Electrical conductivity and mechanical properties oi magnesium

1. Electrical Conductivity and
Mechanical Properties of Magnesium

2. Introduction and Facts
 It has one of the lightest structure of all non-ferrous metal and its one of the most important
properties is its strength-to-weight ratio.
 It lavishly available on the earth’s crust, comprising 2.7%.
 In nature it doesn’t occur in metallic form, it is mostly found in the form of magnesium
compounds.
 Its atomic structure consists of 12 protons, 12 neutrons and 12 electrons and has closed
packed hexagonal crystal structure. Due to which its deformation takes place along the basal
place at room temperature and at high temperature (above 204℃) deformation takes place
along the prismatic planes. [1]
 Major source of magnesium is ocean water as it consists of 0.13% of world’s oceans.

3. Production Process
 In manufacturing industry, currently there are following two basic processes which are in
practice to produce magnesium and recently third method is developed:-
Electrolysis Process – In this process dry magnesium chloride is separated from chloride with the help of
electrolysis process to collect magnesium and form ingots. Magnesium chloride comes from sea water
and its accounts of 80% of total production worldwide. It is similar to aluminium electrolysis process
and in the end magnesium chloride or oxide is reduced to chloride gas and magnesium ingots. [2]
Thermic Reaction - In this process dolomite, which consists of calcium magnesium carbonates is
calcined to magnesium oxide and lime with the help of silicon. Resulting in yielding of magnesium gas
and slag of dicalcium silicate. Magnesium gas forms in to crystals in condenser under reduced pressure
is melted and formed into ingots for further usage. [2]

4. Mechanical
Properties of
Magnesium and
it’s Alloys
 This section of PPT contains information about how certain
mechanical properties can be achieved by add certain
amount of another material (alloy) into the magnesium.
Some of the properties discussed are as following:-
Tensile Strength
Elastic Moduli
Compressive Strength
Damping Capacity
Section also includes list of general common alloys and
there specific property according to its application. Some of
the common mixtures are:-
Magnesium-Aluminium
Magnesium-Calcium
Magnesium-Lithium
Magnesium-Zinc

5. Tensile Properties
Some of the properties such as ultimate tensile strength, breaking stress, maximum elongation
and reduction of area can be measured via tensile test. Specimen of magnesium is designed
specially according to the purpose of test and testing method. Following Fig 1 shows values at
room-temperature. [3]
To increase tensile properties of magnesium one of the common material used is aluminum. It is
preferred to sand casting process manufacture parts from magnesium - aluminum alloy. It
provides good combination of tensile strength, elongation and yield strength. [3]
FIG 1

6. Compressive Strength
It is property of the material to sustain pressure and maintain its molecular structure when
load is applied. It is measured on universal testing machine. Atoms in solids tends to create
equilibrium position by repositing atoms as they are forced together when compression load is
applied. [4]
Compressive strength of material corresponds to the stress-strain curve defined by following
equations:-
FIG 2

7. Elastic Moduli
It is a quantity which measures material’s resistance to deform elastically when stress is
applied. There different types of elastic moduli, specifying how and when stress and strain is to
be measured [5]:-
Young’s Modulus
Shear Modulus
Bulk or Volumetric Modulus.
Elastic Moduli is related to ductility of the material and it can be achieved highest by creating alloy of
magnesium and zinc. Such as Magnesium-Zinc-Zirconium and Magnesium-Zinc-Thorium. Alloys of this
kind eliminates columnar cast structure and course grains resulting in good combination of tensile
strength and ductility. [6]
Fig 3

