Material Technology

1 J3022 Material Technology 1
CHAPTER 5 : CORROSION & NON-FERROUS METAL
5.0 What is Corrosion?
 Corrosion is defined as the destruction of a metal by chemical or
electrochemical reaction with its surrounding (environment).
 Corrosion can occur in a gaseous environment (dry corrosion) or a
wet environment (wet corrosion).
 Importance of corrosion:
1. Economic – direct or indirect losses
2. Improved safety – failure of critical component
3. Conservation of resource – wastage of metal or energy
 Corrosion falls into 2 main categories:
1. General or uniform corrosion
2. Localised corrosion
5.1 General or Uniform Corrosion
 The electrochemical reactions occur at the same rate over the
entire surface.
 This type of attack is mostly found where a metal is in contact with
an acid, a humid atmosphere or in a solution.
 Example 1:
Zn + HCl ZnCl2 + H2 (g)
Oxidation : anodic Zn Zn+2 + 2e-
Reduction : cathodic 2H+ + 2e- H2
Zn
Zn
HCl
Zn Zn

 Example 2:
 Place the piece of Zn in a solution containing copper sulphate
CuSO4 (blue solution).
 Observation: A dark deposit of Cu on Zn and fading of the blue
solution.
Zn + Cu+2 Cu + Zn+2
Oxidation : anodic Zn Zn+2 + 2e-
Reduction: cathodic Cu+2 + 2e- Cu
 Conclusion : Any reaction that can be divided into two or more
partial reactions of oxidation and reduction is called
electrochemical.
 Prevention : Proper material selection, change the environment,
Cathodic protection.
Zn
ZnHCl
Zn Zn
CuSO4

5.2 Localised Corrosion
 There are different types of localised corrosion:
1. Galvanic corrosion
2. Pitting corrosion
3. Crevice corrosion
4. Intergranular corrosion
5. Dealloying
6. Fretting corrosion
7. Cavitation corrosion
8. Erosion corrosion
9. Environmentally induced cracking
i. Hydrogen embrittlement
ii. Stress corrosion cracking (SCC)
iii. Corrosion fatigue
5.2.1 Galvanic Corrosion
 Occur when 2 different metals are electrically connected in the
same electrolyte.
 The less active (more noble) metal corrodes slower and will be
protected.
 The galvanic series will predict which metal will corrode.
 The galvanic series is similar to the “emf” but is for alloys in real
environment.

 Experimental corrosion (zinc and cuprum) :
i. A zinc electrode connected to a cuprum electrode and
immerse in an electrolyte such as salt water, acid or
alkaline
ii. The cuprum acts as cathodic and the zinc as anodic
iii. Zinc will be corrode caused by the electrochemical
corrosion
iv. Time to time the zinc will continue to corrode and
became embrittle, fragile and weakening.
 Factors affecting the severity galvanic corrosion are :
1. Size of exposed areas of the anodic metal relative to that of
cathodic metal.
i. Smaller cathode relative to anode will cause small
increase in corrosion of anode.
ii. Smaller anode will suffer severe corrosion.

5.2.2 Crevice Corrosion
 Crevice corrosion occurs at shielded areas that contain small
volume of aqueous solution.
 Crevice can be a hole, a space between the surface and a poorly
adherent coating.
 Principle :
1. Liquid entry but stagnant
2. Corrosion rate of crevice is higher than that on bulk (outside)
3. Crevice corrosion is initiated by changes in local chemistry
within the crevice;
i. Depletion of oxygen in the crevice
ii. Depletion of inhibitor in the crevice
 Oxygen concentration can develop when there is a difference in
oxygen concentration on a moist surface of a metal that can be
oxidized.
 Example :
1. a drop of water/ moisture on the surface
2. the oxygen concentration are lesser on the surface
3. the surface that low in oxygen concentration are cathodic
4. the surface that has higher oxygen concentration are anodic
5. because there is anodic and cathodic, the surface below the
water drop are corroded (anodic)
6. the water drop act as electrolyte
 Usually occurs at a bad gasket pipe flange, under bolt head and
connections that soaked in liquid.

