Abstract:Semi-solid processing (SSP) of A356 aluminum alloy was discussed via cooling slope (CS) method. The D-optimal design of experiment (DODE) was employed for experimental design and analysis of results. 38 random experiments obtained by software were carried out. In experimental stage, the molten aluminum alloy was poured on an inclined plate with different lengths of 100, 300 and 500 mm set at 30°, 45° and 60° of slope angles respectively. Three different pouring temperatures of 660, 680 and 700 °C were also used. After the casting process, the partial re-melting treatment was carried out at 590 °C for different isothermal time of 5, 8 or 12 min. The combined effect of these factors on globularity of the primary α(Al) crystals was investigated and optimized using DODE. The results indicated that the primary dendritic phase in the conventionally cast A356 alloy was transformed into a non-dendritic one in ingots cast over a cooling plate. The CS processed samples exhibited a globular structure only after re-heating to semi-solid region. The optimum values of pouring temperature, cooling length, slope angle and isothermal holding time were found to be 660 °C, 360 mm, 48°, and 9 min, respectively. In this case, the globularity of primary crystals was obtained, about 0.91. The obtained model is highly significant with a correlation coefficient of 0.9860.

Key words: A356 aluminum alloy; cooling slope process; modeling; D-optimal design of experiment