Role of Heat Treatment on the Tensile Properties and Fractography of Al–1.2Si–2.4Cu and Al–8.0Si–2.4Cu Cast Alloys Modified with Ce, La and Sr Addition

Abstract

The present research study aims at studying the influence of the additions of Ce and La elements (0.2–1.0%) on room temperature tensile properties of Al–1.2Si–2.4Cu and Al–8.0Si–2.4Cu-alloys, with relatively low and high Si, respectively. The results showed that T6-treated alloys, Sr-modified alloys or those containing Ce/La exhibited UTS values comparable to the solution heat-treated, T5 and T7-treated alloys. The influence of 0.2 wt% RE (Ce/La) on tensile properties is similar to that caused by adding 150 ppm Sr. The strengthening behavior of addition of 0.2%RE is attributed to the size and distribution of RE intermetallics coupled with their low volume fraction. Under these conditions, the alloys act as composite materials. Stabilization at 250 °C for 200 h produces a marked decrease in the alloy strength, with an increase in ductility values. Additions of 0.2 wt% Ce or La marginally improved the strength of the B0 and D0 alloys (10–15 MPa) following 1 h of stabilization at 250 °C. The fracture surfaces were examined using scanning electron microscopy, whereas the longitudinal sections beneath the fractures surfaces were examined using optical microscopy.