Effects of the Mg/Si Ratio on Microstructure, Mechanical Properties, and Precipitation Behavior of Al⁻Mg⁻Si⁻1.0 wt %-Zn Alloys.

Yong Li,Guangming Xu,Jiadong Li,Guanjun Gao,Hongshuang Di,Zhaodong Wang

doi:10.3390/ma11122591

Abstract

Aluminum alloys are widely used as first-choice materials for lightweight automotive applications. It is important that an alloy have a balance between strength and formability. In this study, the alloys were melted, cast, hot rolled, and cold rolled into 1 mm-thick sheets. The microstructure, mechanical properties, and precipitation behavior of Al–Mg–Si–1.0 wt %-Zn alloys with Mg/Si ratios of 0.5, 1, and 2 after solution treatment were studied using optical and electron microscopy, a tensile test, the Vickers hardness test, and differential scanning calorimetry. The results showed that a high density and number of Al–Fe–Si particles were observed in the matrix, thus causing the formation of more homogeneous and smaller recrystallized grains after treatment with the solution. In addition, a higher volume fraction of cubeND and P-types texture components formed during solution treatment. Also, a high r value and excellent deep drawability were achieved in the medium-Mg/Si-ratio alloy. The formation of denser strengthening precipitates led to a better paint-bake hardening effect in comparison with the other two alloys. Furthermore, the precipitation kinetics were enhanced by the addition of Si, and the addition of Zn did not alter the precipitation sequence of the Al–Mg–Si alloy. The dual-phase strengthening effect was not achieved in the studied alloys during paint-bake treatment at 175 °C.

Highlights

Precipitation hardening of an Al–Mg–Si alloy is an ideal choice for the automobile industry because of its high strength-to-weight ratio, good formability, excellent corrosion resistance, and low cost [1,2,3]
Increased strength in alloys is acquired by paint-bake hardening after the solution is heat-treated at 560 ◦ C and rapidly quenched to room temperature (RT) [4,5,6]
The influence of Zn content and different Mg/Si ratios on the microstructure, mechanical properties, and the precipitation behavior of Al–Mg–Si alloys was investigated in this study

Summary

Introduction

Precipitation hardening of an Al–Mg–Si alloy is an ideal choice for the automobile industry because of its high strength-to-weight ratio, good formability, excellent corrosion resistance, and low cost [1,2,3]. Increased strength in alloys is acquired by paint-bake hardening after the solution is heat-treated at 560 ◦ C and rapidly quenched to room temperature (RT) [4,5,6]. During paint-bake hardening, a large number of transition phases are formed in the matrix, resulting in a strengthening effect. It is reported that the generally accepted precipitation sequence of Al–Mg–Si alloys during artificial aging is as follows [7,8,9,10,11]: SSSS → solute clusters → GP (Guinier Preston) zones/pre-β00 →. The precipitate is semi-coherent with the Al matrix and contains less Si atoms than the GP zone [8]. The equilibrium phase β is FCC (Face center cubic) in structure It forms in plates with the composition Mg2 Si. Previous studies have

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