Dislocation Breakaway Damping in AA7050 Alloy

Abstract

The AA7050 alloy prepared through the standard industrial hot-forging cycle has been investigated by means of isothermal mechanical spectroscopy (MS) from room temperature up to 185 °C. Each MS test consisted of a cycle with two stages, at increasing and decreasing strain. After each cycle the damping value resulted to be higher than the original one indicating the occurrence of an irreversible transformation. Such phenomenon, observed for all the test temperatures, becomes more relevant for T ≥ 150 °C. The irreversible transformation has been discussed and explained by considering the evolution of the mean dislocation link length between pinning points represented by nanometric MgZn2 precipitates. The breakaway of dislocation segments from pinning points occurs in the stage at increasing strain and is not fully recovered during the second stage at decreasing strain thus the mean link length increases in a MS test cycle. The onset of thermal activated dislocation cross-slip at about 150 °C favors the dislocation breakaway and consequently enhances the effect on damping.

Application of the Theory of Critical Distance (TCD) to the Breakage of Cardboard Cutting Blades in Al7075 Alloy

“…Following that, specimens were etched, and the micrographic and EDS analysis conducted in cross-section on a sample extracted near the fracture are reported respectively in Figures 10 and 11. The microstructure turned out to be homogeneous and compliant with a tempered Al7075 alloy [34][35][36][37], with Zn, Cu, and Mg precipitates homogeneously dispersed. In addition, segregation bands were not revealed.…”

Mechanical Spectroscopy Investigation of Defective Structures in Metals

“…MS has been extensively used by us to investigate several topics of metallurgical interest: structures of point defects and their effect on mechanical properties of Cr martensitic steels for nuclear fusion reactors [3][4][5][6][7][8][9][10][11][12][13], damping behaviour of Ti6Al4V+SiCf composite [14,15], structural stability of Ni base superalloys [16], microstructure evolution of FeAl B2-ordered alloy obtained by melt spinning [17], relaxation processes in high nitrogen austenitic stainless steels [18,19], damping of forged 7050 alloy [20], Young's modulus profile in kolsterized AISI 316 L steel [21], anelastic phenomena preceding the melting of metals [22] and accompanying structural transformations in the melts [23].…”