Light Alloys- Magnesium 1

Question 1

Mg applications in WW2

Answer 1

First airplane nearly completely designed with Mg. World’s largest bomber contained 19,000lbs of Mg

Question 2

Mg applications in peace time

Answer 2

Transportation, aircraft/aerospace, 3C product, military, healthcare

Question 3

Crystal structure of Mg

Answer 3

hcp

Question 4

Advantages of Mg

Answer 4

Lowest density of all construction metals at 1.74g/cm3 so light construction parts possible. High specific strength. Excellent castability. Good machinability. Improved corrosion resistance with high-purity alloys. High damping properties. Good weldability under inert gases. Integrated recycling possible

Question 5

Disadvantages of Mg

Answer 5

Cold working and extrusion abilities very poor due to hcp structure. Low corrosion resistance. Easily flammable with oxygen around melting points. Shrinkage about 4% when solidifying and 5% during cooling. Low toughness and strength

Question 6

Calcination

Answer 6

Cheapest. Heat MgCO3 to produce MgO and mix with petroleum coke and heat to separate O from Mg. Bad for environment

Question 7

Pidgeon process

Answer 7

Thermal reduction method. Powdered ferrosilicon and MgO heated under vacuum at 1200°C giving Mg vapour which is then condensed

Question 8

Dow process

Answer 8

Dolomite CaMg(CO3)2 and seawater and treated with HCl to give MgCl2 and put in electrolytic cell to give Mg metal at cathode

Question 9

How many independent slip systems need to be active at the same time for plastic deformation?

Answer 9

5

Question 10

How does CRSS compare for twins and slip in Mg?

Answer 10

Basal slip lowest. Then {10-12} twin. Then prismatic slip. The pyramidal slip. Then {10-13} twin. Then {10-11} twin highest. All decrease as T increases

Question 11

When is Mg mostly used for engineering applications?

Answer 11

When it is alloyed with other elements. Even though 99.8% purity readily available