Effects of Cryogenic Treatment on the Microstructure and Residual Stress of 7075 Aluminum Alloy

The effect of cryogenic treatment (CT) on the microstructure, residual stress, and dimensional stability of 7075 aluminum alloy under temperatures of 0 degrees C, -60 degrees C, -120 degrees C, and -196 degrees C were studied, using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), an X-ray diffractometer, and an X-ray stress tester. The results indicated that CT can facilitate the dissolution of the coarse secondary phase into the alpha(Al) matrix, promote uniform distribution of Mg, Cu, Zn elements, and increase the density of fine secondary phases in the 7075 Al alloy. The CT can also induce the rotation of the alpha(Al) grain towards (200), through the processes of recovery and recrystallization. It was found that the residual stress was released, and a higher dimensional stability of the 7075 aluminum alloy was achieved, after CT. Experimental results demonstrated that the optimum CT temperature for the 7075 aluminum alloy is -120 degrees C.