Strengthening Effect of Y 2 O 3 on AZ92 Magnesium Alloy Using Stir Casting Process
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Copyright Ó 2020 American Foundry Society https://doi.org/10.1007/s40962-020-00509-z
Abstract Strengthening effect of Y2O3 on AZ92 magnesium alloy using stir casting process has been investigated. Nominal amounts of Y2O3 (0, 1, 1.5, 2, 2.5 and 3 in wt%) were added into the melt vortex in the form of preformed master powder (Mg–30 wt% Y2O3) to improve their wettability with molten AZ92 alloy. The results showed clearly that without Y2O3 addition, the microstructure of the investigated alloy is composed of a-Mg which appeared as coarse dendritic structure, divorced eutectic-containing massive b-Mg17Al12 phase and super-saturated a-Mg solid solution. With Y2O3 addition, the distribution of Y2O3 particles was found within the inter-dendritic regions of the primary aMg phase. At 2.5 wt% Y2O3, a near uniform distribution of
Y2O3 particles along the grain boundaries of AZ92 alloy matrix was successfully obtained. However, further addition resulted in agglomeration of Y2O3 particles at 3 wt% addition level. The average tensile strength of the investigated AZ92 alloy was increased from 169 MPa to 198 MPa without a significant reduction in its ductility at optimum addition of 2.5 wt% Y2O3. The fracture mechanism has been also investigated.
Introduction
effectively improved with addition of 0.8 wt%Y-rich misch metal.7 Furthermore, cast AZ91 alloy with addition of 1.0 wt% Nd has considerably higher tensile properties.8 However, addition of these expensive RE elements to Mg alloys has possible problems due to oxidation at high temperature during material processing. In order to avoid these common problems, some papers used RE compounds instead of RE elements.12–14 It has been reported that the addition of submicron-sized yttria (30 vol%Y2O3) to cast Mg improves its tensile properties.12,13 It has been also published that adding nano-sized yttrium oxide (1.9 wt% Y2O3) as a reinforcement in magnesium via the disintegrated melt deposition (DMD) technique enhances the mechanical properties of the magnesium matrix.14 The stir casting route (also referred to as the vortex method) is a commercial, economical and most practical technique for the fabrication of particulate-reinforced metal-matrix Al
Magnesium alloys show potential applications as the lowest density among commercially available structural metallic materials for automotive and aerospace due to high specific strength, rigidity, energy saving and emission reduction.1–6 Magnesium cast alloys are dominant for about 85–90% of all products made of magnesium alloys. Several casting methods were introduced to produce components of Mg alloys, including sand casting, investment casting, permanent mold casting and high-pressure die casting.7 Meanwhile, improving the tensile strength of cast Mg alloys has become a critical issue to enable them to replace steel or Al components alloys in automobiles.6 The strength of cast Mg alloys can be improved by the addition of rare-earth (RE) elements (e.g., Y, Nd, Ce, La and Gd).8–11 The tensile yield strength of cast AZ91 alloy was
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