Study on cooling contraction behavior of 7A09 aluminum alloy at different cooling rates

Alloy cooling contraction behavior has an important effect on accuracy and properties of hot processed parts. In this work, thermal simulation experiments were carried out, and with transmission electron microscopy and X-ray diffraction, the cooling contraction behavior of 7A09 aluminum alloy at different cooling rates was investigated. The results indicate that the precipitation of η phase (MgZn₂) is the predominant transformation in 7A09 alloy during the cooling process. The precipitation of η phase decreases cohesive energy of alloy and consequently causes the corresponding nonlinear change of thermal contraction coefficient (TCC). The amount of η phase decreases with the increasing of cooling rate, and TCC increases as the amount of η phase decreases.