Effects of Residual TiB2 and TiAl3 Nucleant on Grain-Refinement ofRecycled Aluminum-Silicon Alloy Castings

摘要

Recycling of return scraps is a general practice in aluminum foundries. These returnrnscraps were usually grain-refined using Al-5Ti-1B grain refiners in the previous process.rnAs a result, concentration of Ti and B can be found to be high even without any addition ofrnAl-5Ti-1B in the latter melt treatment. However, this high Ti and B contents may notrnnecessarily guarantee that the resultant melt will have an appropriate grain size. Thisrnresearch investigates the effectiveness of TiB2 and TiAl3 nucleant particles existing inrnreturn scraps previously grain-refined. The work was undertaken by recycling the grainrefinedrncastings for five cycles. Two silicon levels were tested: 6.7 and 9.5 wt. %. It wasrnfound that the concentration of both Ti and B gradually decreased by repeated use.rnHowever, the loss of grain refinement efficiency was found to be greater than the chemicalrnchanges, especially in the batch with higher Si content. It was suggested that presence ofrnhigh Ti and B contents in a returned scrap as a result of previous grain-refining does notrnguarantee fine grains in castings.