Characteristics of primary phases in semi-solid A356 aluminum alloy was analyzed using multifractal theory

and the multi-fractal dimension spectrum was calculated.The results show that the primary phase in semi-solid A356 aluminum alloy exhibits multi-fractal characteristics.When helix angle in helical curve duct is 540°

the spectral width（Δα）of multi-fractal spectrum is the narrowest in the four groups of helix angle tests

and the distribution of primary phase is the most uniform.When pouring temperature is 635 ℃

the spectral width（Δα）of multi-fractal spectrum is the narrowest in the four groups of pouring temperature tests

and the distribution of primary phase is the most uniform and concentration.All morphology of spectral function f（α）is hooked to the left because of all spectral function symmetryΔfof eight group tests more than 0

and high probability subset is dominant.Parameters of multi-fractal dimension spectrum such as spectral widthΔα

spectral function symmetryΔfand spectrum function f（α）can be characterized by the quantificational dissimilarity of uniformity

which can describe the characteristics of semi-solid microstructure from a new point of view.