Effect of Heat Treatment on Microstructural Evolution and Microhardness Change of Al-5Zn-0.03In-1Er Alloy

Jin Cui,Zhengbing Xu,Jiajin Hu,Jianmin Zeng,Zhichao Tang,Xiaoyang Chen,Muzhi Yu

doi:10.3390/met12030370

Abstract

Adding an appropriate amount of Er element to Al-Zn-In alloys can improve the electrochemical performance of Al alloys; it is convenient to study the electrochemical behavior of the alloy in the rest of our work. However, Er segregation in solid solutions which reduced the comprehensive properties of alloys was difficult to reduce and there was no report on the homogenization of Al-Zn-In alloys. We found that the ultra-high temperature treatment (UHTT) can obviously reduce Er segregation. To explore the better homogenization treatment and the microstructure evolution of Al-5Zn-0.03In-1Er alloy after UHTT, we carried out a series of heat treatments on the alloy and characterized the microstructure of the alloy by optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy spectrum analysis (EDS) and transmission electron microscopy (TEM). The results showed that the main element Er of the Al-Zn-In-Er was largely enriched in grain boundaries after UHTT; the distribution Zn and In was almost unchanged. The as-cast Al-Zn-In-Er alloy consisted mainly of α(Al) solid solution and Al3Er phase. As the temperature of UHTT increased and the treatment time prolonged, the precipitated phase dissolved into the matrix, and there were dispersed Al3Er particles in the crystal. The proper UHTT for reducing the interdendritic segregation of the alloy was 615 °C × 32 h, which was properly consistent with the results of the evolution of the statistical amount of interdendritic phase, the line scanning analysis and the microhardness. Moreover, the microhardness of the alloy after treatment of 615 °C × 32 h was obviously higher than that of the as-cast alloy because of the anchoring effect of Al3Er nanoparticles on the movement of dislocations.

Highlights

The rapid development of high-tech devices such as aviation and aerospace devices is increasingly demanding on the performance of Al-based alloys
Different microstructures are exhibited under different treatment, which is extremely significant to control the microstructure evolution during heat treatment in order to obtain excellent mechanical properties
Some circular samples were cut from the cast experimental alloy for optical microscopy (OM), X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests

Summary

Introduction

The rapid development of high-tech devices such as aviation and aerospace devices is increasingly demanding on the performance of Al-based alloys. Adding a small amount of rare earth elements can improve the electrochemical performance of the alloys [1,2]. Studies have shown that adding an appropriate amount of Er to the Al alloy can form an Al3 Er phase with the stable L12 structure [3,4]. According to the Al-Er binary phase diagram [3], there is eutectic Al-Al3 Er on the left side of the phase diagram, and the eutectic point composition is about 6 wt.% Er. Generally speaking, the content of Er in the experimental alloy is much less than 6 wt.%. S. et al, [5]

Methods

Results

Discussion

Conclusion