MAGNESIUM AND ITS ALLOYS

MOIZ ULLAH BAIG (MM-036)

SAAD ARIF (MM-026)

HARIS IQBAL KHAN (MM-020)

OMAR SIDDIQI (MM-004)

DISCOVERY

• In 1755

• By Joseph Black

• At Edinburgh, England

• Name derived from Greek word ‘Magnesia’

• About 2.4% of the Earth’s crust contains Magnesium making it the 6th

most abundant element.

ATOMIC STRUCTURE

Atomic Number: 12

Atomic Mass: 24

Group: Alkaline Earth Metal

Configuration: 1s2, 2s2, 2p6,

3s2

PROPERTIES

• Color: Silvery white metal

• Phase: Solid

• Crystalline Structure: Hexagonal

• Melting Point: 651 °C

• Boiling point: 1100°C

• Specific Gravity: 1.74 gm/cm3

• Burns in air with a bright white light.

APPLICATIONS• Aircraft and missile industries

• Photo-engraving

• Deoxidizer and desulfurizer in the

manufacture of nickel and copper alloys

• Magnesium anodes provide effective

corrosion protection

• Automotive wheels, housings, transmission

cases

• Bicycles and other sporting goods

equipment

• Laptops, televisions, cell phones

MAGNESIUM ALLOYS

• Metal for the 21st century.

• Alloying is used to improve the formability of magnesium

• Most versatile material choices amongst the structural

materials.

• High strength-to-weight ratio.

ALLOY DESIGNATION

• The letters stand for the two major alloying elements,

- first letter is the highest amount.

- second letter is the second highest amount.

• The numbers stand for the amount of the two major alloying

elements,

- first number following the letters stands for the

wt.% of the first letter element.

- second number stands for the wt.% of the second

letter element.

Alloying Element Effects of Addition

Aluminum (Al) Increases hardness, strength, and castability while only increasing density minimally.

Calcium (Ca) Improves thermal and mechanical properties as well as assists in grain refinement and

creep resistance. Also, it reduces surface tension.

Cerium (Ce) Improves corrosion resistance. Also, it increases plastic deformation capability, magnesium

elongation, and work hardening rates. But it reduces yield strength.

Copper (Cu) Assists in increasing both room and high temperature strength.

Manganese (Mn) Increases saltwater corrosion resistance within some aluminum containing alloys.

Nickel (Ni) Increases both yield and ultimate strength at room temperature. Negatively

impacts ductility and corrosion resistance.

Strontium (Sr) Used in conjunction with other elements to enhance creep performance.

Tin (Sn) When used with aluminum it improves ductility and reduces tendency to crack during

processing.

Yttrium (Y) Enhances high temperature strength and creep performance when combined with other

rare earth metals.

Zinc (Zn) Increases the alloys fluidity in casting.

When added to magnesium alloys with nickel and iron impurities, it can improve corrosion

resistance.

EFFECTS OF ALLOYING ELEMENTS

MAGNESIUM-ALUMINUM BINARY ALLOY SYSTEM

• Increases hardness

• Improves strength

• Slightly increases density

MAGNESIUM-ALUMINUM BINARY PHASE DIAGRAM

Liquid

Fcc-Al Mg-Hcp 0.31

0.120.84

1 0.8 0.6 0.4 0.2 0 300

400

500

600

700

800

900

1000

𝛾 = Al 12 Mg 17

+𝛾 Mg-Hcp Fcc-Al + Al 140 Mg 89

723 K 732 K 705 K

Mole fraction (Al)

683 K

𝛾

SCHEMATIC VIEW OF EUTECTIC MICROSTRUCTURE OF MG-AL

ALLOY• Primary α-Mg

Pure Mg Dendrites

• Intermetallic phase

β-phase i.e.

Mg17Al12

MAGNESIUM-ALUMINUM GRAIN SIZES

(a) Mg-1%Al (b) Mg-5%Al (c) Mg-6%Al (d) Mg-9%Al

Grain sizes of binary Mg-Al Alloys

HV: 15kv 20.5µ

m HV: 15kv 20.5µ

m HV: 15kv 20.5µ

m HV: 15kv 20.5µ

m

• Reduces grain size and improves ultimate tensile and yield strength

EFFECT OF STRONTIUM ADDITION

• Distributed along the grain boundaries

• Lamellar structure formed

• Better creep resistance can be obtained

SEM photos of the as-cast alloys. (a) AJC411and

(b) AJC511

(a) AJC411 (b) AJC511

MAGNESIUM-ZINC BINARY ALLOY SYSTEM

• Have a strong age hardening response.

• Heat-treatable high strength can be potentially developed.

MAGNESIUM-ZINC BINARY PHASE DIAGRAM

MAGNESIUM ZINC GRAIN SIZES

Grain sizes of binary Mg-Zn alloys, (a) 0.2 at.%, (b) 0.7

at.%

(a) (b)

• Reduces with increase in concentration of Zinc

(Zn)

EFFECT OF ZIRCONIA ADDITION ON GRAIN SIZE

• Enhances the homogeneity by making the grains round

• Reducing the amount of eutectic at the grain boundaries

• Contribute positively to the strength of the alloy

CORROSION RESISTANCE

• Depends upon,

1) The alloying element

2) The amount present

3) Humidity

4) Indoor or outdoor exposure.

• The effect of heat treatment on the corrosion resistance of magnesium

alloys in salt solution.

FORGING OF ALLOYS

• Magnesium alloys are best known for their low

density, which results in forgings with very low weight.

• The problem in magnesium forging is cracking which

results from coarse grain sizes.

• This can be overcome by additional extrusion process

to give sufficient grain size for forging. High-value automotive wheels

are among the most

recognizable applications for

forged magnesium alloys.

JOINING OF MAGNESIUM ALLOYS

• Shielded-metal arc welding

• Gas welding

• Electric resistance seam and spot welding

• Riveting

• Bolting

• Adhesive bonding

ADVANTAGES AND DISADVANTAGES OF MAGNESIUM ALLOYS FOR ENGINEERING

DESIGN

Advantages:

• Good machinability.

• Good creep resistance to 120 C.

• High thermal conductivity.

• Easily gas-shield arc-welded.

Disadvantages:

• High tendency to galvanic corrosion when contact with dissimilar metals or

electrolyte.

• Difficult to deform by cold working.

• High cost.

REFERENCES:

• Introduction to Physical Metallurgy 2nd Edition – Sidney H Avner

• Materials and Processes in Manufacturing 10th Edition – Paul DeGarmo

• http://www.mdpi.com/journal/metals/special_issues/magnesium_technology

• http://www.rsc.org/periodic-table/element/12/magnesium

• http://www.elementalmatter.info/magnesium-properties.htm

• http://www.intlmag.org/magnesiumapps/overview.cfm

• http://www.totalmateria.com/Article78.htm

• https://www.forging.org/design/47-magnesium-alloys

• http://forgingmagazine.com/expert-advice/forging-magnesium-alloys