Effects of artificial aging conditions on mechanical properties of gravity cast B356 aluminum alloy
(Department of Mechanical and Industrial Engineering, University of Brescia, Via Branze 38-25123 Brescia, Italy)
Abstract: The age hardening behavior of gravity cast B356 aluminum alloy was investigated by differential scanning calorimetry (DSC), hardness measurements and tensile tests. Three different artificial aging temperatures were selected, namely 155, 165 and 180 °C, with heat treatment time from 40 min to 32 h. 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 mechanical properties of the alloy. It was also confirmed that the hardness and the tensile properties of the alloy reach the maximum values when β'''''''' phase is completely developed during the artificial aging. This happens after 16 h for samples aged at 155 °C, after 6 h for samples aged at 165 °C and after 4 h 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 to be 57.2 kJ/mol.
Key words: B356 aluminum alloy; gravity casting; artificial aging; precipitation sequence; mechanical properties