hcp), or body-
centered tetragonal (bct) unit cells.
Types of Unit Cells

• A bct unit cell resembles a bcc unit cell.
• But length in one direction is different than two other directions.
• A few metals have more complex unit cells.
Types of Unit Cells (cont.)

• Fcc metals generally have higher conductivity.
• Silver, copper, and gold (all fcc) have highest conductivity.
• Beryllium, cobalt, magnesium, and zinc form hcp unit cells.
• Drastically changes dislocation motion and ductility
• Tin has bct structure.
• A few metals have different unit cells.
• This includes bismuth, uranium, and polonium.
Crystal Structures of Nonferrous Metals

• When metal deforms, atoms in a crystal slide past one another,
forming dislocations.
• As slip continues, dislocation tangles build up.
• Force needed to move dislocations increases, making metal stronger.
• Fcc metals have more slip planes, hence greater ductility.
• Ductility of gold and silver is higher than that of bcc iron.
• Metals with hcp structure have fewer slip planes.
• They tend to be less ductile.
Slip Planes and Dislocation Tangles

• Recrystallization happens with nonferrous metals,
too.
• Recrystallization temperature varies for each
metal.
• Metals recrystallize at about 55% of their melting
temperature on kelvin temperature scale.
• For example, tin can recrystallize at room
temperature, which is 58% of its melting point.
Removing Tangles—Recrystallization

• Laboratory-purity metals recrystallize at
lower temperatures.
• Metals alloyed for applications near
melting point contain precipitates.
• Precipitates are compounds that
separate from solution upon cooling
through a phase change.
• They force recrystallization at higher
temperatures.
Recrystallization Temperatures for
Metals

• Alloys are processed to achieve microstructures with desirable
properties.
• During fabrication, ductility and formability are required.
• For service, high strength is often more important than ductility.
• Alloys may need processing to improve a different key property.
• Electrical conductivity
• Toughness
• Polished finish
Developing Desirable Properties by
Working Metal

• Hot work is deformation while hot enough to recrystallize.
• When metal is hot-worked at 60%–75% of its melting-point
temperature, dislocation tangles disappear as fast as created.
Improving Metal Properties by Hot Work

• Hot work disrupts large grains and precipitates.
• Microstructures are more uniform, with finer grains and higher
strength.
• Hot-worked metals are tougher and more ductile than cast ingots.
Improving Metal Properties by Hot Work
(cont.)

• When metal is deformed and dislocation tangles remain, this is cold
work.
• This occurs at temperatures below 50% of melting point on the
kelvin temperature scale.
• Dislocation tangles develop and increase strength and reduce
ductility.
Improving Metal Properties by Cold Work

• Deformation between hot and cold work temperatures is called
warm work.
• Tangles form.
• Only the most severe tangles recrystallize.
• Change in microstructure is called recovery.
• Warm-worked metal has some ductility and slightly higher strength
than recrystallized metal.
Improving Metal Structure by “Warm
Work”

• Annealing metals is a thermal process.
• Restoring ductility after cold-working requires annealing at 55% to
65% of the metal’s melting temperature.
• Metal recrystallizes in a few minutes at temperature.
• Forms new, strain-free, “clean” grains
Restoring Ductility by Annealing

• Heating slowly to soak temperature produces larger grains.
• Heating quickly produces finer grain size.
• Higher yield strength and better ductility
• Metal in large batch ovens may require hours to reach temperature,
as opposed to minutes in a small oven.
• Production routing sheets must state which oven to use and the
proper annealing temperature.
Different Process Sequences May
Produce Different Microstructures

• Both annealing procedures
start and finish with same
appearance.
• Final annealing in procedure B
is likely to result in larger
recrystallized grains.
• Lower strength and ductility
results.
Two Annealing Procedures: Two
Different Microstructures

• A degraded oven heating element or seizing of a belt drive in a
continuous-feed oven can affect desired results.
• This changes annealing temperature or time.
• This changes resulting microstructure and product performance.
Annealing Troubleshooting
Practical Metallurgy

• Nonferrous metals can be strengthened by cold work.
• Some alloys increase this effect.
• Certain alloy additions form large precipitates that increase yield
strength even at hot-working temperatures.
• Some nonferrous alloys can be heat-treated to dramatically
increase strength and hardness.
Strengthening through Alloying

• There is one significant difference in stress-
strain behavior of nonferrous metals,
compared to steel.
• Plain carbon steels have clear break in
stress-strain curve when reaching yield point.
• Most nonferrous metals gradually change
from elastic to plastic regions.
• Yield strength for nonferrous metals is
defined as stress where stress-strain curve
crosses a 0.2% offset line.
Measurement of Yield Strength in
Nonferrous Metals

