Susceptibility of lithium containing aluminum alloys to cracking during solidification

Abstract

Hot cracking (namely, hot tearing for casting) is a phenomenon that occurs at elevated temperature close to the solidus of an alloying system. Normally, chemical composition has a significant impact on hot cracking susceptibility (HCS) when designing a new joining process or casting a new component. Here we quantified the HCS for Al–Li alloy systems as a function of alloying element additions using Kou's criterion, which treats the maximum |dT/dfs1/2| prior to 98% of solid fraction (fs1/2 = 0.99) as the sensitive index. In order to predict the HCS of industrial relevant alloys, non-equilibrium phase calculations were done using the Scheil Model coupled with a thermodynamic database for Al–Li, Al–Mg–Li, Al–Cu–Li, and Al–Mg–Cu–Li alloys. The HCS curves, histograms or maps were constructed based on the calculation results. It was shown that all Al–Li alloy systems exhibited typical "λ" shaped sensitive curves or maps. The Mg content had relatively less effect on the sensitive composition range than that of Cu or Li in the lower Mg containing Al–Mg–Cu–Li alloys. However, the indexes of all alloys reduce to negligible values at high solute concentrations. Taking into account that the Kou's criterion is a qualitative prediction, those predictions agree well with the experimental results of previous studies, validating the applicability of Kou's criterion for Al–Li alloys. In addition, the back diffusion during solidification may have an impact on the initiation or propagation of cracks, therefore future work including this complex kinetic should be done to further improve the accuracy of the predictions.