8. Surface Tension
Surface tension is an important property for magnesium alloys to
prevent corrosion, as often various types of surface coating is done
when exposed outdoor. [7]
Surface Tension is the tendency of material (when it is in liquid state) to
resist external load or force due to its molecular its force of attraction. In
the case of magnesium coating properties of surface tension dictates
whether spray will spread or retract on solid surface, it will be dry or
wet. It depends on cohesive and adhesive forces between molecules of
parent metal and magnesium. [7]
The contact angle between the solid surface and liquid is measured in
degree of wetting. Larger the contact angle and larger surface tension
will result in smaller degree of wetting. Wetting (Θ < 90 degrees) occurs
when cohesive forces are less then adhesive forces. Vice versa de-wetting
occurs when Θ is greater then 90 degrees. [7]
FIG 4

9. Poisson's Ratio
It is ratio between lateral strain to longitudinal strain which measures deformation (contraction
or expansion). It is an important mechanical properties of magnesium alloys, as it has significant
effect on amount of work required to manufacture large pieces. [8]
Poisson’s ratio of magnesium is 0.28 and for magnesium alloys it ranges between 0.280-0.350.
When cold or hot working is done on any solid, Poisson's ratio is a key aspect as it helps to
determine dimensional difference between actual and processed value.

10. Hardness and Wear Resistance
Almost all the magnesium alloys have sufficient hardness for different kind of structures. Varies
kind of magnesium alloys with wide range of hardness value can be manufactured but resistance
to abrasion varies between 15% to 20% only. [9]
Magnesium can be protected from heavy bearing load, frequent removal of material by adding
inserts of non metals, steel or bronze between two moving parts. Inserts can be added by
pressing, riveting, bolting etc. [9]
Magnesium alloys can provide satisfactory results for following conditions:-
Sufficient lubrication between moving parts.
Applied load should not exceed 14MPa.
Operational temperature should not exceed 105℃. [9]

11. Damping Capacity
 It is ability of a material to absorb and convert mechanical
energy into heat energy. All the magnesium alloys has good
damping capacity compare to other metals. Alloy or material
with high damping capacity absorbs vibration which cause
unwanted stress and strain in parts. [10]
Low density of magnesium makes it possible to
manufacture thicker and big parts which can operate quietly
and generates less vibration. [10]
Wrought alloys of magnesium have very high damping
capacity. Due to which it has become important material for
manufacturing engines, as it reduces vibrations effectively, it
is corrosion resistant, and reduces weight of engine
significantly. [10]
Fig 5

12.  Fig 12 represents
nominal composition
and mechanical
properties of
Magnesium Alloys at
room temperature.
CHART - A
Fig 6

13. Electrical
Conductivity
Properties of
Magnesium
Alloys
This section of PPT contains information about electrical
properties of magnesium, which includes:-
Electrical Conductivity
Electrical Resistivity
Electrochemical Equivalent

14. Electrical Conductivity and Resistivity
It is a property of a material to conduct electric current. Whereas, electric resistivity is
reciprocal of electrical conductivity. It represents ability of material to resist electric current. [11]
Electrical resistivity of magnesium is 43.9 nΩ·m (at 20 °C).
Magnesium has galvanising corrosion effect on electric contact. Due to which insulation is
required.
Copper rich Cu-Mg alloys are used to manufacture automotive switches, relays, wire harness,
telecommunication cables, conductor wires etc. Magnesium maintains electrical conductivity
and adds tensile strength to the alloy, which is necessary for outdoor applications. [12]

15. CHART - B
Fig represents change in
electrical resistivity of magnesium
alloys according to alloys weight
percentage in mixture.
Fig 7

16. Electrochemical Equivalent
Electrochemical equivalent of any material can be defined as the mass of the material
accumulated to one of the electrodes when 1 Amp of electric current is applied for 1 second.
[13]
Electrochemical equivalent of unalloyed magnesium is 126 mg/Coulomb. It is an important
property of magnesium as one of the method used to manufacture magnesium and magnesium
alloys ingots is by electrolysis process; as mentioned in earlier slide. [14]
It is important to know about electrochemical equivalent property of magnesium and
magnesium alloys because electrolysis process is also used for surface coating to increase
corrosion resistivity of the alloy.

