Thermal Parameters and Microstructural Development in Directionally Solidified Zn-Rich Zn-Mg Alloys

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 2016-06, Vol.47 (6), p.3052-3064
• Main Authors: Vida, Talita A., Freitas, Emmanuelle S., Brito, Crystopher, Cheung, Noé, Arenas, Maria A., Conde, Ana, De Damborenea, Juan, Garcia, Amauri
• Format: Article
• Language: English
• Subjects: Alloy solidification; Alloys; Characterization and Evaluation of Materials; Chemistry and Materials Science; Cooling rate; Directional solidification; Magnesium base alloys; Materials Science; Metallic Materials; Metallurgy; Microstructure; Nanotechnology; Structural Materials; Surfaces and Interfaces; Thermal properties; Thermodynamics; Thin Films; Zinc; Zinc base alloys
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-016-3494-7

Transient directional solidification experiments have been carried out with Zn-Mg hypoeutectic alloys under an extensive range of cooling rates with a view to analyzing the evolution of microstructure. It is shown that the microstructure is formed by a Zn-rich matrix of different morphologies and competitive eutectic mixtures (Zn-Zn 11 Mg 2 and Zn-Zn 2 Mg). For 0.3 wt-pct Mg and 0.5 wt-pct Mg alloys, the Zn-rich matrix is shown to be characterized by high-cooling rates plate-like cells (cooling rates >9.5 and 24 K/s, respectively), followed by a granular–dendritic morphological transition for lower cooling rates. In contrast, a directionally solidified Zn1.2 wt-pct Mg alloy casting is shown to have the Zn-rich matrix formed only by dendritic equiaxed grains. Experimental growth laws are proposed relating the plate-like cellular interphase, the secondary dendritic arm spacing, and the eutectic interphase spacings to solidification thermal parameters, i.e ., cooling rate and growth rate. The experimental law for the growth of secondary dendritic spacings under unsteady-state solidifications is also shown to encompass results of hypoeutectic Zn-Mg alloys subjected to steady-state Bridgman growth.