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

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 degrees 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, sigma(f)', of the baseline alloy was 574.9, 589.8, and 514.8 MPa at 150, 200, and 250 degrees 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 alpha-Al grain size decreasing from 335 to 253 mm and the secondary dendrite arm spacing (SDAS) dropping from 39 to 28 mm; (2) the reduced porosity; and (3) the additional precipitates strengthening effect by the nano-sized Al-Si-Zr-Ti dispersoids. (C) 2019 Elsevier B.V. All rights reserved.