A comprehensive study on the effect of preageing temperature on formability characteristics of an Al-Mg-Si alloy

In the present work, finite element (FE) and digital image correlation (DIC) assisted mechanical tests were performed along uniaxial, plane strain and equi-biaxial strain paths to evaluate the formability characteristics of a preaged Al-Mg-Si alloy. A significant decrease in work hardening ability and strain rate sensitivity was observed with increasing preageing temperature, which in turn adversely affects formability parameters such as uniform and non-uniform elongation. Work hardening behavior along plane strain and biaxial strain paths was evaluated using crystal plasticity simulations and a similar trend of decreasing work hardening capability with increase in preageing temperature was observed. Fractographic analysis showed an increasing dominance of flat faceted regions over dimples and voids with increasing preageing temperature, suggesting that the fracture mode became less ductile with increasing preageing temperature. Microstructural analysis by TEM and EBSD revealed fewer occurrence of dislocation tangles and decrease in geometrically necessary dislocation density with increase in preageing temperature. The formability parameters were analyzed in combination with the strengthening response during the paint bake treatment (artificial aging at 180 degrees C for 30 min) to identify an optimized pre-ageing condition with good formability and excellent paint bake strengthening response.