Microstructure Characteristics of As-Cast Zn-16Al Alloy during Homogenization Treatment

Homogenization treatment of as-cast Zn-16Al alloy was investigated. Effects of various parameters on the microstructure transformation and the mechanical properties were researched with the methods of hardness test, tensile test, scanning electron microscopy analysis, etc. The results indicate that 360°C × 8 h with furnace cooling is the most reasonable homogenization process for Zn-16Al alloy. Additionally, a new kind of needle-shaped or shuttle-shaped η phase is observed during the furnace-cooled homogenization, which exhibits an extremely regular distribution with an included angle of 120° and a location between the lamellar eutectoids (α + η). The formation of the new η phase is mainly attributed to the Al-depleted-zones left behind by the decomposition of supersaturated α phase. The α′ phase precipitating from eutectoid reaction α → α′ + η contains a much higher Al-content than that of original α phase.

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