Effect of copper on the tribological properties of Al-Si base alloys

Abstract

It is well established that rapid solidification of A1base alloys after processing powders, splats and ribbons through the powder metallurgy route of compaction followed by extrusion results in microstructural improvements, leading to improved properties [1-5]. It has even been possible to attain stability of the improved properties at elevated temperatures by adding intermetaltics, which precipitate out as dispersion strengthened phases [6, 7]. 350 Among the various alloy systems investigated, 325 hypereutectic A1-Si alloys have shown extension of 300 solid solubility beyond equilibrium limits up to the eutectic composition [8, 9] and improvements in 275 properties such as hardness, tensile strength and 25o mechanical properties in the consolidated and ~ 225 extruded product [2, 3, t0]. The A1-Si alloys are g zoo conventionally wear resistant alloys that find applica~ 175 tions as pistons and bearings. This letter reports an attempt to study the ~ 150 tribological properties of rapidly solidified and ~ 125 processed A1-Si base alloys, with and without ternary 1 oo additions. The effect of copper on the tribological 75 properties has been determined using X-ray diffrac5o tion (XRD). Conventional binary A1-Si alloys and alloys with 25 ternary addition of copper were prepared using 0 0 aluminium and solutes of 99.6% and 99.9% purity, (a) respectively. From these, conventionally prepared alloys, in batches of about 1 kg, were remelted at 1123 K in a resistance heating furnace and rapidly solidified to splats at a cooling rate of 105 Ks -1. The 3oo experimental details are given elsewhere [11]. Selected fractions of these splats were consolidated into billets of diameter 76 mm and extruded at 623 K 25o to rods of diameter 19 ram, at an extrusion rate of 16:t. Conventionally cast alloys of the same 2oo compositions were also extruded under the same "~ • g experimental conditions for comparison. The tribological properties of these alloys were _o 450 determined on a standard pin-on-disc set-up, in which cylindrical pins of diameter 8 mm were slid against a polished steel disc of hardness 30RC at loads 100 between 3 and 12 N. The wear rate was calculated from the slope of the steady rate wear region of the plot between weight loss and sliding distance. 5o Wear debris was collected and analysed using XRD for the alloy systems in both the rapidly 0 solidified extruded and conventionally cast extruded o conditions to assess the difference in the wear (b) behaviour. The chemical analyses of the conventionally cast and rapidly solidified alloys are given in Table I. It may be seen that there is no appreciable change in