Non Ferrous Alloys

7/21/2019 Non Ferrous Alloys

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Non-Ferrous Alloys

Prof. P. G. Mukunda

IIT Kharagpur.

1.0 Aluminum alloysAluminum possesses a combination of properties which make it an extremely useful

engineering material. Aluminum has a low density (2.70 g/cm3! making it particularly

useful for transportation manufactured products. Aluminum also has good corrosion

resistance in most natural en"ironments due to the tenacious oxide film which forms on

its surface. Aluminum is nontoxic and used extensi"ely for food containers and

packaging. #he good electrical properties of aluminum make it suitable for many

applications in the electrical industry. Aluminum is used extensi"ely in the form of alloys.

Aluminum alloys are strengthened by precipitation$strengthening mechanism. %o it&s

important to discuss first precipitation strengthening mechanism.

1.1 lassifi!a"ion of #rough" aluminum alloys

Aluminum alloys are produced in the wrought form (i.e.! sheet! plate! extrusions!

rod! and wire are classified according to the ma'or alloying elements they contain. A

four$digit numerical designation is used to identify aluminum wrought alloys. #he first

digit indicates the alloy group which contains specific alloying elements. #he last two

digits identify the aluminum alloy or indicate the aluminum purity. #he second digit

indicates modification of the original alloy or impurity limits.

rought aluminum alloys can con"eniently be di"ided into two groups) non$heat$

treatable and heat$treatable alloys. *on$heat$treatable aluminum alloys cannot be

precipitation$strengthened but can only be cold$worked to increase their strength. #he

three main groups of non$heat$treatable wrought aluminum alloys are the +xxx! 3xxx! and

,xxx groups. #able + lists the chemical composition! typical mechanical properties! and

applications for some selected industrially important wrought aluminum alloys.

1.1.1 Non-hea"-"rea"a$le #rough" aluminum alloys

1xxx alloys. #hese alloys ha"e a minimum of --.0 aluminum with iron and silicon

being the ma'or impurities (alloying elements. An addition of 0.+2 copper is added for

extra strength. #he ++00 alloy has a tensile strength of about -0a in the annealed

condition and is sued mainly for sheet metal work applications.



3xxx alloys. anganese is the principal alloying element of this group and strengthens

aluminum mainly be solid$solution strengthening. #he most important alloy of this group

is 3003! which is essentially an ++00 alloy with the addition of about +.2, manganese.

#he 3003 alloy has a tensile strength of about ++0a in the annealed condition and is

used as a general purpose alloy where good workability is re1uired.

5xxx alloys. agnesium is the principal alloying element of this group and is added for

solid$solution strengthening in amounts up to about ,. ne of the most industrially

important alloys of this group is ,0,2! which contains about 2., magnesium (g and

0.2 chromium (r. 4n the annealed condition alloy ,0,2 has a tensile strength of about

+-3a. #his alloy is also used for sheet metal work! particularly for bus! truck! and

marine applications.

1.1.% &ea"-"rea"a$le-#rough" aluminum alloys

%ome aluminum alloys can be precipitation$strengthened by heat treatment. 5eat$

treatable wrought aluminum alloys of the 2xxx! 6xxx! and 7xxx groups are all

precipitation hardened. #able + lists the chemical compositions! typical mechanical

properties! and applications of some of the industrially important wrought heat$treatable

alloys.

2xxx alloys. #he principal alloying element of this group is copper! but magnesium is also

added to most of these alloys. %mall amounts of other elements are also added. ne of the

most important alloys of this group is 2028! which contains about 8., copper (u!

+., g! and 0.6 n. #his alloy is strengthened mainly by solid$solution and

precipitation strengthening. An intermetallic compound of the approximate composition

of Al2ug is the main strengthening precipitate. Alloy 2028 in the #6 condition has a

tensile strength of about 882a and is used! for example! for aircraft structurals.

6xxx alloys. #he principal alloying elements for the 6xxx group are magnesium and

silicon which combine together to form an intermetallic compound! g2%i! which in

precipitate form strengthens this group of alloys. Alloy 606+ is one of the most important

alloys of this group and has an approximate composition of +.0 g! 0.6! 0.6 %i!

0.3 u! and 0.2 r. #his alloy in the #6 heat$treated condition has a tensile strength

of about 2-0 a and is used for general$purpose structurals.



