Modeling and optimization of cooling slope process parameters for semi-solid casting of A356 Al alloy

In the present work, semi-solid processing (SSP) of A356 aluminum alloy, via cooling slope (CS) method is discussed. The D-optimal design of experiment (DODE) was employed for experimental design and analyze 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° slope angles. Three different pouring temperatures of 660, 680 and 700 °C were also used. After the casting process, partial re-melting treatment was carried out at 590 °C for different isothermal times of 5, 8 and 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 dendritic primary 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.