5.2.3 Intergranular Corrosion
 Is a localised attack along the grain boundaries, or immediately
adjacent to grain boundaries, while the bulk of the grains remain
largely unaffected.
 It is occur when different potential between atoms at the grain-
boundaries and create the boundaries of anode and cathode.
 It is usually starts from the surface and accelerates internally
causing by bad internal structure.
5.2.4Stress Corrosion Cracking (SCC)
 It is refers to cracking caused by the combined effects of tensile
stress and specific corrosion environment acting on the metal.
 Usually occurs in alloys not in pure metals and in certain
environment, examples : copper cracked in ammonia or
aluminium alloy cracked in chloride solubility.
 The stress in the materials must has its compressive component
and the presence of both stress and corrosion environment which
causing the cracks to form and spread.
 The stress corrosion cracking usually occurs between crystals.

5.3 Corrosion Control
 Cathodic protection is the protection of a metal by connecting it to
a sacrificial anode or by impressing a direct current voltage to
make it a cathode.
 Anodic protection is the protection of a metal which forms a
passive film by the application of an externally impressed anodic
current.
 Example (steel hulls of ships adjacent to the bronze propellers) :
i. steel is an anode and bronze is a cathode and both are in
sea-water which act as electrolyte
ii. the steel (hulls) will be corroded because of its anodic, so a
more anodic material than steel and bronze is used as
corrosion sacrificial which it is zinc
iii. zinc blocks are fitted to hulls so that the electrochemical
corrosion process will occur only to the zinc
iv. the zinc blocks must be replace time to time because its
worn out of corrosion as shown below
5.4 Material Selection
 When selecting materials for engineering design, use materials
that are corrosion resistant for a particular environment and
corrosion handbook or materials data should be consulted to make
sure the proper material is used.
 Also, the material positions in electrochemical series need to be
notified.

 There are few combination between metal and good corroded
environment and economical are shown below :
i. stainless steel – nitrite acid
ii. nickel and alloy nickel – caustic
iii. monel – hydrofluoric acid
iv. hastelloi (chlorimet) – hot hydrochloric acid
v. plumbum – liquidify sulphuric acid
vi. aluminium – unpolluted atmosphere exposion
vii. tin – distillation water
viii. titanium – hot oxidation liquid
ix. tantalum – definite resistant
x. steel – sulphuric acid
5.5 Coating
 Plastic and oil are non metal material use mainly for coatings.
 Metallic coatings which differ from the metal to be protected are
applied as thin coatings to separate the corrosive environment
from the metal. Metal coatings are sometimes applied so that they
can serve as sacrificial anodes which can corrode instead of the
underlying metal.
 Metallic coatings :
1. Noble coating
o it is a coating where higher potential electrode compared
to the base metal will be protected
o base metal coating such as cuprum, nickel and chromium
as the coating and entering the holes in material
o it cannot protect the base metal if there is holes in the
coating
o it is because the base metal will become anode

2. Sacrificial coating
o the base metal protected by sacrifice it and the coated acts
as anode
o organic and inorganic coatings
o the organic and inorganic material are used to protect the
surface from contacting with oxygen or giving the basic
protection by coated with stable material which cannot be
penetrated by humidity/ moisture
o organic coating such as paint, tar, oil and varnish
o inorganic coating is enamel, plastic. Plastic is the main
inorganic materials used as coating by hot dipping and
spraying of corrosion resistant material
5.6 Design
 Designing rules :
1. considering corrosion penetration with the need of
mechanical strength when determining the thickness of a
metal used. It is important for piping and tank with liquid
contents
2. welding is better than riveting for contena to reduce crevice
corrosion.
3. use one type of material only for the whole structure to
prevent galvanic corrosion.
4. avoid extra stress and stress concentration in corroded
environment to prevent from crack-stress corrosion. Sharp
edges of component need to be avoided because it can caused
the stress
5. designing simple attachable system or changeable component
if predicted it is easier to break or fail in the service

