Effects of Artificial Aging Conditions on the Mechanical Properties of Gravity Cast B356 Aluminum Alloy

The age hardening behavior of gravity cast B356 aluminum alloy was investigated by means of differential scanning calorimetry (DSC), hardness measurements and tensile tests. Three different artificial aging temperatures were selected, namely 155°C, 165°C and 180°C, with heat treatment times from 40 minutes to 32 hours. DSC analysis results show that cluster formation begins below room temperature (at around -10°C). Since cluster formation influences the subsequent precipitation of the main strengthening β'' phase, it can be inferred that a delay between solutionizing and artificial aging has a detrimental effect on the alloy’s mechanical properties. It was also confirmed that the hardness and the tensile properties of the alloy reach the maximum value when β'' phase is completely developed during the artificial aging. This happens after 16 hours for samples aged at 155°C, after 6 hours for samples aged at 165°C and after 4 hours for samples aged at 180°C. A subsequent decrease of the mechanical properties, observed only in the sample aged at the highest temperature, with increasing aging time can be associated with the transformation of the coherent β'' phase into the semi-coherent β' phase. Finally, the activation energy associated with the precipitation of β'' phase was calculated (57.2kJ/mol)