Microstructure and corrosion properties of AA2091-T3 in weld heat affected zone

Abstract

The microstructure and corrosion behaviour of an AA2091-T3 alloy weld heat affected zone (HAZ) were investigated using differential scanning calorimetry and electrochemical measurements in 3·5% NaCl solution. The δ′ phase was precipitated during the welding cooling process. The amount of δ′ precipitates depends on the peak temperature of the weld thermal cycle. The quantity of Guinier–Preston (GP) zones was related to the duration of natural aging. Variation of pitting potential of the weld HAZ was due to the lithium content in the matrix. The increasing dissolution of GP zones and δ′ phase was accompanied by increasing lithium contents in the matrix and caused a negative shifting of pitting potential. The region containing the lowest quantity of GP zones and δ′ phase had the lowest pitting potential. The higher the peak tem perature of the weld thermal cycles the more precipitation of T₂ phase on grain boundaries occurs. These T₂ phases can cause severe intergranular exfoliation corrosion.