5.7 Painting
 Paint the surface of metal to avoid corroded material from
contacting the surface.
 Paint may be applied by brushing, spraying and dipping.
 It may be dried naturally or by stoving.
5.8 Electroplate Metal
 Electroplating is the process of using electrical current to reduce
cations of a desired material from a solution and coat a conductive
object with a thin layer of the material such as a metal using
electrolysis.
 Electroplating and metal finishing processes include copper
plating, nickel plating, zinc plating, silver plating, tin plating, brass
plating, cadmium and chrome finishes.
 Metals plated include brass, copper, bronze, chrome, nickel, and
black nickel, silver and gold.
 The process :
i. the metal/ components to be plated are immersed in a
solution called electrolyte
ii. electrolyte allows the passage of an electric current
iii. the parts that require coating, are then placed in the solution
and given a negative charge/ terminal (as cathode)
iv. anodes are connected to the positive terminal
v. upon the passage of an electric current metal ions are
transferred from the electrolyte onto the surface of the
cathode
 Electroplating allows for increased corrosion resistance, scratch
resistance, decorative finishes and high temperature protection.
 Examples : tin plating and tin alloys for food container and food
contact applications.

5.9 Oxide Layers
 Oxide layers such as zinc oxide and aluminium.
 It is higher in density and therefore preventing the oxygen and
water from corrode the metal.
 The oxide layers also used as electroplating for metal products.
 Example : zinc oxide layers for steel roofs manufacturing.
5.10 Alloys
 A metal alloy is a combination of two or more metals or a metal
and a nonmetal.
 Alloys are made to improved corrosion resistance.
 Steels usually alloyed with chromium and manganese to gain
stainless steel.
5.11 Non-Ferrous Metal
 Metals and alloys are commonly divided into these classes :
1. ferrous metals : that contain a large percentage of iron
2. non-ferrous metals : that does not contain iron or only a
relatively small amount of iron
3. a metal alloy : is a combination of two or more metals
or a metal and a nonmetal
 Common non-ferrous metals used in engineering are :
a) Aluminium h) Chromium
b) Silver (Argentum) i) Gold (Aurum)
c) Copper (Cuprum) j) Molybdenum
d) Plumbum/ Lead k) Magnesium
e) Tin (Stanum) l) Cobalt
f) Nickel m) Manganese
g) Zinc

 Main properties of non-ferrous metals :
1. low strenght
2. good thermal and electric conductivity
3. free from magnetic field
4. high corrosion resistance
5. easier in manufacturing

5.11.1 Types of Non-Ferrous Metals, Physical Properties, Mechanic Properties and
the Applications
Types Desription
1. Aluminium, Al Applications:
i. wrapper
ii. light inversion
iii. decorative product
iv. coating for corrosion resistance
Characteristics:
i. tensile strength 100 N/mm2
ii. compressive strength 100 N/mm2
iii. hardness 40 HB
iv. ductility 30% elongation
v. melting temperature 660o C
vi. density 2.7 g/cm3
vii. high corrosion resistance in water and atmosphere due to the
formation of a very thin passive film of aluminium oxide on
aluminium surface
viii. good in thermal and electrical conductivity
ix. good thermal and light inverter
Physical Properties:
i. light weight
ii. widely used in casting component
iii. easier formation of oxide causing high in cost for aluminium
production from its ore (bauxite) by using electronic method
because reduction agent method are not practical
iv. aluminium oxide has its benefit as corrosion protector because
its blocking the oxygen from contacting to the metal and
avoiding the corrosion from occurred
v. aluminium oxide are hard and wear resistant in properties
vi. good electric conductor
Mechanical Properties:
i. good machinability, formability, workability and castability
ii. can be rolled to any desired thickness, stamped, drawn,
hammered, forged and extruded to almost any shape and size
Types of Aluminium Alloy:
1. Aluminium-Magnesium alloy (Al-Mg)
a. 0.14% Cuprum
b. 0.5% Silicon
c. 0.7% Ferrum
d. 0.5% Chromium
e. 5.0% Magnesium
 strength : 3x than pure aluminium
 hardness : 80 HB
 good corrosion resistance
 applications : hulls (badan kapal) and connected using rivet or
TIG weld, automotive gas or oil channel

