The removal of copper-phase segregation and the subsequent improvement in mechanical properties of cast 319 aluminium alloys by a two-stage solution heat treatment

Autor: D. E. Penrod, Xi-Chen Sun, Derek O. Northwood, G. Byczynski, J. H. Sokolowski, A. Esseltine, Romain Thomas
Rok vydání: 1995
Předmět:
Zdroj: Journal of Materials Processing Technology. 53:385-392
ISSN: 0924-0136
DOI: 10.1016/0924-0136(95)01995-q
Popis: The commercial heat treatment schedules that are utilized with cast AlSiCu alloys in order to obtain the optimum microstructure, and thereby optimum mechanical properties are often not effective because the precipitation strengthening process, which involves the precipitation of CuAl 2 or its precursors, does not occur in the desired manner since copper-rich phases, which form in the as-cast structure, are not fully dissolved in the aluminum solid solution during the solution treatment thus interfering with the desired precipitation on aging. Thermal analysis experiments for a 319 alloy show that the copper-rich phase in the as-cast alloy causes localized melting once the solution treatment temperature reaches 495°C, thus limiting single-stage (i.e., direct heating to temperature) solution treatment to temperatures of 495°C or below. To overcome these problems, a two-stage solution treatment has been developed for the 319 alloy where the conventional solution treatment is followed by a second solution treatment at a temperature above 495°C. Optical metallography showed that the two-stage solution treatment significantly reduces the amount of (as-cast) copper-rich phase in the alloy and gave rise to better homogenization prior to aging. Mechanical property measurements of cast alloys subjected to either the conventional or the two-stage solution treatments demonstrate the microstructural improvements generated by the two-stage process give rise to improve mechanical properties.
Databáze: OpenAIRE
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