Effects of heat treatment parameters on microstructural changes and corrosion behavior of Al 7075 Alclad alloy

Abstract

Purpose

The purpose of this paper is to investigate the microstructural changes and stress corrosion cracking behavior via two‐stage stressing u‐bent tests for T6 and T73 tempers of Al 7075 Alclad alloy.

Design/methodology/approach

Study was made of the effects of heat treatment; two‐stage stressing u‐bent, metallography, scanning electron microscopy, energy dispersive spectroscopy were employed.

Findings

The results showed that the T6 heat treatment formed some very fine transgranular and coarse intergranular precipitates containing two compositions of (Fe/Cu/Si‐rich) and (Mg/Si‐rich) phases. The T73 treatment also precipitated some fine transgranular precipitates and coarse intermetallics with a (Fe/Cu‐rich) composition. In T6‐treated samples, stress corrosion cracking (SCC) occurred after 155 days due to the high susceptibility of the grain boundaries. In T73‐treated samples, the SCC did not occur even after 210 days. The dissolution of the Alclad layer in the corrosive media increased pH values and left the sample in the passivation region, protecting the sample from further corrosion attack.

Originality/value

Based on microstructural and SCC resistance properties obtained by heat treatments, the T73 heat treatment with a tempering temperature of 107°C for seven hours as the first step and 170°C for 19 hours as the second step can be recommended for Al 7075 Alclad sheets.

Citation

Askari‐paykani, M., Meratian, M., Shayan, M. and Raeissi, K. (2012), "Effects of heat treatment parameters on microstructural changes and corrosion behavior of Al 7075 Alclad alloy", Anti-Corrosion Methods and Materials, Vol. 59 No. 5, pp. 231-238. https://doi.org/10.1108/00035591211265523