Influence of anodisation on recycling of aluminium scrap

Abstract

The influence of anodisation on the recycling of a hitherto unknown Al-0.65Mg-0.5Cu-1.3Si-0.2Zn-0.03Fe (wt-%) scrap mixture has been fully ascertained. Aluminium scraps from aluminium processing industries (mill scrap) as well as scrap from obsolete, disused, and redundant, if not discarded, household and industrial goods were melted down and recast into predetermined shapes via the open loop recycling process. Standard spectrographic and electron optical techniques were used to ascertain the composition and structure of the said scrap entity whose corrosion and anodisation characteristics were effectively monitored and subsequently compared with the characteristic responses from superpure (99.99 wt-%) aluminium and binary Al-1.0Mg, Al-1.5Cu, Al-1.5Si, and Al-0.5Fe (wt-%) alloy standards. A characteristic linear response was generally exhibited during etching and on subsequent anodisation. However, some specimens markedly departed from the standard linear behaviour and were anomalous, a phenomenon not unconnected with high impurity concentration and hence, the relative effects of alloy segregation. Evidently, the Al- 0.65Mg - 0.5Cu -1.3Si- 0.2Zn- 0.03Fe specimen performed creditably and displayed no serious deleterious effects either during etching or on subsequent anodising. Its service performance was comparable with the superpure aluminium specimen and superior to both the binary Al-1.5Si and Al-0.5Fe standards and hence, it exhibits good recyclability and utility as high grade scrap. The various factors favouring or hindering the aluminium recycling process have been discussed.