Application of the Rappaz-Drezet-Gremaud Hot Tearing Criterion to Welding of Aluminium Alloys

Hot tearing, a severe defect occurring during solidification is the conjunction of tensile stresses which are transmitted to the mushy zone by the coherent solid underneath and of insufficient liquid feeding to compensate for the volumetric change. The RDG (Rappaz Drezet Gremaud) criterion for the appearance of hot tears in metallic alloys is based upon a mass balance performed over the liquid and solid phases and accounts for the tensile deformation of the solid skeleton perpendicular to the growing dendrites and for the induced interdendritic liquid feeding. When tackling the problem of hot tearing in welding of aluminium alloys, the RDG criterion can be used at three levels of increasing complexity by: - ranking the alloy with regards to their sensitivity to hot cracking - studying the risk of hot tearing in the process using only the thermal field (thermal criterion), - and studying the influence of the mechanical behaviour of the mushy alloy on the risk of hot cracking (thermo-mechanical criterion). Each level is illustrated by an example dealing with laser beam welding. Nevertheless, one of the critical issues in the RDG approach is the definition of a coherency point which, in low-concentration alloys, corresponds to the bridging or coalescence of the primary phase. To tackle this aspect, a 2D granular model is presented together with preliminary results.