Microstructure Evolution and Recrystallization Resistance of a 7055 Alloy Fabricated by Spray Forming Technology and by Conventional Ingot Metallurgy

Abstract

The effect of different fabricating processes (spray forming and conventional casting) and homogenization treatment on the microstructure of an 7055 alloy was investigated by optical microscopy (OM), scanning electron microscopy (SEM), electron probe X-ray micro-analyzer (EPMA), and transmission electron microscopy (TEM). It was found that the grain size of the as-deposited (spray formed) 7055 alloy had half the size as that of the as-cast 7055 alloy and there was no Al 2 CuMg phase that embedded in the coarse Mg(Zn, Cu, Al) 2 phase distributed along the grain boundaries in the as-deposited 7055 alloy. No segregation of zirconium was observed in the as-deposited 7055 alloy. After homogenization heating at 350°C/5 hours + 470°C /24 hours, Al 3 Zr dispersoids were inhomogeneously distributed within grains in the traditionally cast 7055 alloy, while more homogeneously distributed within grains in the spray-formed 7055 alloy. Compared with the traditional cast 7055 alloy, the uniform distribution of Al 3 Zr dispersoids in the spray-formed 7055 alloy retards recrystallization more effectively. This investigation highlights the advantage of spray forming technology on improving microstructure of a 7055 alloy.

Regulate and Control Grain Structure Characteristics and Mechanical Properties Control of Al-Zn-Mg-Cu Alloy

“…When the alloy is deformed at low temperature, a large storage distortion energy is formed, which drives more vigorous dynamic recrystallization or static recrystallization. It can be seen from the literature that dynamic recrystallization of aluminum alloy is not easy to occur, so these recrystallized grains are likely to be formed by static recrystallization during solid solution heat treatment [7][8][9]. When the alloy is deformed at high temperature, the storage deformation energy is too low to drive static recrystallization, instead of dynamic recovery and static recovery.…”

Effect of Hot Deformation and Heat Treatment on the Microstructure and Properties of Spray-Formed Al-Zn-Mg-Cu Alloys

“…This approach resulted in superior mechanical properties, specifically, a yield strength of 608 MPa, a tensile strength of 667 MPa, and an elongation of 10%, respectively. Furthermore, Xie et al [9] found that due to the characteristics of the spray-forming process, compared with traditional cast Al-Zn-Mg-Cu alloys, the homogenization of spray-formed alloys will result in a more uniform distribution and smaller size of the Al 3 Zr dispersed phases, which better inhibits the occurrence of recrystallization. Figure 8 shows the grain structure after the hot extrusion of spray-formed and traditional cast 7055 aluminum alloys after homogenization.…”

“…It is generally accepted that the addition of 0.05-0.15 wt.% Zr can result in the formation of the fine intermetallic compound Al 3 Zr [134]. It was noted by Xie et al [9] that the distribution of Zr within the grain is uneven in the as-cast 7055 alloy, while it is uniformly distributed in the spray-formed 7055 alloy billet. This disparity results in differences in the precipitation behavior of Al 3 Zr after two-stage homogenization at 350 • C/5 h + 470 • C/24 h (at a heating rate of 30 • C/h).…”

“…Consequently, spray forming, a technique that has demonstrated clear advantages in producing ingots with fine grains, a uniform structure, and minimal oxidation, was introduced to fabricate high-alloying and high-strength aluminum alloys [6,7]. Over the recent decades, spray-formed Al-Zn-Mg-Cu alloys have undergone successful development and have been progressively commercialized [8][9][10]. To attain a better understanding of these alloys, an overview of their development history, associated hot deformation behavior, heat treatment, and precipitation behavior is provided in this paper.…”