Effects of the Addition of Si and Cu on the Chip Breaking under Lathe Machining of Al-1.0 mass%Mg-0.8 mass%Si Alloy

Abstract

For improving the machinability of aluminum alloys without adding low melting-temperature elements such as Pb or Bi, effects of the addition of Si and Cu, solely or in combination, on the chip breaking were examined for peak-aged (T8) Al-1.0 mass%Mg-0.8 mass%Si alloy (A 6061 alloy) under lathe machining at cutting speeds V = 0.83∼3.33 m/s in dry and wet atmospheres. The magnitude of chip breaking N = (the number of chips) / (100 g of chips) increased with a dcrease in V and with the addition of Si and Si+Cu in both cutting atmospheres. The value of N amounted to ∼22000/100 g, that is ∼6 times larger than that of 6061 alloy and is large enough for practical machining operation, at the smallest V of 0.83m/s in the wet atmosphere where the adhesion of work material on the tool surface scarcely occurred. Such a notable improvement of chip breaking by the combined addition of Si and Cu was ascribed to the existence of large Si particles at which micro-cracks appear and along which they propagate, and also to the solution and precipitation hardening of the matrix which results in the loss of fracture ductility.