Lecture 6 - Aluminum Alloys Flashcards
What is the crystal structure of pure Al?
FCC
What is the melting point of pure Al?
660.2C
What is the boiling point of pure Al?
2480C
What is the mean specific heat for pure Al?
.219 cal/gC
What is the thermal conductivity for pure Al?
.57cal/cms*C
What is the co-efficient of linear expansion for pure Al?
23.5 x10^-6/C
What is the electrical resistivity for pure Al?
2.69 ohm*cm
What is the modulus of elasticity for pure Al?
68.3 GPa
What is the Poissons Ratio for pure Al?
0.34
Al is _______ than Cu. Coarse-grained Al is one of the __________materials in the world.
softer
Al has the ______________________________ among all FCC metals
highest stacking fault energy
What are the two major categories of Al alloys?
cast and wrought
What are five properties of cast AL alloys?
high alloy content 8-12 wt %
cast-to-shape
little heat treatment
low mechanical properties (120-300 MPa UTS, strain 5%)
cheap
What are five properties of wrought Al alloys?
low alloy content 1-3%
made into standardized products (sheets, rods, bars, tubes)
extensive heat treatment, solutionizing, aging
550 MPa UTS, strain 5-20%
wide-range of applications
What are five common issues to printing aluminum alloys in L-PBF (wrought)?
low laser absorptivity (minor due to low melting temp)
Al is prone to oxidation
high residual stress
hot cracking (solidification cracking, hot-tearing)
composition control
How does hot cracking occur?
contraction of solid phase and liquid phase in large semi-solid zone specific to wrought Al alloys produces poor fluidity
Why are cast Al alloys not susceptible to hot cracking?
low solidification shrinkage, high fluidity, easy to print
Why are wrought Al alloys susceptible to hot cracking?
large solidification shrinkage, large semi-solid zone, difficult to print
How does Si affect Al?
Si helps form cellular structures but produces poor elongation
How can hot cracking be mitigated?
decorate with nanoparticles, but change solidification behavior
What do current Al alloy print studies focus on?
printability
What do nanoparticles do to Al alloys?
enhance printability and mechanical properties (not sure about corrosion resistance)
Why is 3D printing not the best approach for Al?
not high value products (cheap)
What does high stacking energy mean?
no twinning
Which Al series is interested in 3D printing?
7000 series
Which Al alloy is popular for L-PBF?
Al-Si-Mg
Why is composition difficult to control?
Evaporation of other materials (Zn, Mg)
