טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentKotler Hanna Shira
SubjectThe Influence of Thermo-Mechanical Treatments on the
Dynamic Strength and Failure Properties of
Selected Aluminum Alloys
DepartmentDepartment of Mechanical Engineering
Supervisors Professor Daniel Rittel
Dr. Lev Levin
Full Thesis textFull thesis text - English Version


Abstract

Aluminum alloys are widely used in protective structures due to their high strength-to-weight ratio. Metal forming (cold work) may affect the thermo-mechanical and failure response of materials. However, for the specific case of aluminum alloys subjected to dynamic loading, the exact influence of cold work on the mechanical response is relatively unknown, and thus remains to be assessed.

This research aims to identify and quantify the influence of cold work (either in the form of rolling or bending) on the dynamic mechanical properties of three different aluminum alloys, both in terms of flow strength and failure energy:

6061 and 7075:T4 and T6.

5083: annealed, H112 and H321,

Dynamic compression experiments (carried on a set of Split Hopkinson Pressure Bars (SHPB)) were conducted on Al 6061 and 7075 alloys in 3 main directions (2 for the 5083 alloy): rolling, longitudinal and transverse directions to characterize the basic dynamic properties and their level of anisotropy in the different treatments.

The main conclusions of the present study can be summarized as follows:

1.      Despite the anisotropy caused by the bending and rolling processes, the rolling and the longitudinal directions are almost identical with regards to the dynamic flow stress and microstructural grains geometry (elongated grains) for the three different alloys. On the other hand, the transverse direction (with almost equiaxed grains geometry) shows a relatively similar dynamic flow stress than the two others directions, together with a reduced ductility

2.      For the T6 condition, a homogeneous flow stress is obtained in the different directions and regions of the part (bent and flat) for both Aluminum 7075 and 6061 alloys (despite the anisotropic microstructure).

3.      Aluminum 5083 can be considered as strain rate insensitive: the overall strain rate sensitivity is essentially expressed by a reduction of the strain hardening in the dynamic regime.

4.      For Al 5083 the dynamic failure energy remains constant over a wide range of strain rates with the different levels of pre-strain (0%, 10% and 20%), and in the two different directions (rolling and longitudinal direction).

5.      For Al7075 and 5083, failure occurs by adiabatic shear (independently of the direction and the condition). This tendency was not observed for Al6061 alloy.