Development of Stress During the Solidification of an Aluminium Alloy: Experimental and Numerical Assessment of Influence of Elasticity Parameters during Solidification

摘要

Calculation of stresses and strains during solidification processes has a major interest to model thermome-chanical coupling and predict hot cracking. The validity of modelling depends on knowledge of the mechanical properties of alloys at temperatures close to the solidus and even in the solidification interval. The elasto-visCoplastic behaviour of an Al-4.5% Cu-0.3%Mg-Ti alloy was identified at temperatures concerned with hot cracking using isothermal tensile/ compression tests. The tests were performed on a Schenck fatigue machine with a high temperature extensometer so that Young's modulus could be deduced from experiments. An apparatus to measure uniaxial tensile stress in a solidifying constrained bar was designed. The elasto-viscoplastic properties were used to model these experiments with the finite element code Thercast3. The evolution of calculated and measured loads during solidification could then be compared. The calculated stress appeared to be up to five times higher than the experimental one. This is explained by a decrease in the mechanical properties of the alloy induced by the weakening of the solid skeleton when solidifying under tensile stress as compared to the one solidified without stress.