Validation of a new hot tearing criterion using the ring mould test

Abstract

Abstract. Hot tear is one of the most serious defect which a casting can suffer. It represents a major limitation to the production of foundry cast parts and to the productivity of continuous casting processes such as the direct chiil casting of aluminium alloys. As an exemple, the starting phase of the direct chili casting process remains particularly critical for some aluminium alloys because of their high propensity to develop either hot tears which initiate at non zero liquid fraction, or coid cracks which nucleate and grow exclusively in the solid metal. In order to validate a new hot tearing criterion recently proposed by Rappaz and Drezet [1), instrumented ring mould tests were carried out with aluminium alloys of different composition and further on analysed from a thermal, mechanical and microstructural point of view. The thermal field obtained in the test was determined with the help of an inverse method using five temperature histories measured at different locations and the stress build-up was computed with a transient thermomechanical model implemented in the finite element package Abaqus. Deformation in the solid was assumed to obey a viscoplastic law and the cooling conditions were those deduced by the inverse method. The new hot tearing criterion [1] based on the ability of the interdendritic flow of liquid to compensate for the thermally induced deformation of the roots of columnar dendrites, allowed the calculation of the maximum strain rate that the roots of the dendrites can undergo without initiation and/or propagation of hot tears. After implementation in the numerical FEM model of the ring mould test, the hot tearing criterion predicted the occurrence of tears precisely in the region where hot cracks were observed after the test. More generally, when implemented in thermomechanical models of casting processes, the present hot tearing criterion would be very helpful in diminishing the cracking tendency.

Hot Tearing Sensitivity of Al-Mg-Si Alloys Evaluated by X-Ray Microtomography After Constrained Solidification at High Cooling Rate

“…Many techniques have been developed to assess hot tearing susceptibility [3]. The ring mould testing is frequently used to evaluate the hot tearing tendency of aluminum alloys [3,4]. The mould consists of a ring and a core.…”

Influence of solidification conditions on the castability of nickel-base superalloy IN792

“…The remaining thin film of liquid along the grain boundaries has no sufficient resistance against stresses and strains due to the volume contraction associated with the liquid-to-solid phase transformation in the alloy and the thermal contraction in the solid. [10][11][12][13] At the WTM Institute, a number of factors that influence solidification cracking have been studied in the past, such as overall alloy composition, [7,14] content of grain boundary elements such as B and Zr, [15] and grain boundary misorientation. [16] It was found that common explanations based on freezing range or amount of eutectic melt are not able to describe the effects observed.…”