2. Aluminium-Manganese alloy (Al-Mn)
 containing : 1.5% manganese
- to increase the tensile strength 200 N/mm2
 good corrosion resistance, formability and weldability
 applications : house roof, types of container, bus and lorry
bodies, cooking utensils, oil tank and pipe
3. Duralumin
 containing : 4% cuprum (copper)
 a strong alloy with tensile strength for 400 N/mm2 after heat
treatment
 applications : for manufacturing of aircraft body, wire, rivet,
metal plate and moulding boxes
4. Aluminium - Silicon alloy (Al-Si)
 containing : 10% - 13% silicon
 tensile strength : 230 N/mm2
 high corrosion resistance against salt water and atmosphere
 applications : in casting process for ship block engine and car
engine, gear box, shaft and crank box
5. Aluminium - Cuprum alloy (aluminium casting)
 containing : 1.5% - 4.0% cuprum (copper)
 after heat treatment gaining the tensile strength upto 650
N/mm2
 applications : high speed engine block for cars and aircraft
6. Aluminium – Zinc alloy (Al–Zn)
 containing : zinc, magnesium, cuprum, small amount of
manganese and chromium
 high in tensile strength, good corrosion resistance and can be
heat treated
 applications : widely used for aircraft parts structure where
higher strength are needed
7. Aluminium + 0.1% Cuprum + 0.7% Ferrum + 0.1% Manganese
 for electric conductor and equipment which does not apply
force
 applications : construction decorative equipment, metal boxes,
bottle caps, cooking utensils
8. Aluminium + 0.1% Cuprum + (1.7-7.5)% Magnesium + Ferrum
+ Manganese
 applications : ship structure, cars, rivet, bar and fences
9. Heat-treatable forged aluminium
 applications : for machine manufacturing, houses and aircraft
frame structure
 used for components that can withstands stress/ force but
lighter such as mould equipment for casting, gear box, aircraft
structure, cylinder head, piston and for the usage of good
corrosion resistance

2. Copper/Cuprum,
Cu
Applications: cables, television and radio equipment, switch, water
carrying pipes, soldering material, cooking pot, ship bodies
Main Properties:
ii. compressive strength 300 N/mm2
iii. hardness 80 HB (casting type)
90 HB (cold work)
66 HB (cold work and annealing)
iv. ductility upon elongation 25% (casting type)
55% (annealed)
3% (cold work)
v. melting temperature 1083 oC
vi. density 8.9 g/cm3
vii. resistance over atmosphere and water corrosion
viii. good electric conductor
i. good electrical conductor – used as conductors in pure state
ii. the tensile strength for pure copper about 300Nmm-2 and when
alloyed, increased upto 460 Nmm-2
iii. excellent heat transfer
Types of Copper Alloys:
1. Bronzes
 is an alloy of copper containing elements other than zinc but
cuprum are the main material
 properties :
1. higher strength
2. better corrosion resistance
3. antifriction or bearing properties
4. malleable
5. ductile
6. excellent electrical conductor
7. excellent alloying characteristics
8. non-magnetic
9. machinable
3. Brasses Properties:
i. higher strength
ii. good thermal and electrical conductivity
iii. good atmospheric corrosion resistance
iv. high machinability
v. ductility
vi. hardness
vii. wear resistance
viii. recyclability
Types of Brasses:
1. Brass with 63/37 (basic brass)
 suitable for casting process and hot-worked
 it is brittle after cold-worked but can be formed by casting,
forging, hot rolling and extrusion process

2. Brass with 70/30 (cartridge brass)
 ductile and can be drawn upto 70% of elongation
 the tensile strength : 600 N/mm2 (hard)
320 N/mm2 (after cold-worked)
 hardness : 60 HB (annealed)
130 HB (in drawing process)
 applications : wire, pipe and rod
 widely used in drawing operations to produce cartridge cases
3. Brass with 60/40 (muntz metal)
 suitable for hot-works such as hot-stamping and hot forging
 tensile strength : 450 N/mm2 with low ductility and hard to
machined
 1% tin added to gain corrosion resistance
4. Zinc Applications: coating material for steel to prevent corrosion such as for
iron chains, house roof, kitchen utensils, water tanks, car batteries,
tooth patch material and basic material for paint
Main Properties:
ii. hardness 80 HB (zinc alloy)
iii. melting temperature 420C
iv. density 7.1 g/cm3
i. basic usage of zinc is for steel coating to prevent corrosion
ii. example : galvanic electroplate such as steel coated with zinc
for bolt, screw, fences, pipe, tank
iii. pure zinc has the crystallization temperature in room
temperature, so it can annealed itself and cannot be worked
(hardened) in room temperature
iv. zinc less pure graded will shows an increasement in hardness
and strength in usage
v. applications : as coated for iron and steel (galvanized iron),
printer blocks, tube, roof plates
i. brittle in normal temperature and can be forge at the
temperature 100°C - 150ºC
ii. at 200°C, it become more brittle and can be form in powder
iii. corrosion resistance
5. Lead
Plumbum, Pb
Applications: water pipe, cable coating, coating for chemical container,
weights and counter-balances, shielded against x-ray and radiation-
rays in nuclear plant and as alloy in tin as solder metal
Main Properties:
ii. hardness 4 - 8 HB
iii. melting temperature 327C
iv. density 11 g/cm3

