Abstract: A burbling cooling technique used for preparing semi-solid alloys was presented.Water quenching specimens made of semi-solid AlSi9Mg alloy were prepared by which pin fins were put into a homemade sloping cooling device.The microstructures of the specimens were analyzed by the quantitative analysis technique.The influence of the shape,arrayed mode and arrayed pitch of pin fins on the microstructure of semi-solid AlSi9Mg alloy was studied.It is revealed that when the sectional shape of pin fins is water drop shaped,more α-Al phases with homogeneous microstructure and clear outline are obtained in the semi-solid alloy melt,showing spherical or nearly spherical shapes.The water quenching characteristics are the primary solid rate of 53.54%,the grain size of 5.59 μm and the shape factor of 0.61.Different arrayed modes and different arrayed pitches of pin fins have great influence on the microstructure of the semi-solid AlSi9Mg alloy melt.The cross array has more advantages over the order array under the same conditions,and the ideal spacing is the one with line spacing S=15 mm and column spacing L=40 mm.