This paper aims to investigate and compare the characteristics of machined surfaces and chips formation of aluminium-based automotive alloys with varying silicon content. The milling operations are performed using horizontal milling machine under two peripheral up milling and down milling methods with an HSS slab milling cutter. The experiment has conducted for different cutting speeds in dry condition while the depth of cut and machining feed are kept constant throughout the evaluation. The study reveals that the down-milled surface has higher hardness and better surface finish resulting in lower roughness as the cutting force is compressive in nature. On the contrary, the up-milled surface has lower hardness and micro cracks on it, which resulted in relatively higher surface roughness as the cutting force is tensile shear in nature. In addition, the surface hardness increases with the increment of silicon content in the alloys for both milling methods for the presence of hard Si rich intermetallics. The chips produced during up milling are shorter whereas the chips produced during down milling are longer for creation of higher temperature and pressure. Higher Si added alloy shows the curly like chips for its lower elongation behaviour. Fracture behaviour of higher Si alloy also confirms crack propagation obtained by the massive cleavage of the brittle and plate-types Si rich intermetallics.