Estimation of solidification cracking susceptibility in Al–Si–Cu alloy weld: effects of anisotropic permeability and deformation orientation

Abstract

Weld solidification cracking susceptibility (SCS) was evaluated using an analytical model developed considering the anisotropic permeability (i.e., permeability which is different in directions parallel and perpendicular to the primary dendrite arms) and deviation of the imposed deformation from the normal direction with respect to the primary dendrite arm (ϕ). The model was investigated for Al–Si–Cu alloys in the solid fraction range from 0.87 to 0.94. Low Si- high Cu content alloys showed the maximum SCS due to variation in the physical properties of weld pool, i.e., viscosity, solidification range and solid fraction as a function of temperature. Decrease in deviation of the deformation direction (ϕ) led to increase in the SCS. Using the anisotropic permeability as a function of the primary dendrite arm spacing (λ1) led to a change in the peak position of shrinkage pressure depression towards the high Si-high Cu content alloys. Arc oscillation imposed a dual impact on the SCS of weld: (i) increased the SCS by enhancement of the base metal dilution, i.e., adding more Cu into the weld pool and (ii) decreased the SCS by refining the weld microstructure and twisting the grain boundaries which in turn changed the deformation direction on the grain boundaries. Results of the weldability test on Al–Cu sheets welded using Al–Si filler metal were in good agreement with the model prediction.