Aluminium alloy inclusions

Here are examples of problems related to inclusions: In contact with ambient air, liquid aluminium reacts with the oxygen and form an oxide film layer (gamma-Al2O3).

Titanium boride (TiB2) is intentionally added to the melt for grain refinement to improve mechanical properties.

Phosphorus is added to the melt hypereutectic alloys for modification of the silicon phase for better mechanical properties.

Measuring the inclusions is of great help to understand the impact of furnace preparation, alloying practice, feedstock mix, settling time, and similar parameters on melt cleanliness.

It allows to quickly and accurately assess the effects of various operating practices on metal cleanliness or identify filtration efficiency.

The filter, along with the residual metal, is then cut, mounted and polished before being analyzed under an optical microscope by a trained PoDFA metallographer.

One can determine the cleanliness level from the filtration curve (weight of metal filtered as a function of time).

The visual observation of inclusions on the fracture is used to determine a K-value for the melt and compared to a preset standard.

[3] The LiMCA method[4] measures the total concentration and size distribution of inclusions present in aluminum alloys.

It can therefore monitor, in real-time, the evolution of cleanliness along a cast as a function of process parameters and melt-handling practices.

The heart of the LiMCA measuring system consists of a closed glass tube (electrically insulating material) bearing a small orifice at its bottom.

By creating a vacuum inside the tube, the metal with the suspended inclusions to be detected is forced through the small orifice.

When an inclusion enters the orifice, it displaces its volume of conducting fluid, temporarily raising the electrical resistance.