• Cold work (cold-rolling or cold forging) alters properties by
developing dislocation tangles.
• Increases strength and hardness; reduces ductility
• Cold-worked sheet metal is more dent- and wrinkle-resistant than
annealed sheet.
• Sheet metal is usually offered for sale with a cold-roll strengthening
option.
Strengthening Alloys through Cold Work

• Some alloys are strengthened by adding alloy elements that do not
change crystal structure.
• Called a solid solution alloy
• Alloy atom size is different.
• Stresses develop around them.
• Dislocation motion is more difficult.
• Strength increases.
Strengthening by Solid Solution Alloying

• Grains quickly slide past one another at high temperatures.
• Metal deforms at low stress.
• At warm-work temperatures, metal deforms in longer times.
• Creep occurs at stresses less than yield strength.
• To obtain high-temperature strength and reduce creep requires
adding certain element.
• Element must form stable precipitate particles at high temperatures.
Strengthening by Large Precipitates

• Many nonferrous alloys can be precipitation hardened.
• Copper
• Aluminum
• Nickel
• Titanium
• Copper alloy UNS C17200 (CDA 172) demonstrates the process.
• It is copper alloyed with 1.7% beryllium.
Strengthening through Heat Treatment—
Precipitation Hardening

• C17200 alloy strip arrives at fabrication plant
in position A.
• Two-phase region contains large CuBe
particles in copper matrix.
• Completely recrystallized by final anneal
from production plant
• Not strong but ductile
Cu-Be Phase Diagram

• After forming from sheet, parts are heated to position B.
• CuBe particles dissolve into copper matrix.
• Called solutionizing temperature, because alloys are single solution.
• Metal may be called solutionized.
Cu-Be Phase Diagram (cont.)

• After solutionizing, parts are removed from furnace
and quenched to position C.
• Usually water quenched, but some alloys are cooled
other ways.
• Temperature drops so fast, precipitate particles
cannot form.
• Large number of extremely small “pre-precipitate”
regions develop.
• As-quenched metals have good ductility and slightly
greater strength than fully annealed material.
Formation of Second-Phase Precipitates

• With precipitation hardening of nonferrous alloys, heat-treat
procedure is similar for each alloy:
1. Workpiece is heated to a high temperature until second element is
in solution in a single phase.
2. Workpiece is rapidly quenched to a low temperature. The second
element remains in solution.
3. Workpiece is aged at a moderate temperature. Small, fine
precipitates involving the second element form uniformly throughout
the workpiece.
Procedure: Precipitation Hardening

• When Cu-1.7% Be alloy is first quenched, no particles can be seen.
• Tiny pre-precipitate regions of CuBe soon form.
• Lattice of CuBe precipitates almost lines up with copper crystals.
• Stressed regions surround each precipitate, as precipitates align at
particle-copper matrix interface.
• Particles are called coherent precipitates.
• Strength is greatly increased by this room-temperature process
called natural aging.
Growing Precipitates: Natural Aging

• After quench, copper-beryllium alloy is
heated to position D.
• Beryllium atoms diffuse from copper matrix
to new CuBe particles.
• CuBe precipitates grow in minutes.
• Sharply increases strength but reduces
ductility
• Called artificial aging (elevated-temperature
aging)
Artificial Aging

• Higher temperatures allow shorter aging time.
• Process requires very close control of time and temperature.
Artificial Aging (cont.)

• Furnace time for artificial aging can be few minutes to an hour.
• Depends on soak temperature, size of part, and alloy elements
Furnace Time for Artificial Aging

• If aging time continues, second-phase particles grow too large.
• Stresses surrounding particles relax as strength and hardness drop.
• This is called overaging (shown for an aluminum-copper alloy).
• Some overaged alloys resist corrosion better, making this desirable.
Overaging

• This ferrous alloy contains 1% aluminum to strengthen it.
• Its heat-treat cycle:
• High-temperature solutionizing step is 1800°F (980°C).
• Quench in oil.
• Artificial age at 1200°F to 1400°F (650°C to 760°C) for one hour.
• In quenched condition, metal has high formability and machinability.
• After aging, it has much higher strength.
Age Hardening UNS S17700 (17-7PH)
Stainless Steel

• Like ferrous metals, nonferrous metals must be separated from their
ores and refined.
• This is accomplished using chemical or electrical reactions.
• Reactions of certain nonferrous metals (like oxidation rate) can be
put to good use.
Reactions of Nonferrous Metals during
Refining and Use

