Effects of Si and Sr elements on solidification microstructure and thermal conductivity of Al\u2013Si-based alloys

Xun Zhang,Junchao Zhang,Wanqi Jie,Jiehua Li,Peter Schumacher,Yuli Zhou,Gu Zhong,Yunan Chen

doi:10.1007/s10853-022-07045-7

Abstract

Effects of Si and Sr on solidification microstructure and thermal conductivity of Al–Si binary alloys and Al–9Si–Sr ternary were investigated, respectively, with a special focus on the relationship between solidification microstructure and thermal conductivity. It was found that (i) in Al–Si binary alloys, with increasing Si content, α-Al grain size increases and then decreases when Si content is over 7 wt%, while the percentage of eutectic Si continuously increases, which significantly decreases the thermal conductivity and electrical conductivity, and (ii) in Al–9Si–Sr ternary alloys, the presence of Sr has no significant effect on α-Al grain, but effectively modifies eutectic Si and significantly improves the thermal and electrical conductivity. On this basis, two theoretical calculation models [the Maxwell model and the Hashin–Shtrikman (H–S) model] were used to elucidate the relationship between solidification microstructure and thermal conductivity. Compared with the Maxwell model, the H–S model fits better with the measured values. The obtained results are very helpful to the precise composition control during alloy design and recycling of Al–Si-based alloys with the aim to further improve the thermal conductivity of Al–Si-based alloys.Graphical abstract

Highlights

Of great necessity to further improve the thermal conductivity of Al–Si-based alloy, which can be directly related to the solidification microstructure
When the Si content is low, the Si in the melt does not react with these impurity elements to form intermetallic compounds
The increase of eutectic Si phase is responsible for the decrease in thermal conductivity and electrical conductivity of Al–Si binary alloys

Summary

Introduction

Hypoeutectic Al–Si-based alloys commonly contain 4–12 wt% Si and have been widely used due to their excellent casting properties, desirable mechanical properties and low costs [1]. Pure Al has an excellent thermal conductivity (237 Wm-1 K), the thermal conductivity of Al–Sibased alloy is generally low. The thermal conductivity of A380 alloy is only 96 Wm-1 K, less than half of pure Al, which is inadequate to meet the increasing application demands. It is, of great necessity to further improve the thermal conductivity of Al–Si-based alloy, which can be directly related to the solidification microstructure

Methods

Results

Discussion

Conclusion