Interconnection of thermal parameters, microstructure, macrosegregation and microhardness of unidirectionally solidified Zn-rich Zn–Ag peritectic alloys Marcelino Dias a , Crystopher Brito a , Felipe Bertelli a , Otávio L. Rocha b , Amauri Garcia a,⇑ a Department of Manufacturing and Materials Engineering, University of Campinas, UNICAMP, 13083-970 Campinas, SP, Brazil b Federal Institute of Education, Science and Technology of Pará, IFPA, Almirante Barroso Avenue 1155, 66093-020 Belém, PA, Brazil article info Article history: Received 17 May 2014 Accepted 2 July 2014 Available online 14 July 2014 Keywords: Solidification Microstructure Peritectic Zn–Ag alloys Macrosegregation Microhardness abstract In this work, the microstructural evolution of Zn–3.2 wt%Ag (hypoperitectic) and Zn–8 wt%Ag (hyperperitectic) alloys during transient unidirectional solidification is investigated. The experimental results include solidification thermal parameters such as the growth rate (V L ), thermal gradient (G L ) and tip cooling rate ( _ T ), which are related to the microstructural interphase spacing (k) by proposed experimental growth laws. It is shown that, the classical lamellar eutectic growth law k 2 V = 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 k = constant (G L ) 14 (V L ) 1/8 , and k = constant ( _ T 1=3 ) can be applied to both alloys examined. Positive sol- ute 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 0.8 wt%Ag alloy: k C cellular spacing) is examined. An experimental Hall–Petch type power law is proposed relating the resulting microhardness to k C for the single phase alloy, and despite the segregation profiles and the alloying differences of the hypoperitectic and hyperperitectic alloys, the average micro- hardnesses of these alloys is shown to be essentially constant and similar along the castings lengths. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Peritectic and eutectic reactions can be found in metallic, organic and inorganic materials. The peritectic invariant transformation occurs on cooling of a liquid phase (L) with a primary solid phase (a) to form a second solid phase (b) below the peritectic tempera- ture. A competitive growth occurs with the dissolution of the pri- mary phase, to permit the second phase to freeze out from the liquid, i.e. the peritectic reaction will occur where these three phases are in contact (an equilibrium situation that is generally not observed in practice). In another growth mechanism, called the peri- tectic transformation, once the a phase is enveloped by b, additional transformation is controlled by diffusion through the b phase [1–3]. However, a variety of microstructures can be obtained from during solidification of peritectic alloys under non-equilibrium conditions, which depend mainly on the thermal parameters during solidifica- tion (thermal gradient, G L , growth rate, V L , and cooling rate, _ T ) and the nucleation conditions. Possible microstructures include: cellular [4], bands [5,6], lamellar [7], eutectic type structures [8], and den- dritic structures [9]. Zinc-based alloys are used in the manufacture of a number of components of the electrical/electronics industry, e.g. connectors, mobile-phone antennae, transformer cores, heat sinks, shutter mechanisms in cameras, applications requiring electromagnetic shielding, etc. [10]. Despite the importance of Zn-based alloys, studies focusing on correlations between solidification thermal parameters, microstructures of peritectic Zn–Cu and Zn–Ag alloys, and application properties are sparse. Ma et al. [11,12], carried out studies on steady-state growth of Zn-rich Zn–Cu alloys for a range of compositions between 1.53 and 7.37 wt%Cu. They reported the occurrence of two-phase regular and plate-like cellular microstruc- tures in a range of compositions near the peritectic point. Brito et al. [4,13], carried out transient solidification experiments on Zn–1.0 wt%Cu (single-phase) and Zn–2.2 wt%Cu (hypoperitectic) alloys, in which experimental growth laws relating the length scale of the cellular microstructure to solidification thermal parameters are proposed [4] and microstructural features and macrosegrega- tion are related to the alloys microhardnesses [13]. The electro- chemical corrosion behavior of a peritectic Zn–Cu alloys as a http://dx.doi.org/10.1016/j.matdes.2014.07.002 0261-3069/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +55 19 3521 3320; fax: +55 19 3289 3722. E-mail address: amaurig@fem.unicamp.br (A. Garcia). Materials and Design 63 (2014) 848–855 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes