VALIDATION OF A SYSTEMATIC-APPROACH TO MODELING SPRAY QUENCHING OF ALUMINUM-ALLOY EXTRUSIONS, COMPOSITES, AND CONTINUOUS CASTINGS

Optimal cooling of aluminum alloys following the high-temperature extr usion process suppresses precipitation of intermetallic compounds and results in a part capable of possessing maximum strength and hardness after the subsequent age-hardening process. Rapid quenching suppresses precipitation but can lead to large spatial temperature gradients in complex-shaped parts, causing distortion, cracking, high residual stre ss, and/or nonuniform mechanical properties. Conversely, slow cooling significantly reduces or eliminates these undesirable conditions but a llows considerable precipitation, resulting in low strength, soft spot s, and/or low corrosion resistance. This study presents a systematic m ethod of locating and operating multiple spray nozzles for any shaped extrusion such that uniform, rapid cooling and superior mechanical and metallurgical properties are achieved. A spray nozzle data base was c ompiled by measuring the distribution of spray hydrodynamic parameters (volumetric spray flux, mean drop diameter, and mean drop velocity) t hroughout the spray field of various industrial nozzles. Spray heat tr ansfer correlations, which link the local spray hydrodynamic parameter s to the heat transfer rate in each of the boiling regimes experienced by the surface, defined the spatially nonuniform boundary conditions in a numerical model of the quenching process that also accounted for interference between adjacent spray fields, New correlations, offering increased accuracy and less computational time, were formulated for t he high-temperature boiling regimes which have a critical influence on final mechanical properties. The quench factor technique related pred icted thermal history to metallurgical transformations occurring withi n the extrusion to predict hardness distribution. The validity of this unique approach was demonstrated by comparing model predictions to th e temperature response (and hardness after artificial aging) of an L-s haped Al 2024-T6 extrusion to quenches with multiple, overlapping wate r sprays. The validation study reported herein concludes by exploring the possibility of applying quenching technology to improving the prop erties of extruded metal-matrix composites such as SiCp/Al 6061 and ca st alloys.