7xxx alloys. #he principal alloying elements for the 7xxx group of aluminum alloys are

9inc! magnesium! and copper. :inc and magnesium combine to form an intermetallic

compound! g:n2! which is the basic precipitate that strengthens these alloys when they

are heat$treated. #he relati"ely high solubility of 9inc and magnesium in aluminum makes

it possible to create a high density of precipitates and hence to produce "ery great

increases in strength. Alloy 707, is one of the most important alloys of this group and has

an approximate composition of ,.6 :n! 2., g! +.6 u! and 0.2, r. Alloy 707,

when heat$treated to the #6 temper! has a tensile strength of about ,08a and is used

mainly for aircraft structures.

1.% Pre!ipi"a"ion s"reng"hening of a generali'ed $inary alloy

#he precipitation$strengthening process can be explained in a general way by

referring to the binary phase diagram of metals A and ; shown in <ig.+. 4n order for an

alloy system to be able to be precipitation$strengthened for certain alloy compositions!

there must be a terminal solid solution which has a decreasing solid solubility as the

temperature decreases. #he phase diagram of <ig.+ shows this type of decrease in solid

solubility in terminal solid solution α in going from point a to b along the indicated

sol"us.

<igure + ;inary phase diagram for two metals A and ; ha"ing a terminal solid solution



=et us now consider the precipitation strengthening of an alloy of composition x+ of the

phase diagram of <ig.+. e choose the alloy composition x+ since there is a large

decrease in the solid solubility of solid solution α in decreasing the temperature from #2

to #3. #he precipitation$strengthening process in"ol"es the following three basic steps)

+. %olution heat treatment is the first step in the precipitation$strengthening process.

%ometimes this treatment is referred to as solutioni9ing. #he alloy sample which

may be in the wrought or cast form is heated to a temperature between the sol"us

and solidus temperature and soaked there until a uniform solid$solution structure

is produced. #emperature #+ at point c of <ig.+. is selected for our alloy x+

because it lies midway between the sol"us and solidus phase boundaries of solid

solution α.

2. >uenching is the second step in the precipitation$strengthening process. #he

sample is rapidly cooled to a lower temperature! usually room temperature! and

the cooling medium is usually water at room temperature. #he structure of the

alloy sample after water 1uenching consists of a supersaturated solid solution. #he

structure of our alloy x+ after 1uenching to temperature #3 at point d of <ig.+ thus

consists of a supersaturated solid solution of the α phase.

3. Aging is the third step in the precipitation$strengthening process. Aging the

solution heat$treated and 1uenched alloy sample is necessary so that a finely

dispersed precipitate forms. #he formation of a finely dispersed precipitate in the

alloy is the ob'ecti"e of the precipitation$strengthening process. #he fine

precipitate in the alloy impedes dislocation mo"ement during deformation by

forcing the dislocations to either cut through the precipitated particles or go

around them. ;y restricting dislocation mo"ement during deformation! the alloy is

strengthened.

Aging the alloy at room temperature is called natural$aging! whereas aging at ele"atedtemperatures is called artificial aging.

1.( )e!omposi"ion produ!"s !rea"ed $y "he aging of "he supersa"ura"ed solid solu"ion

A precipitation$hardenable alloy in the supersaturated solid$solution condition is in a high

energy state! as indicated schematically by energy le"el 8 of <ig.2. #his energy state is

relati"ely unstable! and the alloy tends to seek a lower energy state by the spontaneous



decomposition of the supersaturated solid solution into metastable phases or the

e1uilibrium phase is the lowering of the energy of the system when these phases form.

hen the supersaturated solid solution of the precipitation$hardenable alloy is aged at a

relati"ely low temperature where only a small amount of acti"ation energy is a"ailable!

clusters of segregated atoms called precipitation 9ones or ? 9ones! are formed. <or the

case of our alloy A$; of <ig.+! the 9ones will be regions enriched with ; atoms in a

matrix primarily of A atoms. #he formation of these 9ones and precipitates in the

supersaturated solid$solution is indicated by the circular sketch at the lower energy le"els

of 3! 2 and + in <ig.2.

<igure 2 @ecomposition products created by the ageing of a supersaturated solid solutionof a precipitation$hardenable alloy. #he highest energy le"el is for the supersaturated

solid solution! and the lowest energy le"el is for the e1uilibrium precipitate. #he alloy can

go spontaneously from a higher energy le"el to a lower one if there is sufficient acti"ationenergy for the transformation and if the kinetic conditions are fa"ourable.

