Industrial comminution of different Al scrap

Abstract

The comminution of different industrial scale Al scrap, namely Al bus bar plates, turnings and chips, was investigated for its potential as processing route to fabricate powders for the powder metallurgy (PM) supply chain. The proposed processing route included a roughening stage to pre-process coarse Al scrap followed by a comminution stage to generate a wide distribution of pulverized granules and powders. The roughening process effectively refined the size and microstructure of the scrap particles but it also induced Fe contamination of the feedstocks. Quantification of the exogenous contamination accumulated during storage prior to comminution amounted to 20.79±0.06wt% for the pre-treated plates, 8.47±0.05wt% for the pre-treated turnings and 0.54±0.02wt% for the chips. The comminution process of each feedstock was characterized by their residence time which controlled the particle size distribution, morphology as well as the extent of Fe, Mn and Si contamination. Upon screening, the powder fraction smaller than 106μm of each pulverized feedstock was characterized and exhibited a passivation layer thickness and Al2O3 dispersoids content of ~9.8nm and 15.34±0.23wt% Al2O3 for the pre-treated plates, ~9.5nm and 10.07±0.18wt% Al2O3 for the pre-treated turnings and ~6.8nm and 2.13±0.11wt% Al2O3 for the chips, respectively. In addition, the presence of nanoscale grains was highlighted within all pulverized powders. Ultimately, the pulverized powders prepared from each scrap feedstock were found suitable for the PM supply chain provided process improvements were achieved.