The Effect of Solution Treatment on the Si Particles’ Morphology Evolution and the Thermal Conductivity and Tensile Properties of Sb-Modified Al-8Si-0.6Mg Alloys

Xiaopeng Liang,Li Wang,Xinming Guo,Yihao Wang,Huizhong Li,Liangjie Zhang

doi:10.3390/met12030377

Abstract

The effects of solution treatment time on the morphology evolution of Si particles and the thermal conductivity and tensile properties of Sb-modified alloys were studied. The results show that the evolution of Si particles follows four mechanisms: spheroidization, necking and splitting of particles with large aspect ratios, fusion of spherical particles, and coarsening controlled by diffusion. The first three mechanisms mainly occur at the early stage of solution treatment. The addition of Sb does not change the evolution law of the Si particles, but it does change the contribution of various evolution mechanisms, including promoting spheroidization, fusion, and coalescence, as well as significantly reducing the coarsening rate, which makes the thermal modification of Sb-modified alloys more effective. The increase in thermal conductivity during solution treatment is related to the decrease of the anharmonicity of lattice vibration, lattice wave scattering, and electron scattering of Si particles. The 0.4 wt. % Sb-modified alloy exhibits excellent tensile strength and elongation under as-cast T4- and T6-heat-treated conditions, because the modification significantly reduces the stress concentration of the Si particles and delays the germination and propagation of microcracks.

Highlights

Hypoeutectic Al-Si alloys are widely used in modern industrial fields due to their good casting properties, excellent wear resistance, and low density
Since the thermal conductivity and mechanical properties of hypoeutectic Al-Si alloys are mainly determined by the morphology of their Si particles [2,3], in recent years, researchers have used chemical modification, melt superheating treatment, semi-solid casting, and other techniques to modify the morphology of Si particles [4,5,6]
When the Sb content was 0.4 wt. % (Alloy-3), partial spherical Si particles appeared in alloys, while the rest were still needle-like

Summary

Introduction

Hypoeutectic Al-Si alloys are widely used in modern industrial fields due to their good casting properties, excellent wear resistance, and low density. Since the thermal conductivity and mechanical properties of hypoeutectic Al-Si alloys are mainly determined by the morphology of their Si particles [2,3], in recent years, researchers have used chemical modification, melt superheating treatment, semi-solid casting, and other techniques to modify the morphology of Si particles [4,5,6]. The coarsening controlled by particle coalescence and Ostwald ripening mechanisms is the main evolution law of Si particles. They did not discuss the evolution of Si particles at the early stage of solution treatment. The evolution law of Si particles and the contribution of various evolution mechanisms on the tensile properties and thermal conductivity were discussed, relative to the microstructure analysis of Si particles and the calculation of the scattering ability of the particle morphology of the electrons

Materials

Microstructure Characterization and Test Methods

Microstructure

Thermal Conductivity

Mechanical Properties

Mechanical properties