Influence of Ageing Treatment on Microstructure and Properties of 7150 Alloy
The microstructure after different ageing treatments and its relation to the mechanical properties and corrosion behavior of 7150 alloy have been investigated. The microstructures were studied by optical microscopy (OM) and transmission electron microscopy (TEM). It was shown that suitable heat treatments led to a combination of high strength and corrosion resistance of the alloy. The yield strength of the alloy is 580MPa in peak aged state, which can be achieved by one step (120 °C/28h) or two step ageing (120°C/6h + 155°C/12h) tempers. The dominant matrix precipitates of the alloy for one step ageing temper are GP zones and η' phase. The alloy after ageing at 120°C for 28h is not susceptible to exfoliation corrosion. On the contrary, the alloy after two step ageing (120°C/6h + 155°C/12h) showed worse exfoliation corrosion resistance. The alloy exhibits high strength and good resistance to the exfoliation corrosion after the ageing treatment of 120°C/6h + 165°C/12h. The dominant precipitates within the grains are η' phase and η phase. The η phase at the grain boundaries plays an important role on the corrosion behaviors. The susceptibility of corrosion is associated with the potential difference between grain and grain boundary, and the characterization of grain boundary precipitates.
Yafang Han et al.
X. G. Fan et al., "Influence of Ageing Treatment on Microstructure and Properties of 7150 Alloy", Materials Science Forum, Vols. 546-549, pp. 849-854, 2007