Dendritic Spacing and Macrosegregation Affecting Microhardness of an Al-Si-Mg Alloy Solidified Under Unsteady State Conditions

Cássio Da Silva,Danieli A P Reis,Thiago Soares,Amauri Garcia,Noé Cheung,Crystopher Brito

doi:10.1590/1980-5373-mr-2019-0390

Cássio Da Silva, Danieli A P Reis + Show 4 more

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https://doi.org/10.1590/1980-5373-mr-2019-0390

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Abstract

The prediction of microstructure morphology is fundamental for the manufacture of metallic components, since the expected levels of mechanical properties will be associated with the final aspects of the microstructure. In this work, an Al-7wt.%Si-3wt.%Mg alloy was directionally solidified in unsteady state conditions in order to investigate the influence of the addition of 3wt.%Mg to an Al-7wt.%Si alloy on the solidification evolution. The microstructure of the examined alloy is shown to be characterized by a more complex arrangement of phases, as compared to that of the Al-7wt.%Si alloy, which includes the binary (α-Al+Mg2Si) and refined ternary (α-Al+Si+Mg2Si+Fe-rich IMC) eutectic mixtures. A higher Vickers hardness profile is shown to be associated with a more refined microstructural arrangement. However, for cooling rates lower than 2K/s the microhardness is shown to increase with the increase in the microstructural spacing, which is shown to occur caused by Si macrosegregation and higher content of free Mg.

Highlights

Al-Si cast alloys have been widely employed in the manufacture of engine components, such as cylinder heads and engine blocks
The alloy was directionally solidified in a solidification apparatus, in which heat was removed from a water-cooled bottom, promoting vertical upward unsteady-state solidification
The following conclusions can be drawn from the present experimental study: A Si macrosegregation profile ranging from 6wt.% to 8.5wt.% at the bottom and top of the directionally solidified (DS) casting, respectively, was observed

Summary

Introduction

Al-Si cast alloys have been widely employed in the manufacture of engine components, such as cylinder heads and engine blocks This class of alloys combines high strength to weight ratio, excellent thermal conductivity, wear and corrosion resistance. All these characteristics and properties make these alloys potential materials to the replacement of cast iron[1,2]. One of the biggest challenges of the today’s designers is to render high efficiency with low energy consumption and low gas emission. This scenario has been ideal for the development of light alloys, and the development of aluminum alloys is far from being finished. This phase is very efficient to increase the mechanical strength at room temperature of 3xx.x and 6xxx series aluminum alloys 3-7

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