Effects of Alloying Elements and Testing Temperature on the Q-Index of Al–Si Based Alloys

Abstract

The present study was performed on the 354 (Al–9wt%Si–1.8wt%Cu–0.5wt%Mg)-based alloy to which measured amounts of Zr, Ni, Mn and Sc were added. Tensile test bars were prepared from the different 354 alloys using an ASTM B-108 permanent mold. The test bars were solution heat-treated using a one-step or a multi-step solution heat treatment, followed by quenching in warm water, and then artificial aging employing different aging treatments. Tensile bars were thereafter tested at 25 and 250 °C. Analysis of the tensile data was carried out using quality charts and color contour maps. The results show that at room temperature, Alloy R (354 + 0.25%Zr) showed the best quality index values after T6 treatment, i.e., 411 and 418.64 MPa without, and with 200-h stabilization at 250 °C, respectively. Alloy U (354 + 0.25%Zr + 0.75%Mn) displayed a Q-value of 397.84 MPa after T6 treatment (with no stabilization) and 404.62 MPa following T6 treatment and 200-h stabilization at 250 °C before testing. At 250 °C testing temperature and after 200-h stabilization at 250 °C, the strength of all alloys exhibited a decrease in strength with an increase in ductility being related to the softening, which occurred due to the onset of overaging.