CLass notes

1. Grain Refining of Aluminum
Class 2: New metals in manufacturing

2. • Grain refining of aluminum is a process used to improve its mechanical properties,
castability, and surface finish by reducing the grain size during solidification.
• Finer grains enhance strength, ductility, machinability, and corrosion resistance.
Grain Refining of Aluminum

3. 1. Addition of Grain Refiners (Nucleation Control)
• Adding grain-refining agents introduces nucleation sites, which promote finer grain
structures. Common grain refiners include:
• Al-Ti-B (Aluminium-Titanium-Boron) Master Alloys
• Most widely used grain refiner.
• Titanium (Ti) forms TiAl₃ particles, while Boron (B) forms TiB₂ particles, both acting
as nucleation sites.
• Al-Ti-C (Aluminium-Titanium-Carbon) Master Alloys
Methods of Grain Refining in Aluminium

4. • Carbon (C) in the form of TiC improves grain refinement performance.
Used in high-performance casting applications.
• Al-Zr (Aluminium-Zirconium) Alloys
• Zirconium-based refiners provide long-lasting grain refinement at high
temperatures.
Used in aerospace and high-temperature aluminium alloys.
2. Rapid Solidification (Cooling Rate Control)
• Faster cooling during casting leads to finer grains because there is less time for
grain growth.
Methods of Grain Refining in Aluminium

5. • Techniques like die casting, electromagnetic stirring, and spray deposition enhance
grain refinement.
3. Ultrasonic Treatment
• High-frequency ultrasonic waves break up dendritic structures in molten
aluminium.
• This process promotes nucleation and reduces grain size.
• Used in advanced manufacturing for aerospace and automotive applications.
4. Mechanical Stirring & Electromagnetic Stirring
• Stirring the molten aluminium (mechanically or using electromagnetic fields)
disrupts grain growth and promotes fine grain structure.
Methods of Grain Refining in Aluminium

6. • Often combined with grain refiner additions for maximum effect.
5. Strain-Induced Grain Refinement (Thermo-Mechanical Processing)
• Rolling, extrusion, or forging breaks down coarse grains and refines the
microstructure.
• Severe Plastic Deformation (SPD) techniques like Equal Channel Angular Pressing
(ECAP) produce ultra-fine grains.
Methods of Grain Refining in Aluminium

7. ✔ Higher Strength & Toughness – Finer grains improve mechanical properties.
✔ Better Machinability & Weldability – Makes aluminium easier to process.
✔ Reduced Porosity & Cracking – Improves casting quality.
✔ Improved Corrosion Resistance – Smaller grains reduce localized corrosion.
✔ Better Surface Finish – Crucial for automotive and aerospace applications.
Advantages of Grain Refinement in Aluminium

8. Equal Channel Angular Pressing (ECAP) produce
Equal Channel Angular Pressing (ECAP) – A Grain Refinement Technique
• Equal Channel Angular Pressing (ECAP) is a severe plastic deformation (SPD)
technique used to refine the grain structure of metals, including aluminium
and magnesium.
• It enhances mechanical properties such as strength, hardness, and ductility by
producing ultra-fine grains (UFG) without changing the material’s shape.

9. Equal Channel Angular Pressing (ECAP) produce
How ECAP Works
1. Metal Billet Preparation
• A metallic billet (block or rod) is prepared and placed into a die with an L-
shaped or angular channel.
1. Severe Plastic Deformation
• The billet is forced through the angular channel under high pressure.
• The sharp bend (typically 90° to 120°) causes intense shear deformation,
breaking down coarse grains.

10. Equal Channel Angular Pressing (ECAP) produce
• This process is repeated multiple times to refine the grain size further.
• Microstructural Changes
• The process introduces dislocations and refines grains to the nano or sub-
micron level.
• After several passes, an ultra-fine-grained (UFG) structure is achieved.

11. Benefits of ECAP
✔ Significant Grain Refinement – Produces ultra-fine grains (as small as 100–500
nm).
✔ Increased Strength & Hardness – Due to the Hall-Petch effect (finer grains =
higher strength).
✔ Enhanced Ductility & Toughness – Unlike regular cold working, ECAP retains
good ductility.
✔ Improved Fatigue & Wear Resistance – Useful in aerospace, automotive, and
biomedical industries.
✔ Retained Original Shape – The billet keeps its initial shape, making it reusable
in further processing.

12. Applications of ECAP
• Aerospace & Automotive Components – High-strength aluminium and
magnesium alloys.
• Biomedical Implants – High-purity titanium and magnesium with better
biocompatibility.
• Electronics & Conductive Materials – Ultra-fine-grained copper and aluminium
for high-performance applications.