Effect of transition metals on energy absorption during strain-controlled fatigue of an aluminum alloy

Tensile and low cyclic fatigue tests were used to assess the influence of micro-additions of Ti/V/Zr on the performance of Al–7Si–1Cu–0.5Mg (wt.%) alloys in the as-cast and T6 heat-treated conditions and their improvement was compared to the base alloy. The microstructure of the as-cast Al–7Si–1Cu–0.5Mg (wt.%) base and modified alloys consisted of α-Al, eutectic Si, and Cu, the Mg- and Fe-based phases Al 2.1 Cu, Al 8.5 Si 2.4 Cu, Al 7.2 Si 8.3 Cu 2 Mg 6.9 and Al 14 Si 7.1 FeMg 3.3 . In addition, the micro-sized Ti/V/Zr-rich phases Al 6.8 Si 1.4 Ti, Al 21.4 Si 4.1 Ti 3.5 VZr 3.9 , Al 6.7 Si 1.2 TiZr 1.8 , Al 2.8 Si 3.8 V 1.6 Zr and Al 5.1 Si 35.4 Ti 1.6 Zr 5.7 Fe were identified in the modified alloys. It was also noticed that increasing the content of Ti–V–Zr changed the morphology of Ti/V/Zr-rich phase. The tensile test results showed that the T6 heat-treated alloy modified with the addition of a higher content of Ti–V–Zr achieved the highest tensile strength of 343 MPa over the base alloy and alloys modified with additions of Ti, Ti–Zr and lower contents of Ti–V–Zr. The plastic strain energy density coefficient of the alloy modified with the addition of a higher content of Ti–V–Zr in the T6 temper condition was higher than the other studied alloys and reached 162 MJ m −3 . The fatigue life of the same alloy was considerably longer than that of the other studied alloys, including the base alloy. The fractography revealed that all the studied alloys showed similar fracture behavior. The tensile cracks propagated through the eutectic Si and primary phases, exhibiting intergranular fracture along with some cleavage-like features of the plate-shaped Zr–Ti–V-rich intermetallics with the presence of fatigue striations on the latter, indicating their ductile nature. It is believed that the morphological changes of intermetallic precipitates containing Zr, Ti and V enhance the fatigue life of the alloy modified with additions of larger amounts of Ti–V–Zr in the T6 condition.