Effect of Zr on the high cycle fatigue and mechanical properties of Al–Si–Cu–Mg alloys at elevated temperatures

Abstract

The Zr-modified Al–Si–Cu–Mg alloy with 0.14 wt%Zr addition was studied against the counterparts of commercially used EN-AC-42000 (Al7Si0.5Cu) baseline alloy for the effect of Zr on the high cycle fatigue (HCF) and mechanical properties at elevated temperatures of 150, 200, 250 °C. It was found that the fatigue life was significantly improved by 8–10 times at the high stress amplitude of 140 MPa in the Zr-modified alloy at all different temperatures. The fatigue strength coefficient, σf', of the baseline alloy was 574.9, 589.8, and 514.8 MPa at 150, 200, and 250 °C, respectively, which was greatly increased to 1412.3, 620.1, and 821.6 MPa for the Zr-modified alloy. The tensile strength was considerably improved by 34%–50%, dependant on the testing temperatures. The improved fatigue and tensile properties in the Zr-modified alloy could be mainly ascribed to: (1) the refined microstructure, with α-Al grain size decreasing from 335 to 253 μm and the secondary dendrite arm spacing (SDAS) dropping from 39 to 28 μm; (2) the reduced porosity; and (3) the additional precipitates strengthening effect by the nano-sized Al–Si–Zr–Ti dispersoids.