High pressure die casting (HPDC) is an essential method for automotive, aviation and white good industry. Low cycle time due to fast solidification enables mass production. However, porosity and shrinkage are main failures that decreases efficiency. To prevent this, one of the solution is partial-solid casting. Casting in semi-solid phase affects the fluidity of the molten alloy and die filling. Dendritic microstructure turns into globular microstructure and it provides increase in yield and tensile strength, hardness and elongation at break. In this study, the factors affect the porosity ratio were determined as melt temperature, gas blowing time for producing partial-solid slurry, second phase velocity and gate thickness. L9 Taguchi method is used for process design and optimization of high pressure aluminum die casting. As responses porosity level and microstructural changes were determined. Microstructural, morphological and nondestructive testing were used in characterization. "A" class quality partial-solid aluminum automotive parts are successfully produced by Taguchi optimization.