Light Alloys- Magnesium 1 Flashcards
Mg applications in WW2
First airplane nearly completely designed with Mg. World’s largest bomber contained 19,000lbs of Mg
Mg applications in peace time
Transportation, aircraft/aerospace, 3C product, military, healthcare
Crystal structure of Mg
hcp
Advantages of Mg
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
Disadvantages of Mg
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
Calcination
Cheapest. Heat MgCO3 to produce MgO and mix with petroleum coke and heat to separate O from Mg. Bad for environment
Pidgeon process
Thermal reduction method. Powdered ferrosilicon and MgO heated under vacuum at 1200°C giving Mg vapour which is then condensed
Dow process
Dolomite CaMg(CO3)2 and seawater and treated with HCl to give MgCl2 and put in electrolytic cell to give Mg metal at cathode
How many independent slip systems need to be active at the same time for plastic deformation?
5
How does CRSS compare for twins and slip in Mg?
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
When is Mg mostly used for engineering applications?
When it is alloyed with other elements. Even though 99.8% purity readily available