Predicting the constitutive behavior of semi-solids via a direct finite element simulation: application to AA5182

Abstract

The methodology of direct finite element (FE) simulation was used to predict the semi-solid constitutive behavior of an industrially important aluminummagnesium alloy, AA5182. Model microstructures were generated that detail key features of the as-cast semi-solid: equiaxed-globular grains of random size and shape, interconnected liquid films, and pores at the triple-junctions. Based on the results of over fifty different simulations, a model-based constitutive relationship which includes the effects of the key microstructure featuresfraction solid, grain size and fraction porosity-was derived using regression analysis. This novel constitutive equation was then validated via comparison with both the FE simulations and experimental stress/strain data. Such an equation can now be used to incorporate the effects of microstructure on the bulk semi-solid flow stress within a macro-scale process model.

Application of a Pore Fraction Hot Tearing Model to Directionally Solidified and Direct Chill Cast Aluminum Alloys

“…The key feature for predicting hot tearing using the Pore Fraction hot tearing model is the alloy's constitutive behaviour since this controls the development of the strain rate tensor within the mushy zone. As reported in [13], the modified Ludwik equation developed by Alankar and Wells [27 ] is used to simulate the constitutive behavior of the alloy at temperatures below the solidus temperature, while the constitutive behaviour between the solidus temperature (796.15 K (523˚C)) and the temperature for mechanical coalescence (875.15 K (602 ˚C)) is simulated based on microstructure and fraction solid according to a model proposed by Phillion et al [28] Above the temperature for mechanical coalescence, a low constant yield strength is specified, matching the yield strength values calculated with the model proposed by Phillion et al [28] at the temperature for mechanical coalescence.…”

Hot Tearing Susceptibility in DC‐Cast Aluminum Alloys

“…Although this methodology is relatively easy to implement in FE and has the advantage of minimizing false strain accumulation in the semi-solid, its main drawback is that there is no link to microstructural features. Recently, a new constitutive equation for semi-solid AA5182 has been proposed by Phillion et al [20] that takes advantage of the benefits of the Ludwik equation formulation within an FE simulation while also including microstructural features. The reader is referred to [20] for further details of the formulation of this constitutive law, along with its validation.…”

“…Recently, a new constitutive equation for semi-solid AA5182 has been proposed by Phillion et al [20] that takes advantage of the benefits of the Ludwik equation formulation within an FE simulation while also including microstructural features. The reader is referred to [20] for further details of the formulation of this constitutive law, along with its validation. In this law,…”

“…In order to investigate their occurrence, a new semi-solid constitutive law [20] for AA5182 that takes into account cooling rate, grain size and porosity has been implemented into a Direct Chill casting process model for round billets. The semi-solid stressstrain predictions provided by this new constitutive law as well as the effects of processing parameters were then examined to demonstrate the relationships between defect formation, microstructure, and processing variables.…”

Simulation of Semi-Solid Material Mechanical Behavior Using a Combined Discrete/Finite Element Method

“…Verne`de et al [17,18] have used this 2D granular approach to simulate the fluid flow caused by grain movement and solidification shrinkage in an Al-Cu alloy. Phillion et al, [19,20] using a similar approach based on 2D granular geometry, predicted the mechanical behavior of an equiaxed granular semisolid Al-Mg alloy.…”