Correlation between the microstructure and machinability in machining Al–(5–25) wt% Si alloys

Abstract

The machinability of the Al–Si alloys becomes worse with the Si content increasing. This article explored the influence of Si content on the machinability including cutting forces and chip breakability in machining the Al–Si alloys. The change in machinability of the Al–Si alloys with different Si content attributes to the evolution of microstructure. The cutting forces when cutting hypoeutectic Al–Si alloys are higher than the hypereutectic alloys because only Mg2Si ( β-phase) precipitations are formed in the former one versus cooperative precipitation of Al2Cu ( θ-phase) and Mg2Si in the latter. With regard to hypereutectic Al–Si alloys, cutting force components decrease with the increase in Si content due to the formation of brittle primary Si, which induces the initiation of cracks in material removal process. Moreover, the cutting stability of Al–Si alloys is improved with Si contents in the range of 12–18 wt%, while deteriorates for the Si content of 25 wt%. Besides, the chip breakability is improved due to the increase in eutectic silicon in hypoeutectic and eutectic ranges and because of the formation of block-shaped primary Si for hypereutectic alloys. The optimization of Si content is 12–18 wt% with cutting speed not less than 150 m/min.