The maximum stress at the solidus temperature of the AZ31 alloy was measured to be 13 MPa. obtained a relation for the maximum tensile stress as a function of temperature. As-cast specimens were reheated and pulled in a Gleeble machine. reported measurements of the constitutive behavior of an AZ31 magnesium alloy in the semisolid stage. This study relied on crude estimates of the mechanical properties. Recently, an attempt has been made to numerically simulate the deformations and stresses during permanent mold casting of an AZ91 magnesium alloy in order to predict hot tears. The availability of mechanical properties that are suitable for advanced stress modeling is even more limited for magnesium alloys. At such high solid fractions, liquid feeding is no longer possible and fracture of the mush will lead to the formation of an open hot tear. Above a solid fraction of 0.9, the strength increased more rapidly because the grains start to coalesce and form a coherent solid network. The strength of the mush was found to increase gradually for solid fractions between 0.5 and 0.9. Considerable insight into the coherency properties of the mush was obtained. These comparisons showed that advanced stress models are able to predict the variation of the tensile stress with strain and solid fraction until fracture. Recently, Mathier and co-workers performed a detailed comparison between measured and predicted forces in the mush during solidification of dilute aluminum alloys. Most progress in determining the mechanical properties needed in advanced stress models has been made for aluminum alloys. Tests in which specimens are reheated and partially remelted suffer from the fact that the microstructure and the solid fraction-temperature relationship are generally not the same as during solidification from the melt. Measurements of the relevant mechanical properties of metal alloys in the semisolid state are relatively limited. In this regard, the coherency and strength properties of the mush, including coalescence of the solid over a certain range of solid fractions, are particularly important. Such modeling requires the knowledge of the mechanical properties of a metal alloy over the entire range of temperatures and strain rates encountered during casting. In these models, the semisolid mush is treated as a viscoplastic, compressible porous medium, where the mechanical behavior depends on the local volume fraction of solid among other factors. Based on the comparison of measured and predicted stresses, it is also shown that coupling of the stress model to feeding flow and macrosegregation calculations is needed in order to accurately predict stresses in the presence of hot tearing.ĭ uring the past decade, advanced stress models have been developed to simulate the deformations occurring during casting of metal alloys and to ultimately predict the occurrence of hot tears (for example, References 1 through 5). In the presence of hot tearing, the measured stresses are generally overpredicted, which is attributed to the lack of a fracture model for the mush. It is found that coherency of the semisolid mush starts at a solid fraction of about 0.5 and that the maximum tensile strength for the Mg-1 and 9 wt pct Al alloys at their final solidification temperatures is 1.5 and 4 MPa, respectively. In the absence of hot tearing, the simulation results show reasonably good agreement with the measurements. Force measurements from castings that did not hot tear, together with estimates from data found in the literature, are used to obtain the high-temperature mechanical properties needed in the stress model. A viscoplastic stress model is used to predict contraction forces measured during casting of two binary Mg-Al alloys.