Effect of Alloying Elements on the Sr Modification of Al-Si Cast Alloys

Federico Simone Gobber,Mario Rosso,Elisa Fracchia

doi:10.3390/met11020342

Federico Simone Gobber, Mario Rosso + Show 1 more

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https://doi.org/10.3390/met11020342

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Abstract

Strontium-based modifier alloys are commonly adopted to modify the eutectic silicon in aluminum-silicon casting alloys by changing the silicon shape from an acicular to a spherical form. Usually, the modifier alloy necessary to properly change the silicon shape depends on the silicon content, but the alloying elements’ content may have an influence. The AlSr10 master alloy’s modifying effect was studied on four Al-Si alloys through the characterization of microstructural and mechanical properties (micro-hardness and impact tests). The experimental results obtained on gravity cast samples highlighted the interdependence in the modification of silicon between the Si content and the alloying elements. After modification, a higher microstructural homogeneity characterized by a reduction of up to 22.8% in the size of intermetallics was observed, with a generalized reduction in secondary dendritic arm spacing. The presence of iron-based polygonal-shaped intermetallics negatively affects Sr modification; coarser silicon particles tend to grow close to α-Fe. The presence of casting defects such as bifilm reduces Sr modification’s beneficial effects, and little increase in absorbed impact energy is observed in this work.

Highlights

In recent years, aluminum-silicon casting alloys have been given high consideration thanks to their excellent mechanical properties and generally good corrosion resistance [1,2].these alloys are characterized by high fluidity, good weldability, and low thermal expansion coefficient [3].Several fields of application adopt aluminum alloys or aluminum composites [4], especially the automotive industry [5,6], where the light weight of aluminum alloys allows the reduction in cars’ weights and, greenhouse gas emissions [7]
Heat treatment usually involves a first step where solubilization takes place, as the alloying elements solubilize into the α-aluminum matrix, and a second step of artificial aging, where intermetallic phases nucleate into the α-aluminum matrix, increasing mechanical properties [13]
Three alloys belong to the hypoeutectic alloys group—EN AC 42100 (AlSi7Mg0.3), EN AC 45300 (AlSi5Cu1Mg), and EN AC 43500 (AlSi10MnMg)—while the fourth alloy belongs to the eutectic system, EN AC 48000 (AlSi12CuNiMg)

Summary

Introduction

Aluminum-silicon casting alloys have been given high consideration thanks to their excellent mechanical properties and generally good corrosion resistance [1,2].these alloys are characterized by high fluidity, good weldability, and low thermal expansion coefficient [3].Several fields of application adopt aluminum alloys or aluminum composites [4], especially the automotive industry [5,6], where the light weight of aluminum alloys allows the reduction in cars’ weights and, greenhouse gas emissions [7]. Aluminum-silicon casting alloys have been given high consideration thanks to their excellent mechanical properties and generally good corrosion resistance [1,2]. These alloys are characterized by high fluidity, good weldability, and low thermal expansion coefficient [3]. Heat treatment usually involves a first step where solubilization takes place, as the alloying elements solubilize into the α-aluminum matrix, and a second step of artificial aging, where intermetallic phases nucleate into the α-aluminum matrix, increasing mechanical properties [13]. Silicon shape modification takes place, and the eutectic silicon morphology changes from acicular to spherical; the magnitude of this transformation depends on the heat treatment parameters (times and temperatures) [14]

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