Microstructure and corrosion behaviour of precipitation hardened and thermo-mechanical treated high strength Al-12Zn-3Mg-2.5Cu alloy

Abstract

Purpose

The purpose of this paper is to study the corrosion behaviour of Al-12Zn-3Mg-2.5Cu alloy by cast, precipitation hardening and non-isothermal step rolling cum cold/cryo rolling (−80 and −196°C) in 3.5 per cent NaCl solution.

Design/methodology/approach

Aluminium alloy with high alloying concentration (Zn: 12 per cent, Mg: 3 per cent, Cu: 2.5 per cent) was prepared by squeeze casting method with controlled process parameters. The cast alloy was solution treated at 450°C for 24 h and aged at 120°C with varying time intervals. Initially, the alloy also underwent non-isothermal step rolling from 6 mm to 3 mm at 400-100°C at the step of 100ºC with 15% reduction in thickness. Non-isothermal rolled alloy (3 mm thickness) was the starting material for further rolling at three different temperatures, such as room temperature, −80 and −190°C with 85 per cent reduction. Microstructural evolution during precipitation and thermo-mechanical processing was studied with the help of optical microscopy and electron microscopy. A potentio-dynamic polarization study was performed to evaluate the corrosion behaviour of Al-12Zn-3Mg-2.5Cu alloy processed in different conditions in 3.5 per cent NaCl solution.

Findings

There is a distinct evidence that the alloy exhibits varying corrosion resistance by changing its structural features. In fact, the alloy with ultra-fine grained structure exhibits good corrosion resistance than that of alloy in cast. This is attributed to a greater grain boundary region with high dislocation density, and plastic strain adversely affects the corrosion resistance.

Originality/value

The results obtained by this investigation help in understanding the effect of precipitation hardening and non-isothermal step rolling cum cold/cryo rolling (−80 and −196°C) on corrosion behaviour.

Citation

Ravikumar, V.V. and Kumaran, S. (2018), "Microstructure and corrosion behaviour of precipitation hardened and thermo-mechanical treated high strength Al-12Zn-3Mg-2.5Cu alloy", Anti-Corrosion Methods and Materials, Vol. 65 No. 1, pp. 79-86. https://doi.org/10.1108/ACMM-04-2017-1780