• Metals are obtained by mining ores or by extraction from mineral-
rich water called brine.
• Refined by a variety of chemical and electrolytic methods
• In oxide form, some ores can be reduced using carbon.
• Produces metal and carbon dioxide (CO2)
• Similar to reducing iron ore
Extracting and Refining Nonferrous
Metals

• Some ores are ground to a fine powder, dissolved in a chemical
solution, and refined electrolytically.
• Uses electric current to reduce metal oxides to metal
• Some metal ores are found as sulfide compounds.
• Converted to metal oxides plus sulfur dioxide (SO2) by roasting in air
• Sulfur dioxide is converted into sulfuric acid (H2SO4) and sold.
• Sometimes sulfur dioxide escapes into the air.
Extracting and Refining in Other Ways

• Large mining activities can disrupt landscape for miles around.
• Leaks from ore-roasting ovens put sulfur dioxide (SO2) into atmosphere.
• SO2 forms acid fog and rain, causing serious environmental damage.
• Gas masks, fume hood ventilators, and exhaust scrubbing equipment are
important for safety.
• Almost any mining operation disrupts terrain and water.
• These things must be considered when planning and operating mines.
• Most mines today do not generate pollutants as in past.
Mining Effects
Sustainable Metallurgy

• Suppose two different metals are electrically connected.
• If placed in a conductive environment, a voltage occurs.
• This drives a current of electrons moving from one metal to another.
• One metal piece will corrode, and electron flow (current) will reduce
corrosion in the other metal.
• More rapidly corroding metal undergoes galvanic corrosion.
Corrosion of Nonferrous Alloys

• Zinc on galvanized steel corrodes and
protects steel underneath from oxidation.
• Zinc is very electronegative.
• Ease of processing makes zinc excellent
choice for protecting steel.
• The more electronegative a metal, the
better it will protect.
• Greater differences in electronegativity
have a greater effect.
Electronegativity of Metals

• Fabrication methods for nonferrous parts are similar to those used
for steel.
• Casting, bulk deformation, forming, heat-treating, joining, finishing
• Equipment is similar to that for steels, with two differences:
• Melting and processing temperatures are lower for many nonferrous
metals.
• Some refined nonferrous metals are much more reactive than steel
and must be carefully protected from exposure to air.
Processing Used in Nonferrous
Metallurgy

• A vacuum chamber is never completely void of air.
• Pressure in chamber depends on how well air is
pumped out.
• Industrial vacuum chambers report pressure in torr.
• One standard atmosphere pressure equals 760 torr.
• Vacuum chamber consists of leak-free container,
well-sealed doors, electric heating elements, and
pumps to remove gases.
Vacuum Chambers and Pumps (Part 1)
Solar Atmospheres

• For some operations, oxidation/discoloring are
acceptable.
• A mechanical roughing pump moves enough gas out.
• This achieves a pressure of approximately 10-3 torr.
• For processing more reactive metals, two pumps are
used.
• Oil diffusion pumps, in sequence with roughing
pumps, reduce pressure below 10–5 torr.

• Pressure below 10–5 torr is high vacuum.
• Vacuum systems require very good seals at all openings.
• Neoprene or annealed copper O-rings are used.
• Pumps are designed to handle severe outgassing as parts and
materials are heated in vacuum furnaces.
• Alternatively, heating rate must be reduced so pumps can handle
outgassing.

• Sand, clay slurry, and permanent steel molds commonly used
• Die casting is used for alloys that melt below 1200°F (650°C).
• Outside of US, it is referred to as pressure die casting.
Casting
Mr.1/Shutterstock.com

• Die casting process:
• Liquid metal is forced into a closed steel die.
• It solidifies into very precise shapes.
• Die is opened, and ejector pins push casting out of die.
• Part falls into a bin or is captured by a robot.
Die Casting Process

• Steel dies require considerable machining and heat-treating.
• Only large production runs are made by die casting.
• Dies are saved by casting firms for repeat orders.
• To produce uniform castings, several variables are monitored:
• Melt temperature, die temperature, plunger speed, ram force
• Operators must be alert for other potential problems.
• Long hold times increase porosity.
• Open shop windows create drafts.
Die Casting

• In cold-chamber die casting, liquid
metal is poured into a shot chamber
(shot sleeve).
• Either manually or by machine
• Plunger forces liquid metal into a die,
where it quickly freezes.
• Aluminum die casting is usually done
using cold chambers.
Cold-Chamber Die Casting

• A tube is immersed in liquid metal,
and a vertical plunger forces liquid
up through a “gooseneck” (feeding
spout).
Hot-Chamber Die Casting

• Metal enters die cavity without being exposed to air.
• No oxides or flux enter die.
• Parts have higher integrity.
• Only alloys that do not erode steel are used.
• Plunger and gooseneck are continuously exposed to liquid metal.
• Magnesium and zinc alloys work well.
Hot-Chamber Die Casting (cont.)

