Influences of Cu Content on the Microstructure and Strengthening Mechanisms of Al-Mg-Si-xCu Alloys

Yuqiang Chen,Hao Zhang,Qiang Hu,Biwu Zhu,Huiqun Liu,Wenhui Liu,Xiao Liu,Suping Pan

doi:10.3390/met9050524

Yuqiang Chen, Hao Zhang + Show 6 more

Open Access

https://doi.org/10.3390/met9050524

Copy DOI

Abstract

The effects of the Cu content on the microstructure and strengthening mechanisms of the Al-Mg-Si-xCu alloys were systematically investigated using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), transmission electron microscopy (TEM), and mechanical tensile tests. The results show that, the strengthening mechanisms change with the Cu content. For as-quenched alloys, solution strengthening (σSS) is predominant when the Cu content ≥2.5 wt.%, and of equivalent importance as grain size strengthening (σH-P) when the Cu content ≤1.0 wt.%. With respect to peak-aged alloys, precipitation strengthening (σppt) is predominant when the Cu content ≥2.5 wt.%, but σSS becomes predominant when the Cu content is 4.5 wt.%. As the Cu content increases from 0.5 to 4.5 wt.%, the main type of precipitates in alloy tends to change from a β″ phase to Q′ phase, and then to a θ′ phase. Among the three types of precipitates, θ′-precipitate causes the largest increase in yield strength (σ0.2) and the largest decrease rate in elongation. β″-precipitate leads to the smallest increase in σ0.2 and the smallest decrease rate in elongation. The increase of Cu content reduces Si solubility in the Al matrix and thus decreases the nucleation rate of β″ phase during subsequent aging.

Highlights

Al-Mg-Si-xCu alloys have been widely used in the fields of aviation, rail transportation, and the automobile industry, due to the combination of good formability and excellent corrosion resistance [1,2]; the relatively low strength has restricted their applications, due to the increasing requirements for larger, faster vehicles
The average grain size (AGZ) and grain aspect ratio (GAR) of these alloys were were calculated, and the results are listed in Table
A systematic study was performed on the evolution of the microstructural features and strengthening mechanisms of Al-Mg-Si-xCu alloys with different Cu contents, and the following conclusions were drawn: (1) The Cu content exerts a grain refinement effect on both as-extruded and as-quenched

Summary

Introduction

Al-Mg-Si-xCu alloys have been widely used in the fields of aviation, rail transportation, and the automobile industry, due to the combination of good formability and excellent corrosion resistance [1,2]; the relatively low strength has restricted their applications, due to the increasing requirements for larger, faster vehicles. It is necessary to develop Al-Mg-Si-xCu alloys with better mechanical properties [3,4]. Show that the strength of such an alloy can be enhanced by Cu additions as low as 0.1 wt.%. Zheng et al [9] discovered that, when the addition of Cu increased to 4.0 wt.%, the strength of the alloy was increased by more than 37.5%. On account of the increasing demand for high-strength alloys, the recent

Methods

Results

Discussion

Conclusion