Quantitatively Comparing 3D Discrete Element Method Simulations With Drained Compression Experiments of the Semi-solid Deformation of Al-Cu Alloys

Modeling the deformation behavior of semi-solid alloys with a percolating solid network is crucial for understanding the rheological phenomena in advanced pressurized casting processes such as die casting, squeeze casting, twin-roll casting, and semi-solid forging. However, the coupled mechanical behavior between grain rearrangement and individual grain deformation is complex; hence, the development of a suitable computational mechanics approach and a constitutive modeling framework is challenging. Motivated by recent in-situ synchrotron X-ray imaging studies reporting that semi-solid deforms predominantly by the intergranular rearrangement of primary aluminum crystals, the present study used the particulate discrete element method in three dimensions to virtually create and compress two numerical assemblies of primary aluminum grains with volumetric solid fractions of 82 and 60 pct. The Burgers contact model was introduced to model the plastic deformation of globular grains in response to high-temperature compression. The mechanical response of each simulated grain assembly was compared with that in a drained die compression experiment with the same boundary conditions. In this study, the one-dimensional normal compression line from the critical state soil mechanics framework is demonstrated to be a useful concept for understanding the rheological behavior of the semi-solid as a function of the initial solid fraction, temperature, and global strain rate.