Wear behaviour of hypereutectic Al–Si–Cu–Mg casting alloys with variable Mg contents

Abstract

The wear properties of A390 (Al–17Si–4.5Cu–0.5Mg, wt%) hypereutectic Al–Si alloy were compared to new alloys containing 6 and 10 wt% Mg. The wear behaviour was investigated using dry sand rubber wheel (DSRW) abrasive wear apparatus for these alloys in the as-cast condition and after T6 heat treatment. A transformation of hard and coarse primary Si particles to fine Mg2Si particles with inferior hardness occurs with increasing Mg content. The finer particle size together with increasing solid fraction of the primary phase was found to be key factors in improving the wear resistance of alloys with high Mg content. In addition, the eutectic matrix microstructure of alloys with high Mg content showed considerable changes, particularly in size and morphology of the eutectic silicon which significantly contributes to the wear resistance. The wear test results showed improved wear resistance for alloys with high Mg content. The microstructure of the worn surface indicated that the intermetallic Mg2Si particles in alloys with 6% and 10% Mg addition are more solidly bonded to the matrix compared to the coarse primary silicon particles in A390 alloy which can be pulled out from the matrix. The worn surface of the A390 alloy exhibits deep and non-uniform grooves contrary to shallow and uniform grooves for the high Mg content alloys, resulting in the improved resistance to wear. Although the T6 heat treatment improved the wear behaviour of each alloy, the ranking of the wear property remained the same as the as-cast alloys.