Grain boundary fracture in Al–Li alloys

Abstract

In order to determine independently the roles of grain boundary (GB) δ-precipitates and shearable matrix δ′-precipitates in promoting low ductility in Al-Li alloys, three sets of samples of Al–10·7 at.-%Li–0·22 at.-%Mn were aged at 177°C, and the single edge notch slow bend Charpy toughnesses and yield strengths were determined. The first set of samples was from the as-quenched alloy, while the second and third were those previously peak aged, or overaged, and then reverted at 330°C to redissolve the matrix δ′ while leaving the GB δ. The results showed that the retained GB δ played a prominent role in promoting GB fracture, even in the absence of δ′. Comparison with high-strength AA 7375 aluminium alloy and with a γ/γ′ nickel-base superalloy either with or without GB carbides strongly supports the crucial role of GB precipitates in controlling ductility.MST/482