Mg alloys

Question 1

Where is Mg in nature?

Answer 1

Mg is found in sea water,in minerals and rocks.
Through dehydratation of water is found MgCl^2 then Mg is extract by electrolytic cells.

Question 2

Extraction of Mg

Answer 2

• Preparation of MgCl^2 by dehydratation
• Extraction of Mg in electrolytic cells

Question 3

Mg features

Answer 3

• Atomic diameter of Mg allows many solid solutions, but commercially are developed only few simple alloy
• Mg alloys has poor formability and ducility at room temp, it significantly increases at temp above 250°C.

Question 4

Magnesium pros in casting

Answer 4

• Low melting temp.
• High fluidity
• low specific heat that means fast cooling
• Low density

Question 5

Plastic forming in Mg

Answer 5

Suitable only in the range of 300-500 °C cold forming, extrusion is not possible.

Question 6

Mg-Al alloy

Answer 6

• Segregation induces the formation of non eq constituents
• Solution annealing and aging are feasible but the response generally makes it not convenient

Question 7

Zr in Mg alloy

Answer 7

• Zr also allows to remove hydrogen
• To achive high strength is used Zr with Zn RE Th Ag Y
• Zr is incompatible with Al
• Mg and Zr cn react on cooliong

Question 8

Wrought Mg alloy

Answer 8

• Thermo-mechanical treatments induced by plastic deformation improve all properties
• Anisotropy in tension vs compression behaviour.

Question 9

Reason for anisotropy

Answer 9

• Stress strain anisotropy in a wrought Mg alloy is favored by the orientation of the basal planes of the cells that is preferentially oriented to the load direction

Question 10

Thermal treatment of Mg alloys

Answer 10

• Mg-Al alloys solution annealing and agin do very low effect
• Possible benefits come from solution annealing plus removing eutectic segregation
• in Zr alloy the strengthening effect of aging is much higher

Question 11

Corrosion behaviour

Answer 11

• The surface oxide is unstable under 10.5 on ph scale
• An exception is HF wich generates a passivating film
• Mg is the worst corrosion resistant metal
• It get better resitance with a oxide layer of Mg(OH)^2
• Strong electro-chemical effect produced by impurities; they behave like cathodes. For high quality casting scraps are not directly remelted

Question 12

Mg casting practise
(issues of Mg in casting)

Answer 12

• The protection of molten Mg from oxigen is fondamental
• Above 850°C spontaneusly combustion develop
• The layer of oxide on layer doesen’t protect the underlying metal
• Shielding gas to protect the bath

Question 13

Mg machinig practise

Answer 13

• Caution for chip burning
• Dry machining is feasible but preferrable with a lubricant
• Mg is among the best machinable metals due to excellent surface finishing and interrupted chips.

Question 14

Application of magnesium

Answer 14

• Car
• Phones
• Light weight
• Electromagnetic radiations shielding