Fabrication of CrSi₂-Containing Master Alloys for Modification of Fe-Containing Intermetallic Compounds in Aluminum Alloys

Aluminum contaminations, particularly iron, present a serious challenge to aluminum recycling technology. This is why many studies have focused on the reduction of detrimental effects of iron-containing contaminations through addition of elements such as manganese and chromium. However, the desirable modifying effect is often difficult to achieve because it would require concentrations of added elements greater than the allowable limits for many aluminum alloys. Thus, an alternative way to obtain the modifying effect, by using a much smaller amount of the modifying elements which are added to the aluminum melt as solid particles, was proposed in this study. The main goal of the present study was to investigate the possibilities of fabricating an aluminum master alloy by adding CrSi₂ particles onto the surface of the vortex formed during mechanical agitation of molten aluminum. Two kinds of CrSi₂ powder were used: one was commercial powder, and the other was self-synthesized CrSi₂ via mechanical alloying by planetary ball milling. The results revealed that CrSi₂ particles with a larger size penetrate the melt better. Particles of three kinds were found to exist in the Al melt after the addition of CrSi₂ powder: (1) inclusions of eutectic origin formed at the last stage of crystallization, (2) mixtures of Al-Cr compounds and original CrSi₂ particles and (3) original CrSi₂ particles. Low melt temperatures and short treatment times were found to favor the fabrication of master alloys because they impeded the dissolution of CrSi₂ particles into the Al melt and, thus, allowed one to fabricate the master alloy containing the particles of the second and third types.