Sc. Lim et al., DECOMPOSITION KINETICS OF MACHINING OIL AND OXIDATION OF A356.2 ALUMINUM-ALLOY IN ALUMINUM RECYCLING PROCESS, Materials science and technology, 13(10), 1997, pp. 859-864
The recycling of scrap aluminium turnings or chips requires preprocess
ing steps such as thermal degreasing, drying, and removal of other met
al impurities on the surface of the scrap. The present study was perfo
rmed using a thermogravimetric technique to understand the decompositi
on kinetics of water-machining oil mixtures. The weight loss curves of
a water-machining oil mixture showed two distinct inflections over th
e temperature range studied (room temperature to 500 degrees C), with
a residue of oil still remaining at 500 degrees C. Oxidation kinetics
were studied and chemical analysis conducted of the oxide surface form
ed in both dry air and moist air for A356.2 aluminium alloy (Al-7 wt-%
Si-0.4 wt-%Mg) using a thermogravimetric technique and Auger electron
spectroscopy/X-ray diffraction respectively. The results showed differ
ent oxidation rate behaviour between oxidation in dry air and oxidatio
n in moist air at temperatures above 525 degrees C. That is, oxidation
in moist air showed a transition of parabolic to linear behaviour whi
ch was not observed for oxidation in dry air. Auger electron spectrosc
opy surface analysis and X-ray diffraction revealed that only aluminiu
m oxide was formed at 300 degrees C while a duplex film of MgO/Al2O3 f
ormed on the surface of the matrix at relatively high temperatures (55
0 degrees C). (C) 1997 The Institute of Materials.