i. a heavy metal
ii. high in density
iii. low melting point
iv. good resistance to corrosion
v. soft
vi. malleable
vii. possesses low strength
viii. good lubricating properties
ix. high absorbing power for radiations, such as x-rays
x. good heat and electric conductor
6. Bearing Material Mechanical properties :
i. high compressive strength so it does not squeeze out under
heavy loads
ii. high hardness and wear resistance to provide a longer life
iii. good thermal conductivity to prevent the bearing metal from
becoming overheated
iv. resistance to corrosion
v. able to retain oil
vi. antifriction quality
Types of Bearing Materials :
1. White metal alloy
 divided into the tin-base and the lead-base alloys
2. Phosphor bronzes
 used for heavy loads at low speeds
3. Poly-tetra-fluoro-ethane (P.T.F.E) or Teflon
 it is a non-metallic material and it is a thermoplastic
material
 used under light loads and at low speeds

Metal Properties Applications
Aluminium  Lightest of the commonly used
 High electrical and thermal
conductivity
 Soft, ductile and low tensile
strength
 The base of many engineering alloys
 Lightweight electrical conductors
Copper  Soft, ductile and low tensile
strength
 Much easier to joint by
soldering and brazing
 Corrosion resistant
 The base of brass and bronze alloys
 It is used extensively for electrical conductors and
heat exchangers such as motor car radiators
Lead  Soft, ductile and very low
tensile strength
 High corrosion resistance
 Electric cable sheaths
 The base of „solder‟ alloys
 The grids for „accumulator‟ plates
 Lining chemical plant
 Added to other metals to make them „free-cutting‟
Silver  Soft, ductile and very low
tensile strength
 Highest electrical conductivity
of any metal
 Widely used in electrical and electronic engineering
for switch and relay contacts
Tin  Resists corrosion  Coats sheet mild steel to give „tin plate‟
 Used in soft solders
 One of the bases of „white metal‟ bearings
 An alloying element in bronzes
Zinc  Soft, ductile and low tensile
strength
 Corrosion resistance
 Used extensively to coat sheet steel to give
„galvanized iron‟
 The base of die-casting alloys
 An alloying element in brass
Chromium  Resists corrosion
 Raises strength but lowers
ductility of steels
 Improves heat-treatment
properties
 Used as an alloying element in high-strength and
corrosion resistant steels
 Used for electroplating
Cobalt  Improves wear-resistance and
„hot hardness‟ of high-speed
steels
 Used as an alloying element in „super‟ high-speed
steels and in permanent-magnet alloys
Manganese  High affinity for oxygen and
sulphur
 Soft and ductile
 Used to de-oxidize steels and to offset the ill-effects
of the impurity sulphur
 Larger amounts improve wear resistance
Molybdenum  A heavy, heat-resistant metal
that alloys readily with other
metals
 Used as an alloying elements in high-strength nickel-
chrome steels to improve mechanical and heat-
treatment properties
 It reduces mass effect and temper-brittleness
Nickel  A strong, tough, corrosion
resistant metal widely used as
an alloying element
 Used as an alloying element to improve the strength
and mechanical properties of steel
 Tends to unstabilize the carbon during heat
treatment, and chromium has to be added to
counteract this effect in medium and high-carbon
steels
 Used for electroplating

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