The removal of transition metal impurities is essential in producing high-conductivity aluminium for wire and cable applications. Titanium, vanadium, chromium and zirconium and other elements – present in the metal as smelter impurities – significantly impede the electrical conductivity of aluminium. These solute impurities are generally precipitated from the melt through the addition of boron aluminium master alloys.
Boron Aluminium Treatments
Boron aluminium treatment is an environmentally safer and more cost-effective alternative to borax addition to electrolytic cells or potassium borofluoride (KBF4) treatment of aluminium in the mixing or holding furnace. Boron aluminium treatment avoids boron contamination of electrolytic cells, and eliminates KBF4 refractory attack.
How Boron Aluminium Treatment Works
After the addition of BAl (with an AlB2 or AlB12 microstructure), solute Ti, V and other impurities react with the aluminium borides, and these particles are precipitated, settling to the bottom of the melt to form a boride sludge. Clean, high conductivity Al is then decanted. Boron is trapped in the sludge at the bottom of the furnace. Adding boron in the launder in rod or cast form is an alternative, and less common treatment method. In this case, borides formed would be trapped in the filters. With either method, boron recovery should not be expected in the final alloy.
Boron Aluminium Additive
Concentrated boron aluminium additive achieves the same impurity removal efficiency as lower concentration alloys, but with a reduced boron unit cost. Boron aluminium lowers the cost of boron treatment in the casthouse, lessens material handling and reduces inventory.
Excessive boron from precipitation treatment can reduce the ability to grain refine. The controlled concentration, precise weight, individual piece identification and high metallurgical cleanliness ensure that boron levels are controlled, and high conductivity is achieved without compromising the desired grain structure in the cast alloy.
Benefits of Using Boron Aluminium Additive
• Cost-effective addition
• High concentration
• Same removal efficiency as lower-concentration alloys
• Ease of addition
• Precise weight
• Individual piece identification
• High metallurgical cleanliness
• Lower inventory costs
• Less packaging
Boron Aluminium must be added to the melt at the highest practical temperature, as early as possible before casting primary aluminium. Where boron additions are made in holding furnaces prior to casting, addition should be made at 720-750°C (1330-1380ºF), 30-120 minutes before casting. When boron aluminium is added as a trough addition (typically in rod or cast form) this may promote intermetallics in the final cast.
Original material sourced from Metallurg Aluminium