Recrystallization resistance in aluminum alloys containing zirconium

Precipitation hardenable alloys of the 2XXX and 7XXX series have been in use in the aerospace industry since the 1920s. Some of the properties of interest in these alloys are strength, toughness, fatigue crack growth rate and resistance to stress corrosion cracking. These properties are influenced by the degree of recrystallization in the material. For example, the rate of loss in toughness with decreasing quench rate is substantially higher for recrystallized products. The degree or recrystallization is in turn influenced by the distribution and morphology of second phase particles that are formed in the microstructure.; In this study, the factors that influence the recrystallization behavior in aluminum alloys containing zirconium were investigated. Zirconium forms a fine dispersion of the metastable {dollar}betaspprime{dollar} (Al{dollar}sb3{dollar}Zr) phase that controls recrystallization by retarding the motion of high angle boundaries. The primary material chosen for this research was aluminum alloy 7150 containing zinc, magnesium and copper as the major solute elements and zirconium as the dispersoid forming element.; The size, distribution and the volume fraction of {dollar}betaspprime{dollar} was controlled by varying the alloy composition and preheat practices. Preheated ingots were subjected to a specific sequence of hot rolling operations to evaluate the resistance to recrystallization of the different microstructures. Optical and transmission electron microscopy (TEM) techniques were used to investigate the influence of dispersoid morphology resulting from the thermal treatments and deformation processing on the recrystallization behavior of the alloy. Studies were conducted to determine the influence of the individual solute elements present in 7150 on the precipitation of {dollar}betaspprime{dollar} and consequently on the recrystallization behavior of the material. These studies were done on compositional variants of commercial 7150, and to delineate the influence of the individual solute elements in 7150 on the precipitation of {dollar}betaspprime{dollar}, the deformation and recrystallization behavior of selected ternary and higher order alloys were also studied. The ternary alloys of interest contained each of the major solute elements in 7150 along with zirconium.