Integrated Approach for Prediction of Hot Tearing

Abstract

Shrinkage, imposed strain rate, and (lack of) feeding are considered the main factors that determine cavity formation or the formation of hot tears. A hot-tearing model is proposed that will combine a macroscopic description of the casting process and a microscopic model. The micromodel predicts whether porosity will form or a hot tear will develop. Results for an Al-4.5 pct Cu alloy are presented as a function of the constant strain rate and cooling rate. Also, incorporation of the model in a finite element method (FEM) simulation of the direct-chill (DC) casting process is reported. The model shows features well known from literature such as increasing hot-tearing sensitivity with increasing deformation rate, cooling rate, and grain size. Similar trends are found for the porosity formation as well. The model also predicts a beneficial effect of applying a ramping procedure during the start-up phase, which is an improvement in comparison with earlier findings obtained with alternative models. In principle, the model does not contain adjustable parameters, but several parameters are not well known. A full quanti-tative validation not only requires detailed casting trials but also independent determination of some thermophysical parameters of the semisolid mush. DOI: 10.1007/s11661-009-9941-y The Author(s) 2009. This article is published with open access at Springerlink.co

Effect of Main Elements (Zn, Mg, and Cu) on Hot Tearing Susceptibility During Direct-Chill Casting of 7xxx Aluminum Alloys

“…In the SKK criterion, [31] three possible phenomena may happen during the last stage of solidification. Firstly, the liquid flow can adequately compensate for the solidification shrinkage and thermal contraction, and therefore no cavities are formed.…”

“…Apart from experimental approaches, many non-mechanical and mechanical criteria have been proposed to predict hot tearing. [14,30,31] Suyitno et al [16] have evaluated eight commonly used criteria by implementing them into a thermomechanical model of DC casting. It was found that the RDG criterion [32] could predict the hot tearing susceptibility for all studied process parameters, although it was not able to accurately predict whether hot tears will form during DC casting.…”

“…It was found that the RDG criterion [32] could predict the hot tearing susceptibility for all studied process parameters, although it was not able to accurately predict whether hot tears will form during DC casting. [16] To address this problem, Suyitno et al [31] went further and proposed a microporosity-related hot tearing criterion, named SKK criterion (first letters of the authors' name). This criterion calculates the formation of pores during the last stage of solidification from the insufficient feeding in the mushy zone.…”

Multi-Physics and Multi-Scale Meshless Simulation System for Direct-Chill Casting of Aluminium Alloys

“…Once the stresses and strains in the material are known, the parameters related to the occurrence of casting defects can be calculated. The model used to calculate the micro-porosity in the material and the susceptibility of the material to hot tearing relies on the Suyitno-Kool-Katgerman model, which was developed specifically for use with numerical models of the casting process [13]. The model starts by stating the conservation equation for three phases, each associated with a volume fraction:…”

Numerical simulation of central shrinkage crack formation in a 234-t steel ingot

“…Finally, it is a combination of both non-mechanical and mechanical criteria, such as RDG (Rappaz-Drezet-Gremaud) and Suyitno criteria [13,14] , which investigate the pressure drop over the mush zone reaching a critical value for cavity nucleation or the microporosity exceeding a critical size. In this work, an experiment was carried on a 234-t heavy steel ingot where a shrinkage crack band was found in the ingot upper centerline.…”