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Microstructure and Mechanical Properties of AZ91 Alloys by Addition of Yttrium

Research paper by Shou-Ren Wang, Pei-Quan Guo, Li-Ying Yang, Yanjun Wang

Indexed on: 13 Jun '08Published on: 13 Jun '08Published in: Journal of Materials Engineering and Performance



Abstract

Effects of yttrium (Y) on the microstructure and properties of as-cast Mg-Al-Zn (AZ91) alloys were studied. Y additions not only change the microstructure but also influence the mechanical properties of AZ91 alloy. AZ91 unmodified alloys under as-cast state indicate that eutectic phase Mg17Al12 is continuous and reticulated. Yttrium addition to AZ91 casting alloys has an important influence on the primary-phase and precipitation. When the Y content is 0.3 wt.%, no Y-containing compound was observed. When the Y content is 0.6 and 0.9 wt.%, Al2Y phase formed in the alloy and the growth morphology of eutectic Mg17Al12 phase is modified. When the Y content is further increased to 1.2 wt.%, the Al2Y phase becomes coarser and Mg17Al12 transforms into a cotton-shape structure. The results showed that Y can improve significantly as-cast microstructure of AZ91 alloys, refining Mg17Al12 phase and increasing in hardness and strength and decreasing in impact toughness and elongation.