MSE 258:Physical Metallurgy of Non-Ferrous Metals

Dr. Emmanuel Kwesi Arthur

Department of Materials Engineering,

Kwame Nkrumah University of Science and Technology, Kumasi

2019

Lecture Nine

Magnesium and Magnesium Alloy

First produced in 1808. Is the lightest engineering metal available, with good vibration damping characteristics.

Not sufficiently strong in pure form but alloyed to increase strength.

Magnesium is an alloying element in various nonferrous metals. Used to strengthen material due to its strong form.

Used with Aluminium to make lightweight alloys.

Magnesium comes from sea water through electrolysis or by thermal reduction.

Magnesium

Burns easily when being machined

Magnesium is flammable, but this is only a problem when it is in the form of powder or very thin sheet.

Magnesium and magnesium alloys

Pure Mg

Tm – 649 °C

Density – 1.740 g/cm3 (lightest among the engineering materials)

Mg-alloys

- Mg – Mn (up to 2.5 %)

- Mg – Al – Zn (up to 10 % Al, 5 % Zn)Heat treatment of Mg-alloys

Similar to Al-alloys

Quenching + age hardening

4

Magnesium and its alloys

• Disadvantages

• Difficulty in melting process due to high reactivity

• Low elastic modulus• Limited cold workability and

toughness (hcp structure)• Limited creep resistance at elevated

temperatures (Tm = 650°C)• High degree of shrinkage on

solidification (high thermal expansion)• High chemical reactivity (free 3s2

valence electron structure)• In some applications limited corrosion

resistance (electrode potential v = -2.31 V)

Magnesium side panels

Handy cam & mobile

phone bodies

Mg alloys Application

Mg alloys for automotive

Magnesium Wheel

Magnesium - aluminum phase diagram

Wrought magnesium alloys are based on alloys of magnesium (Mg) with 3 - 8% aluminum (Al), some with additions of zinc, manganese or copper.

Cast magnesium alloys are based on alloys of magnesium (Mg) with 2 -9% aluminum (Al), some with additions of zirconium, manganese or copper.

Designation of various Mg alloys The classification system of the American

Society for Testing Materials (ASTM) is the most widely used.

In this system, the first two letters indicate the principal alloying elements

The letter corresponding to the element present in the greatest quantity is used first; if they are equal, they are listed alphabetically.

The letters are followed by numbers that list the amount of the principal alloying elements in weight % rounded to the nearest whole number; thus AZ91 means the alloy 90% Mg, 9% Al and 1% Zn;

A = aluminum, C = copper, E = rare earths, K = zirconium, L = lithium, M = manganese, S = silicon, Z = zinc.

Cast Magnesium Alloys and their applicable temperatures

Mg-alloys

deformable (ex MgMn2)

cast alloys (ex designation MCMgAl8 / material No. MC21110)

Deformable Mg-alloys

Mg cast alloys (EN173)

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DesignationA

%Applications

MgMn2

MgAl8Zn

• 145

310 215

15

6

Corrosion resistant, weldable cold formable; conteiners, car , aircraft and machine manufacturing

MCMgAl8Zn1

MCMgAl6

MCMgAl4Si

240 90

190-250 120-150

200-250 120-150

8

4-14

3-12

Good castability. Dynamically loadable. Car and aircraft manufacturing.

Designation