The dimensional stability of the cast W319 aluminum alloy in the T4 ('naturally-aged'), T6 ('peak-aged') and T7 (overaged') heat-treated conditions was studied by exposing heat-treated samples temperatures of 100 deg C, 180 deg C, and 250 deg C for times up to 1000 hours. The results show that the T7 heat-treatment provides a dimensionally stable microstructure for all three of the exposure temperatures. The T4 and T6 heat-treatments are only dimensionally stable for times less than 1000 hours at 100 deg C; at 180 and 250 deg C, significant thermal growth (up to 0.09 %) can occure at times as short as 10 hours. The thermal growth in the W319 alloy is attributed to changes in the precipitate type and morphology. In general, the transformation to and from the teta' precipitate phase involves a change in volume on an atomic level that can, under certain conditions, manifest itself as a change in dimension. This range in precipitate type and morphology is also responsible for the differences observed in the mechanical properties of the heat-treated W319 alloy. In certain conditions, changes in the secondary dendrite arm spacing (40 micron vs. 80 micron) were found to have a modest effect upon the resulting amount of thermal growth in the heat-treated W319 specimens. To understand the importance of thermal growth, the dimensional changes resulting from thermal growth were compared to those arising from thermal expansion. Thermal growth was found to be minor (<10 %) compared the thermal expansion for the W319-T7 samples and for all W319 heat-treted samples exposed at 100 deg C. For the W319-T4 samples exposed at 180 deg C and 250 deg C as well as the W319-T6 samples at 180 deg C, thermal growth was found to increase the dimensional change up to 24 % over that arising from thermal expansion. This highlights the need for understanding the effects of thermal growth in high-precision, high-tolerance cast aluminum components.
The dimensional stability of cast 319 aluminum
Die Maßstabilität der Aluminiumgusslegierung 319
2003
11 Seiten, 19 Bilder, 3 Tabellen, 11 Quellen
Aufsatz (Konferenz)
Englisch
The Dimensional Stability of Cast 319 Aluminum
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