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

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Vol. 47; no. 8; pp. 4217 - 4225
• Main Authors: Dou, Ruifeng, Phillion, A. B.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.08.2016; Springer Nature B.V
• Subjects: Aluminum alloys; Aluminum base alloys; Binary systems; Casting; Characterization and Evaluation of Materials; Chemistry and Materials Science; Criteria; Deformation; Direct chill casting; Finite element analysis; Materials Science; Mathematical analysis; Mathematical models; Metallic Materials; Metallurgy; Nanotechnology; Porosity; Shrinkage; Structural Materials; Surfaces and Interfaces; Tearing; Tensile strength; Thin Films; Shrinkage Porosity; Thermal Gradient; Casting Speed; Mushy Zone; Direct Chill Casting
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-016-3590-8

Hot tearing susceptibility is commonly assessed using a pressure drop equation in the mushy zone that includes the effects of both tensile deformation perpendicular to the thermal gradient as well as shrinkage feeding. In this study, a Pore Fraction hot tearing model, recently developed by Monroe and Beckermann (JOM 66:1439–1445, 2014 ), is extended to additionally include the effect of strain rate parallel to the thermal gradient. The deformation and shrinkage pore fractions are obtained on the basis of the dimensionless Niyama criterion and a scaling variable method. First, the model is applied to the binary Al-Cu system under conditions of directional solidification. It is shown that for the same Niyama criterion, a decrease in the cooling rate increases both the deformation and shrinkage pore fractions because of an increase in the time spent in the brittle temperature region. Second, the model is applied to the industrial aluminum alloy AA5182 as part of a finite element simulation of the Direct Chill (DC) casting process. It is shown that an increase in the casting speed during DC casting increases the deformation and shrinkage pore fractions, causing the maximum point of pore fraction to move towards the base of the casting. These results demonstrate that including the strain rate parallel to the thermal gradient significantly improves the predictive quality of hot tearing criteria based on the pressure drop equation.