When discussing the melting point relevant to aluminium welding, it's crucial to understand that two key temperatures are involved: the melting point of the aluminium itself and the melting point of its naturally occurring oxide layer.
The melting point of pure aluminium is approximately 660 C°. This is the temperature at which the base metal transitions from solid to liquid.
However, aluminium exposed to the atmosphere rapidly forms a thin surface layer of aluminium oxide. This oxide layer has a significantly higher melting temperature. According to the provided reference, the melting point of aluminium oxide is a striking 2072 C°.
This vast difference in melting points presents a major challenge in aluminium welding.
Why These Melting Points Matter in Aluminium Welding
The reference highlights a critical aspect of welding aluminium:
- Aluminium (Base Metal): Melts at 660 C°.
- Aluminium Oxide Layer: Melts at 2072 C°.
During the welding process, the base aluminium will melt and become fluid long before the surface oxide layer reaches its melting temperature. This means the molten aluminium can become trapped underneath the solid, high-melting-point oxide skin.
Challenges Posed by the Oxide Layer
Welding through this barrier can lead to several issues:
- Incomplete Fusion: The oxide can prevent the molten base metal and filler material from properly joining.
- Porosity: Trapped gases or breakdown of the oxide can create voids in the weld.
- Burning Through: As mentioned in the reference, trying to apply enough heat to melt or break through the oxide can easily cause the underlying aluminium to overheat and burn holes in the workpiece due to its much lower melting point.
Practical Solutions
To effectively weld aluminium, it's essential to manage or remove this stubborn oxide layer. Common techniques used in aluminium welding processes like TIG (Tungsten Inert Gas) or MIG (Metal Inert Gas) include:
- Cleaning: Physically or chemically removing the oxide layer before welding.
- AC Welding: Using Alternating Current (AC) in TIG welding helps "clean" the weld puddle. The reverse polarity phase of the AC cycle effectively blasts the oxide layer off the surface.
- Proper Shielding Gas: Using inert gases like argon protects the molten pool from atmospheric oxygen, preventing further oxide formation during welding.
Summary Table: Aluminium vs. Aluminium Oxide Melting Points
Understanding the difference is fundamental for successful aluminium welding.
| Material | Approximate Melting Point | Significance in Welding |
|---|---|---|
| Aluminium | 660 C° | Base metal melts here; target temperature for fusion. |
| Aluminium Oxide | 2072 C° | Surface layer; must be managed or removed for proper weld. |
In conclusion, while the aluminium base material melts at 660 C°, the much higher melting point of the surface oxide layer (2072 C°) is the primary obstacle that dictates the specific techniques and challenges encountered in aluminium welding.
