The high fusion welding hot cracking sensibility of the next-generation alloy is the key technological difficulty that hinders its widely application in the aeronautic and astronautic industry. A critical review of the fusion welding hot cracking from the perspective of basic mechanism and the experimental research of typical materials was presented in this article. The fusion welding hot cracking phenomena include solidification cracking (occurs within the fusion zone) and liquidation cracking (occurs at the interface between fusion zone and partial melting zone). The formation factors of the fusion welding hot cracking include alloying composition, welding thermal cycle and thermal stress. Based on the comprehensive understanding of the formation mechanism of the fusion welding hot cracking, the relative research progress in the field of aluminum alloys, magnesium alloys, advanced high strength steel and nickel alloys was summarized. The establishment of the quantitative criterion that involves the effects of complicated multi-component and the morphology of the dendrite on the cracking sensibility is the key development direction. Optimizing the alloying composition of the base metal or filler metal, adding nucleanting agent or auxiliary facilities are the practical method for restraining the fusion welding hot cracking. Conducting the research on the mechanism and restraining method of the fusion welding hot cracking helps to solve the difficulty of the next generation alloys processing, which can realize their application in the field of aeronautic and astronautic industry.
李红, 闫维嘉, 张禹, 杜文博, 栗卓新, MARIUSZBober, SENKARAJacek. 先进航空材料焊接过程热裂纹研究进展[J]. 材料工程, 2022, 50(2): 50-61.
Hong LI, Weijia YAN, Yu ZHANG, Wenbo DU, Zhuoxin LI, Bober MARIUSZ, Jacek SENKARA. Research progress of hot crack in fusion welding of advanced aeronautical materials. Journal of Materials Engineering, 2022, 50(2): 50-61.
Crack will occur if stress pull apart two parallel plates separated by a thin liquid film as to the strength of semi-solid metals. Viscosity and wetting angle are neglected Application: liquation crack, solidification crack
Williams and Singer (1968)
σfr-fracture stress; A-a constant dependent on the grain size and the dihedral angle; G-shear modulus; γ-effective fracture surface energy; VL-volume of liquid; ν-Poisson’s ratio; D-grain size
Modified from the Griffith model. The equation has been modified for the contribution of grain boundary sliding that aids the liquid crack growth Application: liquation crack, solidification crack
Dickhaus et al. (1993)
Fz-the force required to increase the thickness of the liquid film from b1to b2; η-dynamic viscosity; R-radius of a plate; t-the time required to increase the film thickness from b1 to b2; b-film thickness; fs-fraction of solid; d-average thickness of a solidifying grain
The effect of viscosity on the critical force is considered Application: solidification crack
Lahaie and Bouchard (2001)
σfr-fracture stress; η-dynamic viscosity; b-film thickness; ε-strain; m-the microstructure parameter, which is 1/3 for equiaxed and 1/2 for columnar structure; fs-fraction of solid
Expansion of Dichaus’ criterion. By changing the coefficient m, it can be applied to equiaxed or columnar crystal structures Application: liquation crack, solidification crack
Pr-reserve of plasticity; S-the difference between the average integrated value of the elongation to failure and the linear shrinkage in the brittle temperature range; ΔTbr-brittle temperature range
In the range of brittle temperature, the time when the fracture elongation is lower than the linear shrinkage is the sensitive period for cracking Application: liquation crack, solidification crack
Magnin et al. (1996)
εθθ-the maximum principle plastic strain at the solidus temperature; εfr-the measured strain at a temperature close to the solidus
Cracks occur when the maximum principal strain is greater than the fracture strain. The ratio of their HCS is hot crack sensitivity Application: liquation crack, solidification crack
Strain rate-based criteria
Tbr-brittle temperature range; εres-reserve strain; -reserve strain rate; Dmin-minimum fracture strain in ΔTbr；-minimum fracture strain rate in ΔTbr；εfree-free linear contraction strain; -free linear contraction strain rate; εapp-actual strain in the solidifying body and strain rate; -actual strain rate in the solidifying body
The higher the at which the hot cracking occurs, the worse the solidifying body configuration in relation to hot tearing Application: liquation crack, solidification crack
Rappaz et al. (1999)
G-thermal gradient; λ2-secondary dendrite arm spacing; β-volumetric solidification shrinkage factor; μ-viscosity; ΔT0-vulnerable temperature range; VT-growth velocity of dendrites; A and B-depend only on the nature of the alloy and its solidification path; Pmax-critical cavitation pressure
Considered both uniaxial tensile deformation and shrinkage feeding Cracking occurs when the strain rate is higher than the maximum strain rate that the mushy zone can be sustainable Application: solidification crack
Hot cracking occurs when the replenishment liquid flow required for solidification volume shrinkage is greater than the maximum liquid flow that can pass through the porous Application: solidification crack
SPV-maximum volumetric flow rate per unit volume; SRG-velocity of volumetric solidification shrinkage; f1-volume liquid fraction; λ2-secondary dendrite arm spacing; PS-effective feeding pressure; c-tortuousity constant of dendrite network; η-dynamic viscosity; L-length of porous network; ρ-average density; V-volume element of the solidifying mush with constant mass; t-time
Kool and Katgerman(2009)
d-cavity size; acrit-critical size; c-ratio of the lattice constant to the atomic radius; fv-cavity fraction; dg-grain size; γ1-surface energy of the liquid phase; E-Young’s modulus of the semi-solid; σ-tensile stress
When the cavity size is larger than the critical size, the liquid phase is not filled enough to form a hot crack Application: liquation crack, solidification crack
εlocal-local strain; T-temperature; β-solidification shrinkage; fs-solidification shrinkage; t-time; νz-intergranular liquid flows at the velocity νz in the negative z direction
Cracking can initiate from preexisting nucleation sites or the free surface and propagate if the separation rate of two neighboring grains caused by tensile deformation, subtracted by their growth rate toward each other, exceeds the feeding rate of liquid along the grain boundary Application: liquation crack, solidification crack
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