Influence of Homogenization Heat Treatment and Cooling Modes on Microstructure of AA7475 Aluminum Alloy Ingot

Abstract:

Microstructure evolution during the homogenization heat treatment of an Al-Zn-Cu-Mg (AA7475, which is typically used for the manufacture of aircraft design) alloy, was investigated using a combination of light microscopy, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Ingots after different types (one-or two-steps treatments) of temperatures (from 380 to 510 °C) of homogenization and cooling conditions (cooling with an air or quenching to water) were investigated. The results show that the microstructure of ingot presents a typical microstructure with some isolated Al₇Cu₂Fe particles, which after homogenization almost remains in both the size and morphology. The structure ingot after homogenization below 400 °C contains secondary phases, based on η (MgZn₂), S (Al₂CuMg) and T (Al₂Mg₃Zn₃) are distributed along the grain boundary. In the T (Al₂Mg₃Zn₃) phase copper dissolves up to 30 wt.%. Then the increase in temperature and the complication of heat treatment of homogenization, which led to the complication of the kinetics of the evolution of inter-dendritic phases, were found. The two-steps homogenization has a better effect than a single homogenization, as its completely dissolution of non-equilibrium phases was established.

• Periodical: Materials Science Forum (Volume 989)
• Pages: 335-340
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.989.335
• Online since: May 2020
• Authors: Pavel L. Reznik*, Boris V. Ovsyannikov
• Keywords: 7475, Aluminum Alloy, Al-Zn-Mg-Cu, Differential Scanning Calorimetry (DSC), EPMA

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