Scripta METALLURGICA Vol. 28, pp. 91-96, 1993 Pergamon Press Ltd. et MATERIALIA Printed in the U.S.A. All rights reserved DAMPING BEHAVIOR OF PARTICULATE REINFORCED 2519 AI METAL MATRIX COMPOSITES J. Zhang, R.J. Perez, M. Gupta and E.J. Lavemia Materials Science and Engineering Department of Mechanical and Aerospace Engineering University of California, Irvine, CA 92717 (Received October 28, 1992) The development of 2519 AI alloy (Al-Cu-Mg-Mn) was prompted by the need to achieve excellent strength and ballistic performance, as well as adequate stress corrosion cracking resistance [1]. In a recent study by Gupta et al. [2], the physical properties of 2519 AI alloy were further modified through the addition of SiC and A1203 particulates. An important characteristic of the resultant metal matrix composites (MMCs) which was not explored, however, was the damping capacity. This is of interest in light of recent work [3] which suggests that the presence of ceramic particulate influences damping behavior. Material damping refers to the dissipation of energy to the surrounding environment by a reversible microstructural movement or an irreversible thermoelastic process inside the material during mechanical vibration [4]. When a high damping material is effectively utilized in a structure exposed to a dynamic environment, this property allows undesirable noise and vibration to be passively attenuated. Hence, the application of high damping materials may eliminate the need for special energy absorbers or dampers. 2519 AI is essentially an AI-Cu alloy. Inspection of the relevant scientific literature shows that studies on the damping or internal friction of AI-Cu alloys began with the work of Berry and Nowick on an AI-4wt.%Cu alloy [5]. They investigated the damping behavior of this alloy under different aging conditions and observed a damping peak associated with the semicoherent 0' phase (transitional Cu-rich particulates). The transitional phase will transform to a stable incoherent 0 phase (A12Cu) when the specimen is aged further at elevated temperatures. In related studies, Cui and K6 [6] attributed the damping peak behavior of A1-4wt.%Cu at approximately 400°C to the presence of the 0 phase. On the basis of these studies, it is well established that AI-4wt.%Cu is essentially a low damping material, even though the presence of the stable 0 phase increases the internal friction background and peak values. In view of the above findings, the present study was undertaken with the two primary objectives. First, the present work sought to characterize the damping behavior of spray atomized and co-deposited 2519 A1 MMCs. Second, the present study was completed to provide insight into the operative damping mechanisms that were active in these types of MMCs. The selection of spray atomization and deposition processing was prompted by recent interest in this technique to synthesize discontinuously reinforced MMCs [7-9]. Accordingly, three types of ceramic particulates, i.e., SiC, A1203 and graphite, were used as reinforcements to investigate their effect on the resultant damping and modulus of the MMCs. Damping measurements were conducted on a dynamic mechanical thermal analyzer (DMTA) at 0.1, 1, 10 and 30 Hz over the temperature range of 30-500°C. The intrinsic damping mechanisms in the MMCs were discussed on the basis of microstructural studies. 2, Experimental The 2519 AI alloy was provided in the form of rolled plates by the Army Materials Technology Laboratory (Watertown, MA). The nominal composition of the alloy is: 5.0-7.0% Cu, 0.1-0.3% Mg, 0.0-0.8% Mn, 0.0-0.1% Ti, 0.0-0.25% V, 0.0-0.25% Zr, 0.0-0.5% Fe, 0.0-0.5% Si, 0.0-0.12% Zn and the balance in AI (in weight percent). The ceramic reinforcements were a-1200 SiC, ¢t-A1203and 2922 flake crystalline graphite (2922 Gr) particulates; the latter was supplied by the Superior Graphite Co. (Chicago, IL). Table 1 lists the relevant physical data of the matrix and reinforcements at ambient temperature. In this table, ds0 denotes the average particulate size, p the density, E the modulus, tan, the loss tangent representing material damping capacity, and CTE the coefficient of thermal expansion. The particulate reinforced 2519 MMCs were synthesized by spray atomization and deposition, referred to hereafter as spray processing. A detailed description of this synthesis methodology may be found elsewhere [7-9]. In addition to 91 0956-716X/93 $5.00 + .00 Copyright (c) 1992 Pergamon Press Ltd.