Interconnection of thermal parameters, microstructure, macrosegregation and microhardness of unidirectionally solidified Zn-rich Zn–Ag peritectic alloys

• Published in: Materials in engineering Vol. 63; pp. 848 - 855
• Main Authors: Dias, Marcelino, Brito, Crystopher, Bertelli, Felipe, Rocha, Otávio L., Garcia, Amauri
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.2014
• Subjects: Alloys; Castings; Constants; Macrosegregation; Microhardness; Microstructure; Peritectic alloys; Peritectic Zn–Ag alloys; Solidification; Zinc base alloys; Macrosegregation; Microstructure; Microhardness; Peritectic Zn–Ag alloys; Solidification
• ISSN: 0261-3069
• DOI: 10.1016/j.matdes.2014.07.002

•Transient growth of peritectic Zn–Ag alloys from the melt is experimentally examined.•The microstructure has dispersed dendritic primary crystals in a peritectic matrix.•Equations relating interphase spacing to growth thermal parameters are proposed.•Inverse solute macrosegregation profiles are observed for peritectic Zn–Ag alloys.•Microhardness depends on microstructural features only for single-phase Zn–Ag alloys. In this work, the microstructural evolution of Zn–3.2wt%Ag (hypoperitectic) and Zn–8wt%Ag (hyperperitectic) alloys during transient unidirectional solidification is investigated. The experimental results include solidification thermal parameters such as the growth rate (VL), thermal gradient (GL) and tip cooling rate (Ṫ), which are related to the microstructural interphase spacing (λ) by proposed experimental growth laws. It is shown that, the classical lamellar eutectic growth law λ2V=constant, applies to the growth of the peritectic Zn–Ag alloys examined, despite the different values of the constant associated with each alloy composition. In contrast, it is shown that identical functions of the form λ=constant (GL)−14 (VL)−1/8, and λ=constant (Ṫ-1/3) can be applied to both alloys examined. Positive solute macrosegregation was observed in regions close to the bottom of the castings. The dependence of microhardness (HV) on the length scale of the microstructures (including that of a single phase Zn 0.8wt%Ag alloy: λC− cellular spacing) is examined. An experimental Hall–Petch type power law is proposed relating the resulting microhardness to λC for the single phase alloy, and despite the segregation profiles and the alloying differences of the hypoperitectic and hyperperitectic alloys, the average microhardnesses of these alloys is shown to be essentially constant and similar along the castings lengths.