Directional migration of Sn in brass melt under pulsed electric current

The upgrading and recycling of scrap metal form the foundation of the circular economy; however, these processes are often hindered by the accumulation of harmful impurities that are difficult to remove. Brass recycling is particularly restricted due to tin contamination, which can cause embrittlement. Conventional refining methods are energy intensive and subject to environmental taxes, which often result in the loss of valuable volatile elements and the inseparable removal of Sn. Herein, a synergistic strategy combining targeted alloying with a pulsed electric current is demonstrated to actively sweep and remove impurity phases from a molten metal matrix. Application of a pulsed electric current to the Sn-contaminated brass melt induces the directional migration of native Cu 3 Sn intermetallic phases, achieving a purification efficiency of 25.3% at an optimal frequency of 1000 Hz. Notably, the purification efficiency is considerably enhanced to 60.9% at an optimal frequency of 100 Hz by pre-alloying the melt with Ca, which transforms the impurity into Ca 2 Sn phases, exhibiting a larger electrical conductivity difference with the brass melt. This frequency-dependent migration behavior is attributed to the force exerted by the current-density gradient on the induced dipole of the impurity phase, a phenomenon controlled by Maxwell–Wagner interfacial polarization. These findings establish a new physical principle for active melt purification and offer a scalable, efficient, and environmentally friendly alternative to traditional pyrometallurgy for refining various complex alloys.