Influence of upward and horizontal growth direction on microstructure and microhardness of an unsteady-state directionally solidified Al-Cu-Si alloy

Raimundo Lucivaldo Marães De Araújo,Daniel Joaquim Da Conceição Moutinho,Otávio Fernandes Lima Da Rocha,Rafael Hideo Lopes Kikuchi,Laércio Gouvea Gomes,André Santos Barros,Fernando De Almeida Gonçalves,Antonio Luciano Seabra Moreira

doi:10.1590/s1517-707620160001.0024

Abstract

In order to analyze the effect of the growth direction on dendrite arm spacing (λ1) and microhardness (HV) during horizontal directional solidification (HDS), experiments were carried out with the Al-3wt.%Cu-5.5wt.%Si alloy and the results compared with others from the literature elaborated for upward directional solidification (UDS). For this purpose, a water-cooled directional solidification experimental device was developed, and the alloy investigated was solidified under unsteady-state heat flow conditions. Thermal parameters such as growth rate (VL) and cooling rate (TR) were determined experimentally and correlations among VL, TR, λ1 and HV has been performed. It is observed that experimental power laws characterize λ1 with a function of VL and TRgiven by: λ1=constant(VL)-1.1 and λ1=constant(TR)-0.55. The horizontal solidification direction has not affected the power growth law of λ1 found for the upward solidification. However, higher values of λ1 have been observed when the solidification is developed in the horizontal direction. The interrelation of HV as function of VL, TR and λ1 has been represented by power and Hall-Petch laws. A comparison with the Al-3wt.%Cu alloy from literature was also performed and the results show the Si element affecting significativaly the HV values.

Highlights

Aluminum alloys castings have a fundamental role in the metal-mechanics industry
In order to analyze the effect of the growth direction on dendrite arm spacing ( 1) and microhardness (HV) during horizontal directional solidification (HDS), experiments were carried out with the Al-3wt.%Cu5.5wt.%Si alloy and the results compared with others from the literature elaborated for upward directional solidification (UDS)
A comparison with the Al-3wt.%Cu alloy from literature was performed and the results show the Si element affecting significativaly the HV values

Summary

Introduction

Aluminum alloys castings have a fundamental role in the metal-mechanics industry. Nowadays these alloys are supplied in a wide range of chemical compositions [1-12]. The morphology of as-cast microstructures, characterized mainly by cellular and dendritic patterns, and their scales represented by primary, secondary and tertiary arm spacings ( 1, 2 and 3, respectively) control the segregation profiles and the formation of secondary phases within intercellular and interdendritic regions, which determine the final properties of castings [1,2]. This is known that the values of 1, 2 and 3 are strongly influenced by solidification thermal parameters such as growth rate (VL) and cooling rate (TR) [1,2,3,7-12]. Several directional solidification studies have been reported in the literature to characterize and quantify these parameters as a function of solute concentration C0, VL and TR

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