Abstract
The principal aim of the present research work was to compare the role of dispersoids Al2O3 (∼15 μm average particle size) and SiC (∼15 μm average particle size) with that offered by Zr- and Ni-based intermetallics (∼35–70 μm average particle size) on the hardening of cast aluminum 354 alloy (9.1% Si, 0.12% Fe, 1.8% Cu, 0.008% Mn, 0.6% Mg, and 87.6% Al) at ambient temperature. There is no observable poisoning effect on the refinement of grain size after the addition of Zr to the alloys investigated in this study. The tensile test results were examined in light of the microstructural features of the corresponding alloy samples. The contribution of the added dispersoids or Ni and Zr alloying elements on the tensile properties of the 354 alloys was determined employing ∆P plots (where P = Property, UTS, YS, or %El), using the base alloy (in the as-cast condition) as a reference point. The tensile results were supported by investigating the precipitation-hardening phases using scanning and transmission electron microscopy as well as examining the fracture surfaces of selected conditions applying field emission scanning electron microscopy. The results show that, in all cases, Al2Cu phase is the main hardening agent. The contribution of about 1.5 vol% of SiC or Al2O3 to the strength of the base alloy is higher than that offered by Zr- and Ni-based intermetallics, under the same aging treatment.
Highlights
Dispersoids are defined as small and numerous finely divided particles of one substance dispersed in another
Fracture of these particles under loading can lead to the nucleation of cracks ahead of the main advancing crack. e effect of Cr and Mn addition and heat treatment on AlSi3Mg casting alloy was investigated by Tocci et al [3] who found that Cr- and Mn-based dispersoid particles improve Vickers microhardness of the aluminum matrix compared to the base alloy after solution treatment and quenching, which is in accordance with the dispersion-hardening mechanism
After adding Sr, no mobility of the residual liquid is observed even at the high level of 45%. is explanation, in addition to the change in the dendrite shape presented in Figure 2(b), contradicts the model presented by Argo and Gruzleski [31] which suggests that, in unmodified alloys, the eutectic is characterized by its irregular solid/ liquid interface, leading to entrapping of small pockets of liquid between advancing solidification fronts, causing the formation of microporosity
Summary
Dispersoids are defined as small and numerous finely divided particles of one substance dispersed in another. Eir size is in the range of 0.1 to 1.0 μm, which is made use of to reduce the alloy grain size Fracture of these particles under loading can lead to the nucleation of cracks ahead of the main advancing crack. E effect of Cr and Mn addition and heat treatment on AlSi3Mg casting alloy was investigated by Tocci et al [3] who found that Cr- and Mn-based dispersoid particles improve Vickers microhardness of the aluminum matrix compared to the base alloy after solution treatment and quenching, which is in accordance with the dispersion-hardening mechanism. Eir main conclusion was that the incorporation of Si in the metastable Al3Zr type of dispersoid particles could increase the nucleation rate by reducing the volume-free energy of formation of the dispersoid particles. Kenyon et al [8] added that changing the dispersoid volume fraction, size, and morphology has important implications for the pinning effectiveness of the dispersoids
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