The Microstructure Evolution and Electrochemical Corrosion Behavior of 7A46 Aluminum Alloy in Different Quenching Conditions.

Yaru Liu,Haoru Yang,Jun Liang,Sheng Li,Qing Zeng,Lu Xing,Qinglin Pan

doi:10.3390/ma15020477

Abstract

The quenching condition of aluminum alloy can affect the mechanical property and corrosion resistance of the profile. This paper is aimed at the low quench sensitivity of aluminum alloys. Scanning electron microscopy and transmission electron microscopy were used to analyze precipitate behaviors of the 7A46 aluminum alloy under different isothermal cooling conditions and microstructure evolutions of quench-induced precipitations. The effect of the different isothermal time on the corrosion resistance of the alloy, and the relationship between microstructure and corrosion resistance after quenching were revealed through electrochemical impedance spectroscopy and potentiodynamic polarization tests. Results show that corrosion sensitivity of the quenching-aged alloy is much higher than that of the double-aged (DA) alloy, and the corrosion resistance of the quenched alloy decreases firstly and then increases. Due to the high density of the matrix precipitates, the increased content of the impurity element, the discontinuity of the grain boundary precipitates and the widening of the precipitates free zone, the most serious degree of corrosion performance among the quenched alloys is 295 °C at 800 s, and the self-corrosion potential and self-current density is −0.919 V and 2.371 μA/cm2, respectively.

Highlights

As the typical heat-treatable strengthening alloys, the performances including mechanical properties and corrosion resistance of Al-Zn-Mg-(Cu) alloys can be dramatically enhanced by solution treatments, quenching processes and ageing treatments [1]
Many studies have shown that the Al3 Zr particles form with the addition of Zr, which were coherent with the Al matrix and could hardly become the nucleation center of the quenched precipitates [6]
The quenched precipitates consume a large number of solute atoms, which decreases the precipitation of age-strengthening phases and results in a decline of the final mechanical properties of the studied alloy

Summary

Introduction

As the typical heat-treatable strengthening alloys, the performances including mechanical properties and corrosion resistance of Al-Zn-Mg-(Cu) alloys can be dramatically enhanced by solution treatments, quenching processes and ageing treatments [1]. Continuous cooling method refers to the quenching treatment of the alloy in the different quenching medium after solution, followed by artificial aging, which can obtain the microstructure and properties of the alloy continuously cooled at different quenching rates. The formation of quenching precipitates can consume a large number of adjacent quenching vacancies and solute atoms, leading to the formation of poor vacancies areas and solute atoms deficient regions. These phenomena lead to the decrease of precipitate density after the later ageing treatments, which dramatically weaken the mechanical properties of the alloys [7]. Li et al [9] revealed that the degree of recrystallization has a significant effect on the improvement of quenching sensitivity of the

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