17. Following table
shows
electrochemical
equivalent of
some of the
elements
Fig 11

18. In this section of PPT, different types of magnesium alloys
are briefed.
There are four binary alloy systems, through which one can
classify magnesium alloys as following:-
Magnesium-Aluminium
Magnesium-Zinc
Magnesium-Rare Earth
Magnesium-Thorium
Apart from alloys mentioned above other alloys such as
lithium, zirconium are also briefed.
Types of
Magnesium
Alloys and
their
properties.

19. Magnesium and Aluminium Alloys
It is one of the most favourable combination to improve tensile strength, freezing range,
hardness and makes it easier for casting.
 For commercial use the wt% of aluminium hardly exceeds 10%. We can get optimum
combination of ductility and strength when aluminium content is 6%.
Examples of magnesium-aluminium based alloys:-
AZ61A has good ductility and strength, making it appropriate choice for extrusion and forging of alloy.
AZ80A alloy contains 8.5% of aluminium which is heat treatable and can be used for hot press forging
and extrusion. It provides combination of moderate elongation and strength.
With only 3% of aluminium AZ31 provides general purpose extrusion material with good formability
and strength; but it is not heat treatable.
[15]

20. Magnesium and Zinc Alloys
After aluminium, zinc is the most effective alloying
ingredient. Some of the essential alloy mixtures are
magnesium-zinc-zirconium and magnesium-zinc-thorium.
The casting alloy ZK51A and ZK61A provides best
combination of tensile strength and ductility of any
magnesium casting alloys. It is due to binary system of
magnesium and zinc results in strong age hardening effect on
microstructure of mixture.
Mixture of magnesium-zinc-thorium shows the
characteristics of lamellar form of eutectic compound along
the grain boundaries as shown in Fig 15.
[16]
Fig 7

21. Magnesium and Rare Earths Alloys
Presence of rare earth in magnesium improves its thermal
properties by obtaining precipitation at grain boundary to
minimize creep and by high recrystallization temperature.
When rare earth consists of 50% additional cerium it is
known as mischmetal and can be substituted as low-cost
commercial alloy.
This group of magnesium alloy includes following systems:-
Magnesium-Rare Earths-Zirconium
Magnesium-Rare Earths-Zinc
[17]
Fig 8

22. Magnesium and Thorium Alloys
Unlikely rare earth, thorium also elevates thermal properties of magnesium. Casting alloys can
be used between 350 to 700℃ and also provide better properties than rare earth.
These alloys have one of the best high-temperature of any wrought-magnesium alloys.
Following are the common groups of alloys used in this system:-
Magnesium-Thorium-Zirconium
Magnesium-Thorium-Zinc
[18]

23. Magnesium and Lithium Alloys
Mg-Li alloys have higher solid solubility compare to other alloys, it ranges between 5.5 wt% to
17.0 wt%. Due to its relatively low density of 0.54, it helps to lower the density of mg-Li mixture
even lower than unalloyed magnesium.
Increase in weightage of lithium in mixture will result in decrease in strength but increases
ductility. Due to which Mg-Li alloys have limited application.
Recent studies have found that Li-rich Li-Mg alloy can be used as stable anode for Lithium-
Sulfur batteries. Experiments have found that Mg helps to enable efficient surface morphology
of anode.
[19]

24. Magnesium and Zirconium Alloys
Only 0.6% of zirconium is soluble in molten magnesium. Due to low solubility Mg-Zr alloy is not
strong enough during its casting state, the addition of other material is required to achieve
desired properties and founding characteristics. This kind of alloys are majorly used in aerospace
industry.
Zirconium is added to alloys to improve two major properties:-
Tensile properties (higher ratio of yield strength to tensile strength).
Creep resistance.
Zirconium containing alloys are as following:-
Magnesium-Zinc-Zirconium
Magnesium-Rare Earth-Zirconium
[20]

