Experimental and statistical investigation of changes in surface roughness associated with spray quenching

Surface contact profilometry data measured on aluminum surfaces were statistically analyzed to investigate the changes in surface roughness which occur during heal treatment. The tested samples included commercially pure aluminum (A1-1100) with polished, particle blasted, and milled finishes; and aluminum alloy A1-2024 with polished, particle blasted and extruded finishes. Statistical results along with scanning electron microscope photographs indicate each heat-quench cycle was accompanied by measurable changes in surface roughness, whose magnitude was dependent upon initial surface finish and alloy composition. The changes included both small scale roughness features, which influence cooling rate by increasing the number of bubble nucleation sites during transition and nucleate boiling, and, more importantly, large features which influence the impact and spreading of spray drops as well as the Leidenfrost temperature for spray quenching. The primary cause for roughness was determined to be a hydrogen diffusion phenomenon resulting from breakdown of water vapor al high temperatures inside moisture laden furnaces. Copyright (C) 1996 Elsevier Science Ltd.