ELEVATED TEMPERATURE DEFORMATION AND FORMING BEHAVIOUR OF AA7075 ALUMINUM SHEET MATERIAL

Abstract

Aluminum alloys are considered an attractive candidate in industry for automotive panels and structural parts for their high strength to weight ratio and consequently their higher potential for reduced fuel consumption and reduced carbon emission to environment. Wrought aluminum alloys from AA5xxx and AA6xxx series have been predominantly used in the manufacturing of automotive panels in the past. However, automotive industry is looking at aluminum alloys from AA7xxx series for further light weighting of automotive structural components. Specifically, AA7075 alloy has been of much interest especially in the context of hot stamping process since its room temperature formability is quite limited. This thesis aims at understanding the room and elevated temperature formability of automotive AA7075 sheet metal in different tempers (F, O and T6). Also, the relationship between formability, fracture, other mechanical properties, and microstructural and surface characteristics of this alloy are investigated in the low temperature range, 180°C- 260°C, in isothermal forming of this alloy. SEM-based microstructure studies for voidinduced damage and fractographic analysis as well as X-Ray diffraction (XRD) studies for analyzing undeformed and deformed grain orientation distribution (bulk texture) are carried out for different AA7075 sheet metal tempers. In addition, a study of development of surface roughness and material flow localization as a function of strain path and temperature is carried out. Lastly, two different strain rate and temperature dependent constitutive material models for AA7075 sheet are utilized in conjunction with the welliv known Marciniak-Kuczynski (or M-K) theory to predict the forming limits in the above experimental temperature range.