1.* Pre!ipi"a"ion s"reng"hening of an Al-*+ u alloy

#he heat$treatment se1uence for the precipitation strengthening of this alloy is)

i %olution heat treatment) the Al 8 u alloy is solutioni9ed at about ,+,

(<ig.3.

ii >uenching) the solution heat$treated alloy is rapidly cooled in water at room

temperature.

iii Aging) the alloy after solution heat treatment and 1uenching is artificially

aged in the +30 to +-0 range.



<igure 3 Aluminum rich end aluminum$copper phase diagram

1., "ru!"ures formed during "he aging of "he Al- *+ u alloy

#he general se1uence of precipitation in binary aluminum$copper alloys can be

represented by

%uper saturated solid solution ?+ 9ones ?2 9ones (θ&& phase θ& θ (uAl2

#he hardness "s. aging time cur"es for an Al$8 u alloy aged at +30 and +-0 are

shown in <ig.8. At +30! ?+ 9ones are formed and increase the hardness of the alloy

by impeding dislocation mo"ement. <urther aging at +30 creates ?2 9ones which

increase the hardness still more by making dislocation mo"ement still more difficult. A

maximum in hardness is reached with still more aging time at +30 at θ& forms. Aging

beyond the hardness peak dissol"es the ?2 9ones and coarsens the θ& phase and causes

the decrease in the hardness of the alloy. ?+ 9ones do not form during aging at +-0 in

the Al$8 u alloy since this temperature is abo"e the ?+ sol"us. ith long aging times

at +-0 the e1uilibrium θ phase forms.



<ig.8 orrelation of structures and hardness of Al$ 8 u alloy aged at +30° and +-0°

%.0 opper alloys

opper is an important engineering metal and is widely used in the unalloyed condition

as well as combined with other metals in the alloyed form. 4n the unalloyed form! copper

has an extraordinary combination of properties for industrial applications. %ome of these

are high electrical and thermal conducti"ity! good corrosion resistance! ease of

fabrication! medium tensile strength! controllable annealing properties! and general

soldering and 'oining characteristics. 5igher strengths are attained in a series of brass and

bron9e alloys which are indispensable for many engineering applications.

%.1 opper-'in! alloys /rasses

#he copper$9inc brasses consist of a series of alloys of copper with additions of

about , to 80 9inc. opper forms substitutional solid solutions with 9inc up to about

3, 9inc. #he microstructure of the single phase alpha brasses consists of an alpha solid

solution! as shown in <ig., for a 70u$ 30:n alloy (cartridge brass. #he

microstructure of the 60 u$ 80 :n brass (munt9 metal has two phases! alpha and

beta! as shown in <ig.6.#he tensile strength of some selected brasses are listed in #able 2.



<igure , icrostructure of cartridge brass (70 u$30:n in the annealed condition.

<igure 6 5ot$rolled unt9 metal sheet ( 60 u 80 :n. %tructure consists of beta

phase (dark and alpha phase (light



%.% opper-"in alloys /ron'es

opper$tin alloys! which are properly called tin bron9es but often called phosphor

bron9es! are produced by alloying about + to +0 tin with copper to form solid$solution$

strengthened alloys. rought tin bron9es are stronger than u$:n brasses! especially in

the cold$worked condition! and ha"e better corrosion resistance. u$%n casting alloys

containing up to about +6 %n are used for high$strength bearings and gear blanks.

%.( opper-$eryllium alloys

opper$beryllium alloys are produced containing between 0.6 to 2 with

additions of cobalt from 0.2 to 2.,. #hese alloys are precipitation$hardenable and can

be heat$treated and cold$worked to produce tensile strengths as high as +863 a! which

is the highest strength de"eloped in commercial copper alloys. u$;e alloys are used for

tools re1uiring high hardness and nonsparking characteristics for the chemical industry.

#he excellent corrosion resistance! fatigue properties! and strength of these alloys make

them useful for springs! gears! diaphragms! and "al"es.

