High power impulse magnetron sputtering (HiPIMS) technique was used to deposit AlSiN coatings on silicon Si (100) substrates using metallurgical Al0.8Si0.2 alloy target and under varying nitrogen-argon flow ratios from 5% to 50%. The current-voltage characteristics of the Al0.8Si0.2 alloy target was first investigated, and then the microstructure evolution and mechanical properties of AlSiN coatings grown with increasing nitrogen-argon flow ratios were analyzed by an x-ray photoelectron spectroscopy, grazing incident X-ray diffractometry, scanning electron microscope, transmission electron microscopy, and a nanoindenter. We found that the target was fully poisoned when the nitrogen-argon flow ratio was higher than 50%. The nitrogen-argon flow ratio plays a crucial role in the phase evolution. The phase changed from a metal-rich AlSi crystalline structure (nitrogen-argon flow ratio<10%) to a nanocomposites structure consisting of nanocrystalline c-AlN surrounded in the amorphous Si3N4 phase, which becomes more amorphous phase and smaller nanocrystalline as nitrogen-argon flow ratio increases. As a result, the hardness of AlSiN coating increased with increasing nitrogen-argon flow ratio, and reached a maximum value of 20.6GPa in this study.