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TECHNICAL PAPERS

An Experimental Investigation Into the Relationship Between Temperature-Time History and Surface Roughness in the Spray Quenching of Aluminum Parts

[+] Author and Article Information
John D. Bernardin, Issam Mudawar

Boiling and Two-Phase Flow Laboratory, School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907

J. Eng. Mater. Technol 118(1), 127-134 (Jan 01, 1996) (8 pages) doi:10.1115/1.2805925 History: Received June 07, 1994; Revised March 03, 1995; Online November 27, 2007

Abstract

Repeated heat-quench cycles of Al-1100 samples resulted in increased surface roughness and corresponding shifts in the temperature-time cooling curve towards shorter overall quench periods. Three different types of initial surface roughness were applied to the test samples: polished, particle blasted, and milled finishes. For each of the three test surfaces, cooling curve shifts during repeated heat-quench cycles were accompanied by surface roughening, the shift was smallest with the milled sample. The surface roughness was examined with the aid of scanning electron microscopy, surface contact profilometry, and X-ray photoelectron spectroscopy. Surface profiles obtained via the profilometer revealed, on a relative basis, significant changes in surface roughness on the polished and particle blasted surfaces but not on the milled (roughest) surface. The roughening was the result of (a) hydrogen diffusion associated with oxidation, (b) oxidation buildup, and, to a lesser extent, (c) expulsion of impurities along dendrite boundaries. The hydrogen diffusion caused localized pressure buildup within the surface and along grain boundaries resulting in the formation of both microscopic (1 to 10 μm) features on the polished and particle blasted surfaces and relatively large (20 to 1000 μm) bumps and blisters on the particle blasted surface. It is shown how these wide spectrum surface roughness features affect cooling rate by (a) raising the Leidenfrost temperature separating the film and transition boiling regimes, (b) increasing the number of boiling sites on the quenched surface, and (c) altering the impact dynamics of the spray drops.

Copyright © 1996 by The American Society of Mechanical Engineers
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