Aluminum and Aluminum Alloys Notes

General Characteristics:
- Good corrosion and oxidation resistance.
- High electrical and thermal conductivities.
- High ductility and medium strength.
- Low density: Aluminum has a density of 2.7 g/cm^3, while steel has a density of 7.8 g/cm^3.
- Second only to steel in engineering applications.
Applications:
- Containers and packaging (e.g., pods, foils, beverage cans).
- Structural materials in architecture and transportation (e.g., aircrafts, automobiles, bicycles).
- Electrical applications (e.g., Al wires, copper-clad Al wires).
- Radiators and cooking utensils.

Cast Alloys
- Manufactured by casting into shape.
- Formulated for good casting properties, such as fluidity and flow.
- Can be heat treatable or non-heat treatable.
Wrought Alloys
- Manufactured using a forming technique after initial casting.
- Includes sheets, foils, extrusions, wires, rods, etc.
- Can be heat treatable or non-heat treatable.
Four-Digit Designation System (Aluminum Association)
- Used for both wrought and cast aluminum alloys.
- For cast alloys, a decimal point is incorporated.
  - The number after the decimal is 0 for cast products and 1 for ingot.
  - A serial letter precedes the numerical designation to indicate higher purity level (e.g., A357.0).
Examples
- Wrought: 2011, 1100, 2014, 3003, 2017, 3004, 2018, 5005, 2024, 5050, 4032, 5052, 6061, 5083, 6062, 5086, 6063, 5456, 6151, 7075, 7079, 7178
- Cast: 213.0, 208.0, 222.0, 360.0, A360.0, 308.0, 380.0, 413.0, 295.0, 355.0, 356.0

F - As Fabricated
O - Annealed
H - Work-Hardened (HXX)
- H1X - Cold worked only.
- H2X - Cold worked and partially annealed.
- H3X - Cold worked and stabilized.
- HX2 – ¼ hard, HX4 – ½ hard, HX6 – ¾ hard, HX8 - Hard, HX9 – Extra hard
W - Solution Heat Treated
T - Heat-Treated (TX) with residual hardening

T1 – Cooled from fabrication temperature and naturally aged.
T2 – Cooled from fabrication temperature, cold worked, and naturally aged.
T3 – Solution-treated, cold-worked, and naturally aged.
T4 – Solution-treated and naturally aged.
T5 – Cooled from fabrication temperature and artificially aged.
T6 – Solution-treated and artificially aged.
T7 – Solution-treated and stabilized by overaging.
T8 – Solution-treated, cold-worked, and artificially aged.
T9 – Solution-treated, artificially aged, and cold worked.
T10 – Cooled from fabrication temperature, cold worked, and artificially aged.

Function: Reduces or eliminates internal stresses from manufacturing processes.
- Reduces warpage during machining.
- Improves fatigue and stress-corrosion resistance.
Designations:
- Tx51: Stretch in tension.
- Tx52: Compression.
- Tx54: Combination of tension and compression.

Solid Solution Strengthening
- Solution heat treated (W).
Dispersion Strengthening (micron-scale particles)
Precipitation Strengthening (nano-scale particles)
- Solution heat treated and aged (T).
Strain Hardening
- Various work hardening (H).

Source: Strain field interferes with dislocation movement.
Magnitude depends on:
- Atom size difference (interstitial or substitutional).
- Percentage of solutes.
Problem caused: Natural aging.
Types
- Interstitial atom
- Substitutional atom

Heat treatments:
- Solutionizing followed by quenching and artificial aging.
Aging conditions: Temperature and time.
Typical precipitation sequence:
- Super saturated solid solution → Clustering → GP zones → θ" → θ' → θ
Effective precipitates:
- Small, hard, round, and in large amounts.
- Coherent or incoherent with the matrix.
- Great matrix alignment and lattice strain.
Strengthening Mechanism: Interaction between precipitates and dislocations
- Bowing/Looping (incoherent precipitates).
- Shearing/Cutting (coherent precipitates).
Hardening effect depends on:
- The volume fraction.
- The interspacing.
- The type.

Background
- Strain hardening achieved through processes like rolling, drawing, forging, and extrusion which Increase the strength.
- Both cold and hot working involved.
Deformed structure
- Deformed grains and preferred orientation.
Issues with strain hardening
- Becomes harder to process due to high strength and low ductility.
- Internal residual stress leads to crack propagation and stress corrosion cracking.

Annealing
- High temperature, but below solutionizing temperature.
- Removes internal stress and preferred orientation, increases ductility, and forms new grains.
- Involves recovery, recrystallization, and grain growth.

Definition
- Replacement of deformed cold-worked grains by new strain-free grains.
- Solid-solid transformation.
- Grain reforming and precipitation (for some materials).
Driving force (ΔH)
- Stored energy from work hardening.
- Thermodynamically unstable.
Thermal energy
- Short-range diffusion.
- Activation energy (E_a) for diffusion.
Recrystallized Temperature
- Recrystallization takes place in a range, depending on composition and amount of cold work.
- Recrystallization temperature (T_R): 50% recrystallization in 30 min or 100% recrystallization in 1 hr.
- Proportional to the melting point (range from 0.3 - 0.5 of melting temperature).

Shear bands are inclined by about 35-40 degrees with respect to the rolling direction (RD).

Localized strain concentrations at particle-matrix interfaces.
Particle stimulated nucleation mechanism (PSN).
Pre-existed particles
- Large particles (>1 µm)
- Small particles
- Deformation zones
- Particle simulated nucleation(PSN)

A dispersion of precipitates retard the motion of a grain boundary
For a random distribution of particles, the pinning force (Pz) exerted on the boundary is given by: Pz = \frac{3f\gamma_b}{2r}
- where f and r are volume fraction and radius of the particle
- γ_b denotes the energy of grain boundaries

TEM
Hardness measurement
Electronic backscattered diffraction analysis (EBSD)
- Orientation map
- Grain boundary map
- Texture characterization