Effect of Vanadium Micro-alloying on the Microstructure and Mechanical Properties of Stir Cast Al 354.0 Alloy

The present work investigates the effect of vanadium (V) micro-alloying addition on the microstructural evolution and mechanical properties of Al 354.0 alloy in as-cast and T6 condition. In particular, Al 354.0 with and without 0.3 wt.% V was developed by squeeze casting technique. The as-cast ingots were subjected to two types of heat treatment schedules, i.e., solution heat treatment at 495 °C for 8 h, followed by rapid water quenching and artificial aging at 190 °C for 2 h (T6), and solution heat treatment at 515 °C for 10 h, followed by rapid water quenching and artificial aging at 210 °C for 6 h (MT6), to modify the microstructure, morphology, and distribution of Al-, Cu-, and Mg-containing secondary phase(s). The phase and microstructure of unmodified and 0.3 wt.% V-modified alloys were analyzed using x-ray diffraction, optical microscopy, and field emission scanning electron microscopy coupled with energy-dispersive x-ray spectroscopy. Detailed analyses show that AlCu/AlCu(SiMg), AlSiMg, and AlSi were the strengthening phases in the unmodified alloy, whereas 0.3 wt.% V-modified alloy contains AlV/AlV(Mg), AlCu, MgSi, AlSi, and Al(SiCuMg) as the primary strengthening phase(s). A subtle increase in the mechanical properties was evident in the 0.3 wt.% V-modified alloy compared to unmodified alloy at ambient temperature due to the presence of AlV/AlV(Mg) fine precipitates and Al(SiCuMg) intermetallic along the grain boundaries (GBs) preventing dislocation movement. T6 treatment resulted in a grain growth where needle/plate morphology of eutectic silicon was partially converted into spheroidal morphology, and AlCu/AlSiCuMg, MgSi, and AlV/AlV(Mg) intermetallic phases emerged increasing the tensile (0.3% V modified vs. unmodified; YS: ~ 287 vs. ~ 268 MPa, UTS: ~ 330 vs. ~ 334 MPa, elongation: ~ 1.5% vs. ~ 2.6%), compression (0.3% V modified vs. unmodified YS: ~ 497 vs. ~ 460 MPa, UCS: ~ 790 vs. ~ 776 MPa, compressive strain: ~ 40% vs. ~ 42%), and wear properties. However, modified T6 treatment (MT6) resulted in a grain growth where needle/plate morphology of eutectic silicon converted into spheroidal morphology, and AlCu partially and MgSi precipitates along the GBs were completely dissolved in the α-Al matrix by incipient melting improving the ductility (~5.9%) at the expense of yield strength (~104 MPa) and ultimate tensile strength (~218 MPa).