Dislocation Breakaway Damping in AA7050 Alloy

Andrea Di Schino,Claudio Testani,Alessandra Varone,Roberto Montanari

doi:10.3390/met10121682

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.

Highlights

Thanks to their light weight, workability and relative low cost, the Al alloys are widely used for structural aeronautic applications [1,2,3]
In order to better understand the phenomena occurring during warm deformation of AA7050 alloy isothermal mechanical spectroscopy (MS) measurements have been performed at different temperatures, from room temperature to 185 ◦ C
The anelastic behavior of AA7050 alloy after the standard industrial hot-forging cycle has been investigated through isothermal MS tests carried out at temperatures up to 185 ◦ C

Summary

Introduction

Thanks to their light weight, workability and relative low cost, the Al alloys are widely used for structural aeronautic applications [1,2,3]. An innovative process, proposed by the present investigators [16,17], adopts an intermediate warm deformation step in the temperature range 150–200 ◦ C. This process improves fracture toughness without detrimental effects on yield stress and ultimate tensile strength. In order to better understand the phenomena occurring during warm deformation of AA7050 alloy isothermal mechanical spectroscopy (MS) measurements have been performed at different temperatures, from room temperature to 185 ◦ C. The MS technique is quite sensitive to the motion of lattice defects like dislocations, isothermal MS tests have been performed along a cycle with increasing and decreasing strain for investigating the mechanical behavior at strain levels well below those typical of the macroscopic plastic deformation

Materials and Methods

Results and Discussion

Conclusions