A Quest for a New Hot Tearing Criterion

Abstract

Hot tearing remains a major problem of casting technology despite decades-long efforts to develop working hot tearing criteria and to implement those into casting process computer simulation. Existing models allow one to calculate the stress-strain and temperature situation in a casting (ingot, billet) and to compare those with the chosen hot tearing criterion. In most successful cases, the simulation shows the relative probability of hot tearing and the sensitivity of this probability to such process parameters as casting speed, casting dimensions, and casting recipe. None of the existing criteria, however, can give the answer on whether the hot crack will appear or not and what will be the extent of hot cracking (position, length, shape). This article outlines the requirements for a modern hot tearing model and a criterion based on this model as well as the future development of hot tearing research in terms of mechanisms of hot crack nucleation and propagation. It is suggested that the new model and criterion should take into account different mechanisms of hot tearing that are operational at different stages of solidification and be based on fracture mechanics, i.e., include the mechanisms of nucleation and propagation of a crack.

Process Optimization of Dual-Laser Beam Welding of Advanced Al-Li Alloys Through Hot Cracking Susceptibility Modeling

“…It is commonly assumed that the dendrites start to bridge together when the solid fraction reaches approximately 98 pct if the eutectic temperature is not yet reached. [5,15,16] Therefore, the integral limits for the A parameter in Eq. [5] are from the point where the solid fraction f s = 0.98, i.e., the so-called coherency temperature, to the liquidus temperature.…”

Influence of zirconium and scandium on the microstructure, tensile properties, and hot-tearing susceptibility of Al-2WT%Cu-based alloys /

“…Based on the alloy microstructure shown in Figure 6.7, it will be observed that the severity of shrinkage porosity and hot cracking may be reduced significantly upon the hot-tearing crack initiates from a pore or a series of pores in conditions of non-uniform thermal contraction of the coherent dendrites. 94 Such parallelism may also be explained by the deteriorating effect caused by the limited feedability and the diminished permeability of the mushy zone leading to the formation of high levels of porosity and to the difficulties It should be mentioned that the Bl Si-alloy is not covered by this equation. These results which were illustrated in the preceding three figures may help to explain the beneficial role of the grain refining additions, namely Zr-Ti and Ti, in reducing the hot-tearing susceptibility of the Al-2wt%Cu base alloy.…”

Cold cracking in DC-cast high strength aluminum alloy ingots: An intrinsic problem intensified by casting process parameters

“…High cooling rates and non-equilibrium solidification conditions of the DC-casting result in the formation of nonequilibrium eutectics and intermetallics, which mainly precipitate on the grain boundaries and interdendritic spaces during final stages of solidification [2,3]. The formation of such phases coincides with the appearance of thermal stresses when the dendritic grains start to form a coherent network [4]. Due to their low melting point, the non-equilibrium eutectics provide potential nucleation sites and propagation paths for hot cracking (cracking above the solidus) while they are still in the liquid state.…”