Microstructure and corrosion properties of AA2091-T3 in weld heat affectedzone

The microstructure and corrosion behaviour of at? AA2091-T3 alloy weld hear affected zone (HAZ) were investigated using differential scanning calorime try and electrochemical measurements iii 3.5%NaCl solution. The delta' phas e was precipitated during the welding cooling process. The ai amount of del ta' precipitates depends on the peak temperature of the,veld thermal cycle. The quantity of Guinier-Preston (GP) zones,vas related to the duration of natural aging. Variation of pitting potential of the weld HAZ was due to th e lithium content in the matrix. The increasing dissolution Of GP zones and delta' phase was accompanied by increasing lithium contents in the matrix and caused a negative shifting of pitting potential. The legion containing the lowest quantity of GP zones and delta' phase had the lowest pitting pot ential. The higher the peak temperature of rite weld thermal cycles the mol e precipitation of T-2 phase on gl ain boundaries occurs. These T-2 phases can cause severe intergranular exfoliation corrosion.