Multi-Refinement Effect of Rare Earth Lanthanum on α-Al and Eutectic Si Phase in Hypoeutectic Al-7Si Alloy

Xiaoyan Wu,Haitao Jiang,Huarui Zhang,Hu Zhang,Zhenli Mi

doi:10.3390/met10050621

Xiaoyan Wu, Haitao Jiang + Show 3 more

Open Access

https://doi.org/10.3390/met10050621

Copy DOI

Abstract

The effect of La addition on primary α-Al and the eutectic Si phase of Al-7Si alloy is investigated systematically in this work. The results indicate that La addition causes a multi-refining efficiency on the microstructure of Al-7Si alloy, including refinement of α-Al grains and secondary dendrite arm spacing as well as eutectic Si particles. The grain size, secondary dendrite arm spacing and area of eutectic Si particles are decreased by 26.8%, 7.7% and 26.7%, respectively, with the addition of 0.1 wt.% La. It is also found that La-rich phases of Al2Si2La form and distribute in the vicinity of the eutectic Si phase. The crystal structure and lattice parameter of Al2Si2La phase are determined to be hexagonal (a = b = 0.405 nm, c = 6.944 nm) based on the TEM analysis results. The multi-refinement effects are mainly attributed to the increased constitutional undercooling caused by the low solubility of La in Al alloy and the growth-restricting factor caused by the Al2Si2La phase.

Highlights

Al-7Si alloys have been extensively used in die casting to produce components that comply with the mechanical performance of lightweight structures, environmental and other requirements
The mechanical properties of hypoeutectic Al-7Si cast alloy are controlled by the casting process, heat treatment process and physical metallurgy, such as chemical composition and microstructural features [1,2,3,4,5]
Considerable interest has been focused on the use of rare earth elements such as La, Ce, Sc, Yb, Er, Eu, etc., which have multiple effects including melt purification, grain refinement and eutectic

Summary

Introduction

The mechanical properties of hypoeutectic Al-7Si cast alloy are controlled by the casting process, heat treatment process and physical metallurgy, such as chemical composition and microstructural features [1,2,3,4,5]. Ductility, are accepted to be mainly controlled by microstructural features, normally the morphology and size of the α-Al primary phase, silicon particles and other precipitate phases which may be present in the microstructure [6]. Many efficient methods have been proposed to refine the primary α-Al phase and modify eutectic Si particles in order to improve the mechanical properties of the alloy. Micro-alloying additions such as refinement Ti, B [7,8]. Considerable interest has been focused on the use of rare earth elements such as La, Ce, Sc, Yb, Er, Eu, etc., which have multiple effects including melt purification, grain refinement and eutectic

Methods

Results

Conclusion