solidification cracks
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Materials ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 572
Author(s):  
Constantin Böhm ◽  
Martin Werz ◽  
Stefan Weihe

The range of available aluminum alloy powders for laser powder bed fusion (LPBF) is restricted to mainly Al–Si based alloys. Currently aluminum alloy powders, designed for lightweight application, based on Al–Mg (5000 series), Al–Si–Mg (6000 series), or Al–Zn–Mg (7000 series), cannot be processed by LPBF without solidification cracks. This has an impact on the potential of LPBF for lightweight applications. In fusion welding, solidification cracks are eliminated by using filler materials. This study aims to transfer the known procedure to LPBF, by supplementing EN AW-5083 (AlMg4.5Mn0.7) with AlSi10Mg. EN AW-5083 and two modifications (+7 wt.% and +15 wt.% AlSi10Mg) were produced by LPBF and analyzed. It was found that, in EN AW-5083, the solidification cracks have a length ≥200 µm parallel to the building direction. Furthermore, the solidification cracks can already be eliminated by supplementing 7 wt.% AlSi10Mg. The microstructure analysis revealed that, by supplementing AlSi10Mg, the melt pool boundaries become visible, and the grain refines by 40% relative to the base alloy. Therefore, adding a low melting point phase and grain refinement are the mechanisms that eliminate solidification cracking. This study illustrates a practical approach to eliminate solidification cracks in LPBF.


Author(s):  
Joseph N. Ghoussoub ◽  
Yuanbo T. Tang ◽  
William J. B. Dick-Cleland ◽  
André A. N. Németh ◽  
Yilun Gong ◽  
...  

AbstractThe susceptibility of nickel-based superalloys to processing-induced crack formation during laser powder-bed additive manufacturing is studied. Twelve different alloys—some of existing (heritage) type but also other newly-designed ones—are considered. A strong inter-dependence of alloy composition and processability is demonstrated. Stereological procedures are developed to enable the two dominant defect types found—solidification cracks and solid-state ductility dip cracks—to be distinguished and quantified. Differential scanning calorimetry, creep stress relaxation tests at 1000 °C and measurements of tensile ductility at 800 °C are used to interpret the effects of alloy composition. A model for solid-state cracking is proposed, based on an incapacity to relax the thermal stress arising from constrained differential thermal contraction; its development is supported by experimental measurements using a constrained bar cooling test. A modified solidification cracking criterion is proposed based upon solidification range but including also a contribution from the stress relaxation effect. This work provides fundamental insights into the role of composition on the additive manufacturability of these materials.


2022 ◽  
Vol 101 (1) ◽  
pp. 15-26
Author(s):  
ÖMER ÜSTÜNDAĞ ◽  
◽  
SERGEJ GOOK ◽  
ANDREY GUMENYUK ◽  
MICHAEL RETHMEIER ◽  
...  

The application of hybrid laser-arc welding (HLAW) for joining closed circumferential welds is a challenge due to the high risk of forming a defective overlap area with a shrinkage void or solidification cracks in the material thickness. A series of HLAW experiments were performed to understand the development of a faulty overlap area when closing the circumferential weld. Welding trials on flat specimens and pipe segments were supported by numerical analyses in which the thermomechanical behavior of the welds in the overlap area was investigated. Different process control strategies were tested, including variations in defocusing levels and the overlap length. The newly developed HLAW head, including laser optics with a motor-driven collimation system, made it possible to defocus the laser beam during welding without disturbing the stability of the welding process. High-level defocusing of the laser beam of more than 40 mm relative to the specimen surface with a resulting beam diameter of > 2.9 mm, and in combination with a short overlap length of 15 mm, was promising with respect to the formation of a desired cup-shaped weld profile that is resistant to solidification cracks.


Crystals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 902
Author(s):  
Benjamin Wahlmann ◽  
Dominik Leidel ◽  
Matthias Markl ◽  
Carolin Körner

In this work, we investigated the viability of established hot cracking models for numerically based development of crack-resistant nickel-base superalloys with a high γ′ volume fraction for additive manufacturing. Four cracking models were implemented, and one alloy designed for reduced cracking susceptibility was deduced based on each cracking criterion. The criteria were modeled using CALPHAD-based Scheil calculations. The alloys were designed using a previously developed multi-criteria optimization tool. The commercial superalloy Mar-M247 was chosen as the reference material. The alloys were fabricated by arc melting, then remelted with laser and electron beam, and the cracking was assessed. After electron beam melting, solidification cracks were more prevalent than cold cracks, and vice versa. The alloys exhibited vastly different crack densities ranging from 0 to nearly 12 mm−1. DSC measurements showed good qualitative agreement with the calculated transition temperatures. It was found that the cracking mechanisms differed strongly depending on the process temperature. A correlation analysis of the measured crack densities and the modeled cracking susceptibilities showed no clear positive correlation for any crack model, indicating that none of these models alone is sufficient to describe the cracking behavior of the alloys. One experimental alloy showed an improved cracking resistance during electron beam melting, suggesting that further development of the optimization-based alloy design approach could lead to the discovery of new crack-resistant superalloys.


Author(s):  
Dengkui Zhang ◽  
Aiping Wu ◽  
Yue Zhao ◽  
Jiguo Shan ◽  
Zhandong Wan ◽  
...  

