Wear 261 (2006) 367–381 Progression of wear in the mild wear regime of an Al-18.5% Si (A390) alloy M. Elmadagli, A.T. Alpas ∗ NSERC/General Motors of Canada Industrial Research Chair in Tribology of Lightweight Materials, Department of Mechanical, Automotive and Materials Engineering, University of Windsor, 401 Sunset Avenue, Windsor, Ont., Canada N9B 3P4 Received 30 June 2005; received in revised form 8 November 2005; accepted 18 November 2005 Available online 18 January 2006 Abstract The mild wear regime of a cast Al-18.5% Si (A390), a lightweight alloy used in automotive components requiring wear resistance, was investigated in order to characterize the progression of the sliding wear processes. Block-on-ring (SAE 52100 steel) type sliding wear tests were conducted under a controlled dry air environment with 5% relative humidity. It was observed that the mild wear regime consisted of two sub-regimes: The first sub-regime of mild wear (MW-1) occurred at loads between 0.2 N and 35 N, and the second sub-regime of mild wear (MW-2) between 60 N and 150N. A common characteristic of MW-1 and MW-2 was the attainment of steady-state wear conditions. The load (L) dependence of the steady-state wear rates (W) in both sub-regimes was expressed as W = C(L) n , where C 1 = 1.08 × 10 -4 , n 1 = 0.56 for MW-1 and C 2 = 2.18 × 10 -4 , n 2 = 0.67 for MW-2. A transition regime, where the wear rates of MW-1 increased by 270%, occurred in the 35–60 N load range. The transition between MW-1 and MW-2 was accompanied by a rapid increase (25%) in the amount of material transferred to the counterface. Sliding wear in both sub-regimes proceeded by the formation of tribolayers that were initiated by iron transfer from the steel counterface to the silicon particles on the contact surfaces. Compared to MW-1, tribolayers were formed at a faster rate in MW-2 and the amount of material transferred to the counterface was larger. Also, in MW-2 the magnitudes of plastic strains (ε) in the deformed aluminum subsurfaces below the tribolayers were higher, e.g., at 40 m below the surface ε = 3 at 60 N, compared to ε = 0.1 at 10 N at the same depth. In addition, in MW-2, both the tribolayers and the material transferred to the counterface contained layers of aluminum, implying that the aluminum matrix became in contact with the counterface. Spallation of thick tribolayers formed in MW-2 as well as extrusion of exposed aluminum surfaces over the tribolayers were among the main reasons for the higher wear rates in this regime compared to MW-1. © 2005 Elsevier B.V. All rights reserved. Keywords: Al–Si alloys; Dry sliding; Wear mechanisms; Wear regimes; Tribolayers; Material transfer; Subsurface deformation 1. Introduction Because of their technological significance as lightweight alternatives to the traditional use of cast iron in automotive com- ponents, sliding wear behaviour of cast Al–Si alloys has been the subject of a large number of laboratory scale studies. Sarkar’s [1] work on a near eutectic Al-11% Si alloy and a hypereutectic Al-22% Si alloy tested against grey iron pins and the pin-on-disc tests by Shivanath et al. [2] on binary Al–Si alloy pins (4–20% Si) against steel discs (1% C–1.5% Cr) are among the early studies that have been often cited. These studies performed in late 1970s have shown that two distinct wear regimes occurred ∗ Corresponding author. Tel.: +1 519 253 3000x2602; fax: +1 519 973 7085. E-mail address: aalpas@uwindsor.ca (A.T. Alpas). during dry sliding of Al–Si alloys against iron based counter- faces, namely (i) a mild wear regime, which was characterized by low wear rates (10 -4 mm 3 /m to 10 -3 mm 3 /m) accompanied by formation of oxidized tribolayers on the contact surfaces and (ii) a severe wear regime that existed at high loads and test speeds, and was sometimes described as metallic wear due to the shiny appearance of severely deformed contact surfaces. The observations summarized by Eyre [3] are typical of these early studies. In the mild wear, the worn surfaces were covered by dark compacted oxide layers, presumed to consist of a mixture of aluminum oxide and some transferred iron. The severe wear was accompanied by the transfer of aluminum to the counter- face. Wear rates in the severe wear regime were usually one order of magnitude higher than those in the mild wear. Razavizadeh and Eyre [4,5] examined the oxidative wear mechanism during the sliding wear of Al-16% Si alloy pins tested against a steel 0043-1648/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2005.11.006