Heat Treatment-Induced Microstructure and Property Evolution of Mg/Al Intermetallic Compound Coatings Prepared by Al Electrodeposition on Mg Alloy from Molten Salt Electrolytes.

Tianyu Yao,Hezhou Liu,Kui Wang,Haiyan Jiang,Haiyan Yang,Qudong Wang,Wenjiang Ding,Jie Wei,Weiping Wu

doi:10.3390/ma14061407

Abstract

A method of forming an Mg/Al intermetallic compound coating enriched with Mg17Al12 and Mg2Al3 was developed by heat treatment of electrodeposition Al coatings on Mg alloy at 350 °C. The composition of the Mg/Al intermetallic compounds could be tuned by changing the thickness of the Zn immersion layer. The morphology and composition of the Mg/Al intermetallic compound coatings were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron backscattered diffraction (EBSD). Nanomechanical properties were investigated via nano-hardness (nHV) and the elastic modulus (EIT), and the corrosion behavior was studied through hydrogen evolution and potentiodynamic (PD) polarization. The compact and uniform Al coating was electrodeposited on the Zn-immersed AZ91D substrate. After heat treatment, Mg2Al3 and Mg17Al12 phases formed, and as the thickness of the Zn layer increased from 0.2 to 1.8 μm, the ratio of Mg2Al3 and Mg17Al12 varied from 1:1 to 4:1. The nano-hardness increased to 2.4 ± 0.5 GPa and further improved to 3.5 ± 0.1 GPa. The Mg/Al intermetallic compound coating exhibited excellent corrosion resistance and had a prominent effect on the protection of the Mg alloy matrix. The control over the ratio of intermetallic compounds by varying the thickness of the Zn immersion layer can be an effective approach to achieve the optimal comprehensive performance. As the Zn immersion time was 4 min, the obtained intermetallic compounds had relatively excellent comprehensive properties.

Highlights

Mg and its alloys have become increasingly promising candidates for structural materials in industrial applications in recent years, due to their low density and high specific strength
It can be seen that the surface and cross-sectional morphologies of the Zn layer varied significantly
After an 8-min Zn immersion, as shown in Figure 1d,h, the surface of the Mg alloy was completely covered by Zn, and a uniform and dense Zn layer with good flatness was obtained

Summary

Introduction

Mg and its alloys have become increasingly promising candidates for structural materials in industrial applications in recent years, due to their low density and high specific strength. Their poor surface properties, such as corrosion and wear resistance, cannot fulfill industrial demands, hindering wider application [1,2,3]. Inspired by the design of new alloys, surface modification has been regarded as a practical and effective approach to improve surface properties. Surface alloying of Mg alloys with Al has been attracting more and more attention since the formation of Mg/Al intermetallic compounds can improve corrosion and wear resistance. Many studies [11,12] have demonstrated that Mg/Al intermetallic compounds, especially

Methods

Results

Conclusion