High damping capacity of Al-40Zn alloys with fine grain and eutectoid structures via Yb alloying

Undesirable damping capacity and mechanical properties resulted from coarse α-Al dendrites and network eutectoid structures of high-Zn aluminum casting alloys are the main problem restricting their practical applications. Rare-earth microalloying offers an effective means to improve the microstructure of Al alloys. Hence, in this study, the microstructure, damping capacities, and mechanical properties of newly developed Al–40Zn–xYb (x = 0, 0.1, 0.3, 0.5 wt%) cast alloys were systematically evaluated by optical microscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The experimental results indicated that Yb3Zn11 and YbZn2 intermetallic compounds were successively formed by adding Yb in Al–40Zn alloys. The α-Al grain and the α + η eutectoid structures of the Al–40Zn alloy were significantly refined with increasing Yb content. Among them, the 0.3Yb alloy exhibited the smallest grain size (approximately 157 µm) and the minimum interlamellar spacing of the α + η eutectoid structures (approximately 243 nm). Moreover, the same alloy presented partial curved α + η eutectoid structures. The 0.3Yb alloy possessed optimal damping capacity and mechanical properties; in comparison with Al–40Zn, the damping values of 0.3Yb increased by 74.7% at 300 K and by 32% at the internal friction peak P (approximately 563 K), whereas the yield strength, tensile strength, and elongation increased by 25.4%, 14.9%, and 58.6%, respectively. The remarkable improvement in damping capacity and mechanical properties was mainly attributed to the high density of grain boundaries (GBs) and fine α + η structures.