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.

Effect of Homogenization Process on Microstructure of Al–Zn–Mg–Cu Aluminum Alloys

“…Compared with the H1 and H2 treatments samples, only Al 7 Cu 2 Fe and S(Al 2 CuMg) phases are observed in the H3 treatment sample, which means that σ [Mg(Zn, Al, Cu) 2 ] phase has dissolved completely after H3 treatment, whereas S(Al 2 CuMg) phase only has small amount. However, the investigation on influence of homogenization heat‐treatment and cooling modes on microstructure of AA7475 aluminum alloy ingot conducted by Reznik [ 24 ] is contradicting to our work. There may be two reasons for the discrepancies between these two studies, that is, on the one hand, high Cu content is reported to increase S(Al 2 CuMg) phase content remarkably; on the other hand, in our work, the holding time of 36 h was larger than the reported 24 h.…”

“…phase only has small amount. However, the investigation on influence of homogenization heat-treatment and cooling modes on microstructure of AA7475 aluminum alloy ingot conducted by Reznik [24] is contradicting to our work. There may be two reasons for the discrepancies between these two studies, that is, on the one hand, high Cu content is reported to increase S(Al 2 CuMg) phase content remarkably; on the other hand, in our work, the holding time of 36 h was larger than the reported 24 h. Furthermore, S(Al 2 CuMg) phase also disappears completely while only Al 7 Cu 2 Fe phase remains in the H4-, H5-, and H6-treatment samples.…”

“…Reznik [ 24 ] has also pointed out that Al 7 Cu 2 Fe phase still existed in the homogenized samples at 475 + 510 °C. The details for eliminating the residual coarse phase Al 7 Cu 2 Fe will be completed in our further work.…”

Numerical analysis of the non-stationary thermal state of the tool in the combined casting and extrusion of aluminum alloy

“…The development of technologies for foundry and metal forming is directed towards the unification of several technological stages in one installation [1][2][3][4][5][6][7][8]. These include, for example, a horizontal semi-continuous casting machine (HSCCM) [9].…”