The effects of Al–Mg wire replacing Al–Cu wire on the microstructure, microhardness and tensile properties of 2219 aluminum alloy tungsten inert gas (TIG)-welded joints were studied. Comparing joints with Al–Cu wire, the capping welds of joints with Al–Mg wire can be strengthened by the introduction of Mg-containing strengthening phase and the hardness can be significantly improved. However, for joints with Al–Mg wire, both the solidification cracks caused by inappropriate control of alloying element content and the continuous brittle phases at grain boundaries around the weld zone (WZ) can result in the reduced tensile properties. The crack-free weld can be obtained by adjusting the alloying system of WZ. Furthermore, the geometry of WZ also affected the tensile properties of joints with Al–Mg wire.


Author(s):  
Morteza Taheri ◽  
Seyed Farshid Kashani Bozorg ◽  
Ali Alizadeh ◽  
Mohsen Heydari Beni ◽  
Jafar Eskandari Jam ◽  
...  

Author(s):  
Marcel Gerstgrasser ◽  
Michael Cloots ◽  
Josef Stirnimann ◽  
Konrad Wegener

AbstractBased on SLM parameters from previous works, which guarantee fully dense and crack free CM247LC samples, multi laser beam strategies have been pursued to reduce residual stresses or rather distortion during LPBF processing. By using a second post heating and non-melting laser source with a defocused laser beam and lateral offset, cantilever distortion is reduced more than 7.5%, compared to the reference. Based on pre-tests with 9 different offset parameters, the optimum offset has been identified. Also, an upper limit for the laser power of 65 W is identified for the second heat laser beam with a spot diameter of 380 μm, to avoid re-melting and creating new defects. A theoretical “two bar model,” to explain the residual stress behavior and reduction with multi laser beam offset strategy during the LPBF process, is presented. Furthermore, re-melting cracks, defects, and microstructure are analyzed in conjunction with the second defocused offset laser, in case of a 200 W laser power, an increased scan speed of 1300 mms/s, and a reduced hatch distance. Secondary electron signal (SE) images of re-melting cracks are analyzed and compared to SE-image of hot cracks (solidification cracks). Based on electron backscatter diffraction (EBSD), the results of the microstructure from the last mentioned multi laser beam approach, which creates re-melting cracks, are presented and analyzed.


2021 ◽  
pp. 68-74
Author(s):  
Вафик Харара

Tungsten inert gas (TIG) welding had been applied to produce four double-V butt welded joints performed on thick plates made from 6082-T6 aluminum alloy. The thicknesses of the plates are 18, 45, 60, and 80mm.This type of aluminum alloy is very sensitive to heat due to its high conductivity and high thermal expansion coefficient. Heat from TIG welding reduces the strength of the cited welded plates in the welding zone and in the heat affected zone (HAZ) and favorites the formation of porosities and solidification cracks in the welded joints. Porosities and solidification cracks are the most frequent imperfection that appear in this type of welded joints and they are often the reason which prevent them to comply with the requirements of the BS EN ISO 10675-2: 2017 Non destructive testing of welds: Acceptance levels for radiography testing-Aluminium and its alloys, and of the BS EN ISO 23277: 2015 penetrant testing of welds –Acceptance levels. This article represents the type of the filler metal that used and the welding parameters that applied to perform TIG welding of the cited thick plates in order to get welded joints that are free from porosities and solidification cracks as confirmed by X-ray radiography and by red dye penetrant testing of these welded joints.


Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 267
Author(s):  
Lei Huang ◽  
Xizhang Chen ◽  
Sergey Konovalov ◽  
Arshad Noor Siddiquee ◽  
Gang Lu ◽  
...  

In this work, a welding solidification crack sensitivity test platform was established to study the effect of wire feeding speed (WFS) on solidification crack sensitivity during cold metal transfer (CMT) welding for AA6061 aluminum alloy. The test results show that as the WFS increased from 4 m/min to 5.5 m/min, the sensitivity of the solidification cracks also increased. With a further increase in the value of the WFS, the crack sensitivity decreased and eventually ceased to exist. A new perspective of the microstructure and crack propagation mechanics model was applied to understand the effect of WFS on solidification cracks. With the use of scanning electron microscopy (SEM) and a high-speed camera, it was found that as the WFS increased from 4 m/min to 5.5 m/min, the microstructure of the grain size changed from bigger to smaller, and the stability of the crystal microstructure was reduced. The crack propagation mechanics model was changed, which promotes crack propagation, increasing by 233%. When the WFS continued to increase beyond 5.5 m/min, the size of the crystal structure changed from small to big, the stability of the crystal microstructure was increased, the crack generation was suppressed, and the cracking rate was significantly reduced.


Metals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 35
Author(s):  
Filippo Belelli ◽  
Riccardo Casati ◽  
Martina Riccio ◽  
Alessandro Rizzi ◽  
Mevlüt Y. Kayacan ◽  
...  

The number of available materials for Laser Powder Bed Fusion is still limited due to the poor processability of many standard alloys. In particular, the lack of high-strength aluminium alloys, widely used in aerospace and automotive industries, remains a big issue for the spread of beam-based additive manufacturing technologies. In this study, a novel high-strength aluminium alloy for high temperature applications having good processability was developed. The design of the alloy was done based on the chemical composition of the widely used EN AW 2618. This Al-Cu-Mg-Ni-Fe alloy was modified with Ti and B in order to promote the formation of TiB2 nuclei in the liquid phase able to stimulate heterogeneous nucleation of grains and to decrease the hot cracking susceptibility of the material. The new Al alloy was manufactured by gas atomisation and processed by Laser Powder Bed Fusion. Samples produced with optimised parameters featured relative density of 99.91%, with no solidification cracks within their microstructure. After aging, the material revealed upper yield strength and ultimate tensile strength of 495 MPa and 460 MPa, respectively. In addition, the alloy showed tensile strength higher than wrought EN AW 2618 at elevated temperatures.


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