Effects of heat treatment on the microstructural evolution and creep resistance of Elektron21 alloy and its nanocomposite


In previously published research, creep resistance of commercial alloy Elektron21 (El21) and El21 + 1% AlN/Al nanocomposite were predominantly investigated in as-cast condition, little work focused on creep resistance following heat treatment. In this work, El21 and its nanocomposite with and without T6 treatment (520 °C for 8 h and 200 °C for 16 h) were prepared to reveal the influence of heat treatment on their microstructural evolutions and creep properties. Different intermetallic particles and precipitates that formed in El21 and El21 + 1% AlN/Al with different states were characterized using optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). Creep tests were performed over a stress range of 80–140 MPa at 240 °C. Creep results showed that the application of T6 treatment could improve the creep resistance of El21, but deteriorate that of El21 + 1% AlN/Al. This is attributed to the reduced amount of γ'' and β′ precipitates in El21 + 1% AlN/Al (T6) after ageing, resulting from the formation of plate-like Al2(Nd, Gd) (Al2RE) precipitates. It is also found that after T6 heat treatment, El21 (T6) had a lower minimum creep rate with a shorter duration of secondary creep stage than El21 + 1% AlN/Al (T6) at high creep temperatures due to the overageing of precipitates and the thermal stability of the Al2RE particles. El21 + 1% AlN/Al nanocomposites, either in the as-cast or T6 condition, show a much longer duration of secondary creep than NP-free El21. The responsible mechanism was attributed to the addition of AlN NPs and the formation of particulate/plate Al2RE phase.
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