An experimental investigation on the deformation and post-formed strength of heat-treatable aluminium alloys using different elevated temperature forming processes

Forming at elevated temperatures can significantly increase the ductility of aluminium alloys enabling the manufacture of complex-shaped panel components from sheets. This study describes and investigates two elevated temperature forming processes: Hot Form Quench (HFQ®) (Lin et al., 2008) and conventional hot forming (HF) of aluminium alloys, with various material condition and processing parameters in order to advance the understanding of forming characteristics and post-formed strength. High temperature uniaxial tensile tests of AA7075 under HFQ® and HF conditions were performed to compare the stress-strain behaviors, ductility, and post-formed hardness. The results have shown that the ductility for HFQ® condition was greater than that for the HF condition when forming temperature was below 400 °C. In addition, typical microstructural evolution, such as the low-melting phase of HFQ® and precipitation of HF, were identified using fracture morphology observations and used to explain ductility differences exhibited in these processes. Post-formed hardness resulting from HF with different initial alloy temper and forming conditions were determined and compared with those from HFQ®. Severe reduction in hardness was found for HF using both high quench-sensitive alloy AA7075 and low quench-sensitive alloy AA6082. For the first time, the effects of a variety of influencing factors are investigated systematically, including heating rate, initial alloy, temperature and strain rate, on the high temperature deformation and post-formed strength of heat-treatable aluminium alloys, which contributes to the thorough understanding of the correlation between forming conditions and microstructural evolutions.