• Due to erosion caused by liquid metal, dies must be reworked
occasionally to maintain dimensions.
• Steel alloys for molds are selected to minimize heat checking (the
formation of surface cracks due to repeated thermal cycling).
• If melt temperature or ram velocity is too low, liquid metal will not fill
the part (called a short shot).
• If ram pressure is too high or dies are worn, flash forms between die
halves and is usually removed by manual grinding.
Problems with Hot-Chamber Die Casting

• Pores form in most nonferrous alloys during casting at atmospheric
pressure.
• Due to shrinkage and gases coming out of solution during solidification
• Process called hot isostatic pressing (HIP) can close and heal pores.
• Casting compressed in isostatic chamber at high pressure and temperature
• Isostatic means that pressure is applied equally from all directions.
• HIP improves elongation and yield, tensile, and fatigue strength.
• Aerospace and critical-to-safety castings often require HIP.
Improving Cast Properties by Hot
Isostatic Pressing (HIP)

• Process injects a slurry of partly solidified metal into a die.
• Resulting parts have improved properties.
• Minimal oxides
• Less microsegregation
• Easier to heat-treat to high strength
• More uniform properties
• Lower casting temperatures reduce wear on dies.
Semisolid Metal (SSM) Casting

• Small spheroids form in a melted alloy if it is stirred while cooling.
• If not stirred, dendrites interlock, acting like a weak solid (while still
liquid).
Dendrites

• A liquid-solid mixture behaves like a liquid as long as it is stirred.
• This is called thixotropic behavior.
• Prepared, heated material can be handled with tongs.
• Surface tension keeps solid globules together.
• When ram forces it into die cavity, it becomes fluid and easily flows.
Changing Dendrites to Spherical
Particles

• Preparing liquid-solid condition can be done at point of injection into
die.
• Casting alloy below fully liquid temperature reduces die wear.
Thixotropic Casting

• Microstructure is more uniform than casting a liquid.
• This improves properties.
• Temperatures and stirring rates must be closely controlled by
knowledgeable and alert operators.
Thixotropic Microstructure

• Rolling, forging, extrusion, and drawing of nonferrous metals are
similar to steel production.
• Ingot processing requires hot-working temperatures.
• Metals that react with air must be protected by inert gas, a vacuum,
or another method.
Bulk Deformation Processing of
Nonferrous Metals

• Hot-rolling nonferrous metals much like hot-rolling steel.
• Many nonferrous alloys forged to obtain improved properties
• Many nonferrous metals can be extruded into long pieces of
complex cross sections and hollow shapes.
• Tubes with internal ribs can only be made by extrusion.
• Some parts can be made by back extrusion.
Rolling, Forging, and Extrusion

Extruded Tube and Back Extrusion
Jay Warner; Goodheart-Willcox Publisher

• Nonferrous alloys with good ductility
can be drawn, or pulled, into round or
oval shapes.
• Like steel, amount of reduction in
single draw is limited by yield
strength of workpiece.
Drawing

• Parts are made from powdered nonferrous metals by compacting on
same equipment used for steel.
• Metals like brass are less reactive than iron powder.
• Sintering uses same furnaces as steel.
• Sintering reactive metals often requires special furnaces.
• Aluminum often requires this.
• Titanium always requires this.
PM Part Production from Powdered
Nonferrous Metal

• It bears repeating: Reactive metal powders must be stored safely
and handled with caution.
• Powdered metals can cause lung damage and allergic reactions.
• They also present a fire and explosion hazard.
Metal Powders
Safety Note

• Most nonferrous metals are easily formed, shaped, and cut.
• Stamping presses need only small changes in dies to use different
alloys.
• Several things are determined by the formability of the workpiece
metal.
• Minimum press size, minimum die corner radii, and maximum drawing
depth of part
Forming, Shaping, and Cutting

• Most nonferrous metal heat-treating is done by solutionizing,
quenching, and aging.
• After forming parts, they are heat-treated.
• Heated in ovens and quenched in water, oil, or air
• Finally, aged to develop strength through precipitate second-phase
particles
• Controlled atmospheres minimize oxidation if necessary.
Heat Treatment Processing

• Partial melting, or liquation, can occur if alloy is processed incorrectly
during heat treatment.
• During casting, alloy elements concentrate between freezing dendrites.
• These interdendritic regions are pockets that melt at lower temperatures.
• Problem is worse in sand castings (slow solidification).
• Reheating castings slowly reduces this problem.
• Concentrated elements diffuse and spread through part.
• More uniform composition means properties are more uniform.
Avoiding Partial Melting during Heat
Treatment

