Agradecimentos: The authors would like to thank the Brazilian research funding agencies FAPESP (Sa˜o Paulo Research Foundation – projects 2009/08478-1, 2013/09961-3, 2015/22143-3, 2021/11439-0 and 2022/05050-5), CNPq (National Council for Scientific and Technological Development—projects 470572/2011-6 and 140918/2018-3) and CAPES (Federal Agency for the Support and Improvement of Higher Education – notice 23/2016, ref. no. 88881.131045/2016-01) for providing financial support for this study. The authors are also indebted to the Faculty of Mechanical Engineering at the University of Campinas for the practical support very kindly provided Ver menos

Abstract: This work assesses the effect of cooling rate (T\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{T}$$\end{document}) on the solidification kinetics and microstructural evolution of a 319 aluminum alloy with and without the addition of Al-5 wt%Ti-1wt%B grain refiner. Directionally solidified samples were produced under various cooling rates (from 0.05 to 40 degrees C/s). Microstructure coarsening was then quantitatively analyzed by measuring grain size (GS) and primary (lambda 1), secondary (lambda 2) and average (lambda L) dendrite arm spacing. The results show that polarized optical images can be used to identify dendrite fragments between neighboring primary dendrites, allowing a more accurate microstructural analysis after the addition of grain refiner. The results also show that, for a given T\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{T}$$\end{document}, although GS is reduced after the addition of grain refiner, the respective values of lambda 1, lambda 2 and lambda L remain practically the same. In other words, the grain refiner only affects nucleation and not grain growth. Experimental growth equations are proposed to represent this behavior. Furthermore, lambda L is shown to be a good parameter for evaluating microstructural refinement Ver menos