Removal of Si from recycled aluminium alloys

Recycling of aluminium alloys is beneficial to the environment since it uses less energy than primary metal production. However, some instances, such as recycling of brazing sheets used for heat exchanger applications, lead to increased silicon content in Al–Mn alloys (3xxx series) due to the presence of clad layer of eutectic Al–Si alloy. In the present study, the removal of excess Si from recycled Al alloys has been investigated. The feasibility of removing silicon was evaluated using thermodynamic calculations. This was followed by some simple experiments by adding calcium to alloys with known silicon content to reduce it. It was found that the Si content can be reduced by 50% by this process.