Relationship between Microstructure Evolution and Tensile Properties of AlSi10Mg Alloys with Varying Mg Content and Solidification Cooling Rates

Maressa Gandolfi,José Eduardo Spinelli,Leonardo Fernandes Gomes,Rodrigo André Valenzuela Reyes,Amauri Garcia,Marcella Gautê Cavalcante Xavier

doi:10.3390/met11071019

Maressa Gandolfi, José Eduardo Spinelli + Show 4 more

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https://doi.org/10.3390/met11071019

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Abstract

This work explored and contrasted the effect of microstructure on the tensile properties of AlSi10Mg alloys generated by transient directional solidification depending on variations in cooling rate and magnesium (Mg) content (i.e., 0.45 and 1 wt.% Mg), with a focus on understanding the dendritic growth and phases constitution. Optical and scanning electron (SEM) microscopies, CALPHAD, and thermal analysis were used to describe the microstructure, forming phases, and resulting tensile properties. The findings showed that the experimental evolution of the primary dendritic spacing is very similar when both directionally solidified (DS) Al-10 wt.% Si-0.45 wt.% Mg and Al-10 wt.% Si-1 wt.% Mg alloys samples are compared. The secondary dendritic spacing was lower for the alloy with more Mg, especially considering the range of high growth velocities. Moreover, a greater fraction of (Al + Si + Mg2Si) ternary eutectic islands surrounding the α-Al dendritic matrix was noted for the alloy with 1 wt.% Mg. As a result of primary dendritic spacings greater than 180 μm related to lower cooling rates, slightly higher tensile properties were attained for the Al-10 wt.% Si-0.45 wt.% Mg alloy. In contrast, combining dendritic refining (<150 μm) and a larger Mg2Si fraction, fast-solidified DS Al-10 wt.% Si-1 wt.% Mg samples exhibited higher tensile strength and elongation. The control of cooling rate and fineness of the dendritic array provided a new insight related to the addition of Mg in slightly higher levels than conventional ones, capable of achieving a better balance of tensile properties in AlSi10Mg alloys.

Highlights

Introduction published maps and institutional affilEven though the AlSi10Mg (Al-10 wt.% Si-Mg) alloys may be processed through a variety of techniques (i.e., additive manufacturing (AM), high pressure die casting (HPD), and permanent mold casting (PM), among others), a better understanding of the solidification cooling rate effects on the microstructure and mechanical properties remains a task to be achieved
85% of the length of the castings from the cooled bottom. The microstructure of both alloys is formed by an α-Al matrix with a dendritic arrangement and well-defined primary (λ1)
While the properties of the Al-10 wt.% Si-0.45 wt.% Mg alloy are superior for coarser λ1 spacing, the properties of Al-10 wt.% Si-1 wt.% Mg alloy are superior and stand out in relation to the entire data set for more refined microstructure arrangements

Summary

Introduction

Even though the AlSi10Mg (Al-10 wt.% Si-Mg) alloys may be processed through a variety of techniques (i.e., additive manufacturing (AM), high pressure die casting (HPD), and permanent mold casting (PM), among others), a better understanding of the solidification cooling rate effects on the microstructure and mechanical properties remains a task to be achieved. In addition to more precise control of solidification process variables and resulting microstructures, a challenge that arises is the increase in the Mg content of these alloys (usually not higher than 0.5 wt.%) to reduce or even eliminate heat treatment steps, which would be an appreciable gain in the processing routes. The main studies and their findings will be reported demonstrating processing and microstructure aspects regarding the as-cast AlSi10Mg alloys. PM casting processes—unlike HPD, which is carried out by injecting the molten metal into a mold at high speed, high cooling rates (101 –102 ◦ C/s), and high pressure—are iations.

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