• Some alloys have narrow solutionizing temperature ranges.
• These alloys need very uniform-temperature furnaces.
• Frequent furnace calibrations are usually required.
• Fluidized bed furnaces offer one method to heat-treat alloys with
narrow temperature ranges.
• Tank partly filled with dry sand has hot gas pumped from bottom,
creating quicksand effect that produces very uniform temperatures.
Using Fluidized Bed Furnaces

• Open baskets holding small parts slide easily into bubbling sand.
• Upon removal, parts are dry and sand shakes off.
• Heating time is much shorter than in air furnaces.
• Tighter process controls mean technicians and operators must
watch production closely.
Process Control with Fluidized Bed
Furnace

• Joining forms a metallurgical bond between
two workpieces.
• To make bond, surface oxide on workpieces
must be disrupted.
• A bond can be formed with or without liquid
metal at joint.
• Roll bonding hot-rolls two metal plates
together.
• Typically metal with different properties on
each side of sheet
Joining Nonferrous Metals
vlaru/Shutterstock.com

• Parent and filler metals must be metallurgically compatible.
• Compatible alloys do not form damaging intermetallic compounds.
• Fusion-welded parent alloys usually have the same major metal.
• Most nonferrous metals must be shielded from oxygen.
• Shielded compatible metals can be fusion welded many ways.
• Electric arc or gas torch welding, resistance welding, friction welding
• Procedures are done with or without filler.
Fusion Welding: Joining by Melting
Parent Metals

• Performed above 815°F (435°C)
• Parent metal does not melt.
• Filler alloy melts and penetrates parent metal
oxide.
• Surface tension pulls liquid filler into joint area.
• Filler metal penetrates crevices not visible from
outside.
• It forms a smooth, round fillet.
• Flux is used to protect filler and disrupt oxide
layer.
Brazing
Jay Warner

• Brazing can be done manually by skilled technicians.
• Radiators and heat exchangers require many brazed joints.
• Best done with braze-clad sheet (brazing sheet)
• Made by roll-bonding slabs of braze filler alloy onto core ingot.
• Sheet is formed, assembled, and stacked into steel fixtures.
• These are placed in an oven or dipped into a tank of hot liquid flux.
• They are heated so cladding melts but core does not.
• Many joints can be made in a heat exchanger in one furnace cycle.
Brazing Methods

• All soldering involves filler metal that melts below 815°F (435°C).
• Parent metal does not melt.
• Almost all soldering requires a flux active at soldering temperature.
• Surface tension pulls liquid filler into a smooth round fillet.
• Just like brazing
Soldering

• Lead is traditionally a major component of solder filler alloys.
• Great effort in last 35 years to minimize lead in solder alloys
• This has reduced lead in the environment and the exposure to lead
in several job fields.
• Plumbers and other workers who use solder
Get the Lead Out
Sustainable Metallurgy

• Very hard alloys can be cut using electric discharge machining
(EDM).
• Workpiece is placed in nonconductive fluid.
• An electrode is brought close while high voltage is applied.
• When very close, an electric spark jumps between them.
• Each spark removes a small amount of metal.
• Complex shapes can be made in minutes.
Machining

• Both nickel and chromium are plated to
protect steel or brass from corroding.
• One way to obtain desirable finishes is to
chemically treat surfaces.
• Some nonferrous alloys can be anodized.
• This forms a uniform, adherent, hard oxide on
a metal surface.
• It protects parts from further corrosion and
scratches.
Plating: Providing a Shiny, Corrosion-
Resistant Surface
Ali_Cobanoglu/Shutterstock.com

• Some applications must use two or more
metals to make a useful product.
• Thermostat control switches are usually a
blade of two roll-bonded metals.
• Must have different coefficients of
expansion
• Copper, nickel, and gold are used to make
removable electrical contacts in low-
voltage circuits.
• Chipped credit cards, for example
Applications That Use Multiple Metals
nobeastofierce/Shutterstock.com

• Some metals are biologically hazardous.
• Operators and users must be alert for such hazards.
• Working with beryllium alloys puts beryllium oxide (BeO) dust into the air,
which can cause berylliosis (sapping lung capacity).
• The negative long-term effects of lead exposure are well known.
• Cadmium is no longer used to plate fasteners due to its toxicity.
• Spent chrome plating solutions contain hexavalent chrome, a major
biohazard, and they must be handled carefully.
Biological Hazards
Safety Note

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