Comparative Study of Microstructural and Corrosion Characteristics of Excimer Laser-Melted AA2124-T4 and AA6061-T4 Alloys

Abstract

A KrF excimer laser was introduced for laser surface melting (LSM) of the aluminium alloys AA2124-T4 and AA6061-T4. The microstructural and compositional analysis was conducted using SEM, low-angle XRD, and TEM; the corrosion behaviour of as-received (AR) and laser-treated (LT) samples was evaluated by electrochemical techniques and immersion test in a 3.5% NaCl solution. A melted layer consisting of a re-solidified layer with refined microstructure and dissolution of intermetallic particles (IMPs), and a thin film of aluminium oxides at the top, was formed after LSM for both alloys. The corrosion resistance of both alloys was improved after LSM. The results of immersion test showed different corrosion behaviour for LT AA2124 and LT AA6061. The delamination of the melted layer was observed for AA2124 but was not observed for AA6061 after exposure to 3.5% NaCl solution for 24 h. This was attributed to the formation of copper-rich segregation bands in the melted layer of AA2124 due to higher content of copper in AA2124 than AA6061. A significant number of micro-pores were present in the melted layer for AA2124 treated with high number of laser pulses, leading to the decrease of the corrosion resistance.