A parametric study of the relationship between microstructure and wear resistance of Al–Si alloys

Abstract

Wear tests were conducted on three commercial grade Al–Si alloys, a die cast 383 with 9.5 wt.% Si, a sand cast A390 with 18.5 wt.% Si and a spray cast alloy with 25 wt.% Si under dry sliding conditions. In addition, heat treatment processes were used to modify the microstructure and hardness of 383 alloy. This selection of materials and heat treatments provided a broad range of samples with different silicon weight percentage, morphology, size, and alloy hardness for comparison purposes. Using a method of pair-wise comparison, it was found that the effect of the individual contribution of each microstructural feature on the wear resistance could be isolated. Block-on-ring tests were performed under a controlled atmosphere of 5% relative humidity at a constant speed of 1 m/s. A mild to severe wear transition occurred at loads above 150 N irrespective of the alloy composition and microstructure. The mild wear regime consisted of two sub-regimes that were named as the first sub-regime of mild wear (MW-1) at low loads and the second sub-regime of mild wear (MW-2) at higher loads. The steady state wear rates ( W) in each sub-regime of the mild wear showed a power-law dependence to the applied load ( L) as W = CL n , where C is the wear coefficient, and n is the wear exponent. The wear coefficients, C 1 of MW-1 and C 2 of MW-2, and the transition loads L 1 and L 2, which denoted the start and end of the transition zone between MW-1 to MW-2, were sensitive to microstructure. Pair wise comparisons showed that an increase in the Si content from 9.5 to 25 wt.% increased the transition load L 1 by 140%, but had only a minor effect on C. An increase in alloy hardness from 31.6 to 53.5 kg/mm 2 provided a very significant increase in the transition loads (e.g., 400% increase in L 1), but did not have a notable effect on the values of C (only 3% increase). On the other hand, a decrease in the silicon particle aspect ratio from 3.75 to 1.98 increased L 1 by 25% and reduced C 1 by 25% (and C 2 by 31%). A decrease in the silicon particle size from 45.8 to 3.1 μm had the most significant effect on both wear parameters by reducing C 1 by 35% and C 2 by 58%, and increasing the transition load L 1 by 71%.