(.0 Magnesium alloys

agnesium is a light metal (density B +.78 g/cm3 and competes with aluminum (density

B 2.70 g/cm3 for applications re1uiring a low$density metal. 5owe"er! magnesium and

its alloys ha"e many disad"antages which limit their widespread usage. 4t has relati"ely

low strength! poor resistance to creep! fatigue and wear. 4n addition! magnesium has the

5 crystal structure which makes deformation at room temperature difficult. n the

other hand! because of their "ery low density! magnesium alloys are used ad"antageously!

for example! for aerospace applications and material$handling e1uipment. #here are two

types of magnesium alloys) wrought alloys! mainly in the form of sheet! plate! extrusions!

and forgings! and casting alloys. ;oth types ha"e non$heat$treatable and heat$treatable

grades.

agnesium has the 5 crystal structure! and thus the cold working of magnesium

alloys can only be carried out to a limited extent. At ele"ated temperatures for

magnesium! some slip planes other than the basal planes become acti"e. #hus magnesium

alloys are usually hot$worked or warm$worked instead of being cold$worked.



Aluminum and 9inc are commonly alloyed with magnesium to form wrought magnesium

alloys. Aluminum and 9inc both increase the strength of magnesium by solid$solution

strengthening. #able 3 lists the properties! composition and application of some

magnesium based alloys.

*.0 Ti"anium alloys

#itanium has the 5 crystal structure (alpha at room temperature which

transforms to the ; (beta structure at CC3. Dlements such as aluminum and oxygen

stabili9e the α phase and increase the temperature at which the α transforms to the β

phase. ther elements such as "anadium and molybdenum stabili9e the beta phase and

lower the temperature at which β phase is stable.

#able 8 lists representati"e types of alpha! alpha$beta! and beta titanium alloys along with

their nominal chemical compositions! typical mechanical properties! and applications.

#he extensi"ely used titanium alloy is #$6Al$8E since this alloy combines high strength

with workability and low density (for titanium alloys. ;y solution heat treating and

aging! its tensile strength may reach ++73 a. #his alloys is used! for example! for

blades and disks in aircraft gas turbine engines as well as for chemical process

e1uipment.

4n the +--0s beta$stabili9ed titanium alloys ha"e become more prominent although still a

relati"ely small amount of the titanium markets. #hese alloys pro"ide higher strengths

and workability but higher densities. #he beta alloy #i$+0E$2<e$3Al has been used for

forgings in the 777 passenger aircraft.

,.0 Ni!kel alloys

*ickel is an important engineering metal mainly because of its exceptional

resistance to corrosion and high$temperature oxidation. *ickel also has the < crystal

structure which makes it highly formable.

,.1 ommer!ial ni!kel and Monel alloys

ommercially pure nickel because of its good strength and electrical conducti"ity is used

for electrical and electronics parts and because of its good corrosion resistance for food$

processing e1uipment. *ickel and copper are completely soluble in each other in the solid

state at all compositions! and so many solid$solution$strengthened alloys are made with

nickel and copper. *ickel is alloyed with about 32 copper to produce the onel 800



alloy (#able , which has a relati"ely high strength! weldability! and excellent corrosion

resistance to many en"ironments. #he 32 copper strengthens the nickel to a limited

extent and lowers its cost. #he addition of about 3 aluminum and 0.6 titanium

increases the strength of onel significantly by precipitation strengthening.

,.% Ni!kel-$ase superalloys

A whole spectrum of nickel$base superalloys ha"e been de"eloped primarily for gas

turbine parts which must be able to withstand high temperatures and high oxidi9ing

conditions and be creep$resistant. ost wrought nickel$base superalloys consist of about

,0 to 60 nickel! +, to 20 chromium! and +, to 20 cobalt. %mall amounts of

aluminum (0., to 8 and titanium (+ to 8 are added for precipitation strengthening.

#he nickel$base superalloys usually consist essentially of three main phases) + a matrix

of gamma austenite! 2 a precipitate phase of *i3Al and *i#i called gamma prime! and 3

carbide particles (due to the addition of about 0.0+ to 0.08 . the gamma prime

pro"ides high$temperature strength and stability to these alloys! and the carbides stabili9e

the grain boundaries at high temperatures.





Ta$le % Typi!al me!hani!al proper"ies and appli!a"ion of !opper alloys



Ta$le ( hemi!al !omposi"ion and "ypi!al me!hani!al proper"ies and appli!a"ions of

magnesium alloys



Ta$le * hemi!al !omposi"ion and "ypi!al me!hani!al proper"ies and appli!a"ions of

Ti"anium and Ni!kel alloys

Non Ferrous Alloys

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