Materials Science and Engineering A 478 (2008) 251–256 Dimensional behaviour of aluminium sintered in different atmospheres T. Pieczonka a , Th. Schubert b,∗ , S. Baunack c , B. Kieback b a AGH University of Science and Technology, Mickiewicza 30, 30-059 Kracow, Poland b Fraunhofer-Institute for Manufacturing and Advanced Materials, Department of Powder Metallurgy and Composite Materials, Winterbergstr. 28, D-01277 Dresden, Germany c IFW Dresden, Leibniz-Institut f¨ ur Festk¨ orper- und Werkstoffforschung Dresden, Postfach 270116, D-01171 Dresden, Germany Received 26 January 2007; received in revised form 30 May 2007; accepted 1 June 2007 Abstract The sinterability of pure aluminium powder was controlled in different sintering atmospheres, i.e. nitrogen, argon, nitrogen/hydrogen and nitro- gen/argon gas mixtures, and also in vacuum. Dimensional changes occurring during sintering were monitored by dilatometry. Thermogravimetric analysis (TG) was used to recognize possible interactions between aluminium and nitrogen. Pure nitrogen was found to be the only active sintering atmosphere for aluminium, promoting shrinkage, associated with a weight gain by binding nitrogen, and enhancing mechanical properties of the sintered compacts. Hydrogen lowers the sinterability of aluminium very strongly, even when present in small concentrations in a nitrogen atmosphere. Auger electron spectroscopy was used to characterize the surface layers on aluminium powder particles, fractured green compacts and sintered samples. Distributions of aluminium, nitrogen, oxygen and other elements, contained as impurities, were obtained by depth profiling measurements on this surfaces. Indications are that enhanced concentration of magnesium within the powder particle surface film promotes sintering of aluminium. © 2007 Elsevier B.V. All rights reserved. Keywords: Sintering of aluminium; Sintering atmosphere; Dilatometry; AES 1. Introduction During the last decade, interest in sintered aluminium-based structural parts for the automobile industry has dramatically increased [1], as evidenced by the number of scientific papers and successful use-oriented developments. Prospective conven- tional press-and-sinter aluminium components include camshaft bearing caps and the rotor and sprocket for a camphaser system. Industrial development of aluminium powder technology is impeded by the very stable Al 2 O 3 layer on powder particles, which cannot be reduced during conventional sintering. Suc- cessful sintering of aluminium alloys can only be achieved through the formation of a liquid phase—able to disrupt the stable oxide skins [2]. Copper is a well-known alloying element for liquid phase activation [3,4]. An important processing fac- tor, more complex, as compared with, e.g. iron, is the sintering atmosphere. The best-sintered properties of aluminium-based compacts are achieved by sintering in dry nitrogen, mostly ∗ Corresponding author. Tel.: +49 351 2537 346; fax: +49 351 2537 399. E-mail address: Thomas.Schubert@ifam-dd.fraunhofer.de (Th. Schubert). evaporated liquid nitrogen [5–10]. The interactions between aluminium-based compacts and the sintering atmosphere have been analysed, but unanswered questions remain, one of which is the role of hydrogen. Some researchers claim that hydrogen had little influence [11], while various investigations have shown that it had a detrimental effect on sintering of aluminium and its alloys [5,12–16], because it strongly reduces the sintering shrinkage. The main purpose of this work was to investigate the influence of the sintering atmosphere on the dimensional changes of pure aluminium compacts during solid state sinter- ing. High purity aluminium powders were used to eliminate the effect of alloying additions and a liquid phase on the sintering behaviour. 2. Experimental procedure The raw material was an air atomized, 99.5% purity alu- minium powder, delivered by Fluka (impurities: Si, 0.15; Fe, 0.15; Mg, 0.02; Cu, 0.03 wt.%; particle size: 28% <20 m/23% 20–40 m/49% >40 m). For dilatometry investigations rectangular (14 mm × 4 mm × 4 mm) green compacts were produced by uniaxial cold press- 0921-5093/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2007.06.002