25. Joining Magnesium Alloys
Magnesium and magnesium alloys can be joined by some of
the common fusion methods and fastening methods, which
includes metal arc welding, gas welding, riveting, bolting,
adhesive bonding, electric resistance seam and spot welding.
With the increase in alloy content in magnesium alloy melting
point and shrinkage decreases and solidification range
increases. Failure of welded joints usually occurs around the
heat affected zone rather than in weld itself.
Electrical properties of magnesium alloys also play vital role in
selecting type of welding process for joining.
[21]
Fig 10

26. Conclusion
 In the end, on the basis of research I would like to conclude that Magnesium and Magnesium
Alloys can be used as alternate or replacement of metals like aluminium, steel, iron etc.
according to its usage.
Its high manufacturing cost is major drawback resulting in limited applications of the alloy.
Apart from its manufacturing cost, magnesium alloys are viable and reliable source of
alternating certain metals. Also it is lavishly available on earth’s crust and sea water.
Mechanical properties of magnesium alloys can be easily achieved and modified whereas
electrical properties of magnesium alloys are limited and not up to the best.

27. Reference of Content
[1] https://www.britannica.com/science/magnesium#ref4445
[2] ASM – Speciality Handbook, Magnesium and Magnesium Alloys, P.3 1999.
[3] ASM – Speciality Handbook, Magnesium and Magnesium Alloys, P.10 1999.
[4] https://en.wikipedia.org/wiki/Compressive_strength
[5] https://en.wikipedia.org/wiki/Elastic_modulus
[6] Introduction to Physical Metallurgy, P.503 1974.
[7] http://labman.phys.utk.edu/phys221core/modules/m7/surface_tension.html
[8] https://en.wikipedia.org/wiki/Poisson%27s_ratio#
[9] ASM – Speciality Handbook, Magnesium and Magnesium Alloys, P.69 1999.

28. Reference of Content
[10] ASM – Speciality Handbook, Magnesium and Magnesium Alloys, P.170 1999.
[11] https://en.wikipedia.org/wiki/Electrical_resistance_and_conductance
[12] https://www.belmontmetals.com/magnesium-and-copper-alloys-benefits-and-applications/
[13] https://en.wikipedia.org/wiki/Electrochemical_equivalent
[14] ASM – Speciality Handbook, Magnesium and Magnesium Alloys, P.10 1999.
[15] Introduction to Physical Metallurgy, P.501 1974.
[16] Introduction to Physical Metallurgy, P.503 1974.
[17] Introduction to Physical Metallurgy, P.503-504 1974.
[18] Introduction to Physical Metallurgy, P.504-505 1974.
[19] ASM – Speciality Handbook, Magnesium and Magnesium Alloys, P.15 1999.
[20] ASM – Speciality Handbook, Magnesium and Magnesium Alloys, P.20 1999.
[21] Introduction to Physical Metallurgy, P.505-506 1974.

29. Reference of Images
Fig 1 – ASM – Speciality Handbook, Magnesium and Magnesium Alloys, P.10 (Table 12) 1999.
Fig 2 – https://en.wikipedia.org/wiki/Compressive_strength
Fig 3 – https://en.wikipedia.org/wiki/Elastic_modulus
Fig 4 – http://labman.phys.utk.edu/phys221core/modules/m7/surface_tension.html
Fig 5 – ASM – Speciality Handbook, Magnesium and Magnesium Alloys, P.11 (Fig 11) 1999.
Fig 6 – Introduction to Physical Metallurgy, P.506 (Table 12.10) 1974.
Fig 7 –ASM – Speciality Handbook, Magnesium and Magnesium Alloys, P.9 (Fig 11) 1999.
Fig 8 – Introduction to Physical Metallurgy, P.503 (Fig 12.33) 1974.
Fig 9 – Introduction to Physical Metallurgy, P.504 (Fig 12.34) 1974.
Fig 10 – ASM – Speciality Handbook, Magnesium and Magnesium Alloys, P.106 (Table 1) (Fig 11) 1999.
Fig 11 - https://en.wikipedia.org/wiki/Electrochemical_equivalent

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