Strength variation of pre-strain aluminium alloys (axial compression) due to isochronal annealing

Aluminium-Magnesium (Al-Mg) alloys have very good formability
properties and have been used extensively for interior structural components of
automotive body-in-white (BIW). The alloys in an annealed temper attain their
strength through work hardening mechanism during press forming process. The
strengthening mechanism is due to Mg atoms in solid solutions exerting dislocation
drag during low temperature plastic straining. However, at elevated temperatures,
high diffusivity of Mg atoms allows easy dislocations rearrangements which lead to
reduction of mechanical strength (softening/thennal recovery). Furthermore,
accumulation of stored energy in the dislocations substructures due plastic straining
during press forming process also serves as a large driving force for thermal
recovery. The two factors caused the components made out of Al-Mg alloy sheet to
be susceptible to softening during paint bake cycle. This project will scientifically
analysis those factors and makes suggestions how to mitigate the problem.