On the Natural Convection in the Columnar to Equiaxed Transition in Directionally Solidified Aluminum-based Binary and Multicomponent Alloys

Carlos Henrique Ursolino Gomes,Antonio Luciano Seabra Moreira,Rafael Hideo Lopes Kikuchi,Maria Adrina Paixão de Sousa da Silva,Otávio Fernandes Lima da Rocha,André dos Santos Barros,José Nazareno Santos da Silva

doi:10.1590/1516-1439.036315

Abstract

In order to investigate the effect of natural convection in columnar to equiaxed transition (CET), Al-3.0wt.%Cu and Al-3.0wt.%Cu-5.5wt.%Si alloys ingots were obtained during the transient horizontal directional solidification (THDS). Aiming to analyze the effect of superheat in the formation of the macrostructure in ternary Al-Cu-Si alloy, the experiments were conducted with three superheat temperatures above the liquidus temperature of the ternary alloy. A water-cooled solidification experimental device was used. Continuous temperature measurements were made during solidification at different positions in the casting and the data were automatically acquired. Thermal analysis has been applied to determine the thermal parameters such as growth rate (VL), cooling rate (TR) and temperature gradient (GL), whose values have been interrelated with the CET. The observation of the macrostructures has indicated that the resulting thermosolutal convection combined with superheat seem to favor the transition, which did not occur in a single plane, for all ingots obtained, i.e., it has been seen in a range of positions in ingots. The addition of Si element in binary Al-Cu alloy anticipates the CET. A comparison with experimental results for CET occurrence in different growth directions has been carried out.

Highlights

Aluminum casting alloys have properties which are of great industrial interest, such as low density, good corrosion resistance, high thermal and electrical conductivities, good combination of mechanical properties, good workability in machining processes and mechanical forming
It is known from the literature that the columnar to equiaxed transition (CET) is dependent of VL, GL and TR and that during transient solidification these thermal parameters vary with time and position
In order to investigate the effect of these parameters on the CET occurrence in analyzed alloys, cooling curves from the Figure 4 were used to determine the displacement of the liquidus isotherm as well as VL, TR, and GL values

Summary

Introduction

Aluminum casting alloys have properties which are of great industrial interest, such as low density, good corrosion resistance, high thermal and electrical conductivities, good combination of mechanical properties, good workability in machining processes and mechanical forming. These alloys are produced in various systems and solute contents[1]. The literature presents a number of theoretical and experimental, focusing on the macrostructural and microstructural evolution of binary aluminum alloys, there are few studies in the literature addressing important families of multicomponent aluminum alloys In this context, the Al-Cu-Si ternary is a system of particular outstanding properties such as high mechanical strength, low weight and very good fluidity. The potential of such alloys has attracted the attention of researchers with a view to investigating the microstructure evolution, and the formation of both macrosegregation and porosity during the solidification process

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Results

Conclusion