Defects and Properties of Cast Metals: Porosity & Cracking
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Solidification Committee
Program Organizers: Lang Yuan, University of South Carolina; Brian Thomas, Colorado School of Mines; Peter Lee, University College London; Mark Jolly, Cranfield University; Alex Plotkowski, Oak Ridge National Laboratory; Charles Monroe, University of Alabama Tuscaloosa
Tuesday 2:00 PM
February 25, 2020
Room: 17B
Location: San Diego Convention Ctr
Session Chair: Lang Yuan, University of South Carolina; Chu Lun Alex Leung, University College London
2:00 PM Invited
Resolving Pore Evolution Mechanisms During Laser Powder Bed Fusion Additive Manufacturing by Multi-modal Imaging: Chu Lun Alex Leung1; Sebastian Marussi1; Lorna Sinclair1; Samuel Clark2; Yunhui Chen1; Leigh Stanger3; Jon Willmott3; Robert Atwood4; Andrew Bodey4; Margie Olbinado5; Alexander Rack5; Peter Lee1; 1University College London; 2University College, London; 3University of Sheffield; 4Diamond Light Source Ltd; 5European Synchrotron Radiation Facility
Pore evolution mechanisms in laser powder bed fusion (LPBF) additive manufacturing depend on many factors, ranging from materials chemistry to processing parameters, and hence are not well-understood. Here, we capture the pore dynamics inside single-layer melt tracks during PBF of virgin and oxidised powders using high-speed synchrotron X-ray, optical, and infra-red imaging. This is done for both overhang and multi-layer build conditions. Our results show that pores can form during melting and during solidification. Gas pores can (1) migrate in the molten pool via Marangoni convection, (2) grow in the expense of the others via coalescence, (3) dissolve into the solid solution or (4) eject as spatter during laser re-melting, (5) and precipitate into the melt pool or (6) lead to bubble bursting during cooling. Our results confirm that their size, morphology, and location are strongly depending on the processing parameters, shedding light onto pore formation mechanisms in LPBF.
2:30 PM
Assessment of Grain Refinement on Hot-tearing of New Multicomponent Al-Cu Alloys: Adrian Sabau1; Seyed Mirmiran2; Christopher Glaspie2; Shimin Li3; Diran Apelian3; Amit Shyam1; Andres Rodriguez4; J. Haynes1; 1Oak Ridge National Laboratory; 2Fiat Chrysler Automobiles (FCA) North America, LLC.; 3Worcester Polytechnic Institute; 4Nemak Monterrey
Hot-tearing is a major casting defect that is difficult to overcome, especially for multicomponent Al alloys used for cylinder head castings as Al-Cu alloys are well known to be prone to hot-tearing in permanent mold casting. In this study, hot-tearing indices were evaluated for a new multicomponent Al-Cu alloy family using two different permanent molds in order to ensure an adequate and accurate characterization of the hot-tear resistance. The relationship between the two hot-tearing indices, which are estimated by visually examining the cracking severity, and the load at solidus was investigated. The Cu composition was varied from approximately 5 to 8 wt.%. Based on the hot-tearing evaluation, it was found that higher Cu levels acted as an effective grain refiner for the non-grain refined alloys and that additional grain refining via Al-5Ti-1B master alloy significantly reduces the hot-tearing susceptibility at Cu contents greater than 7.3 wt.%.
2:50 PM
How to Prevent Gas Porosity Defects in Castings of Stator Housing in Grey Cast Iron: Izudin Dugic1; 1Linnaeus University
Grey cast iron is one of the easiest metals to cast in a foundry, and of ferrous metals, it has the lowest pouring temperature, high fluidity and very low shrinkage during the transformation from the liquid to solid phase. One of the disadvantages of this grade of cast iron is the presence of the different types of defects produced in green sand casting. Cast defects are, at a higher proportion, caused by evolution of gases. Pinholes and blowholes are major casting defects caused by gases. This experimental work has focused on reducing gas defects on casting component, stator housing, at a production scale using the green sand casting process. The casting component produced was strongly affected by gas defects. A series of simulations were performed using the casting simulation program MagmaSoft® in order to investigate the solidification characteristics as well as the porosity formation in the casting component.
3:10 PM
Bubble Induced Convection During Dendritic Solidification: Seyed Amin Nabavizadeh1; Mohsen Eshraghi2; Sergio Felicelli1; 1University of Akron; 2Department of Mechanical Engineering, California State University
The Pore Formation and Mobility Investigation (PFMI) at the International Space Station revealed that the Marangoni convection caused by the presence of bubbles could affect the microstructure formation. The experiment provided information on the bubble movement and morphological evolution during remelting and directional solidification under microgravity condition for succinonitrile (SCN)-water binary alloy. In this work, a three-dimensional lattice Boltzmann (LB)-Cellular automaton (CA) model was utilized to study the effects of Marangoni convection on the solidification microstructure. The results reveal that the induced convection is strong enough to bend dendrites from preferential crystallographic direction and can affect the dendrite growth rate, which can affect the subsequent mechanical and physical properties.
3:30 PM Break
3:50 PM Cancelled
Breakouts During Casting (The Big Casting Monster): Magdy Feshar1; Mohmaed Abomossaes1; 1EZZ Dekhila Steel company
Steel industry has many challenges for producing steel with higher quality, low cost by decreasing plant stoppage for any trouble, SO EZZ steel Group slogan, high productivity with high quality accompanied by low cost, so to achieve the highest productivity and reach our targets, the plant stoppage should be decreased, the most and monster of any casting process is the breakout under the mould during casting as it causes plant stoppage from 1 hour to 9 hours so analysis, controlling and review the crews’ performance are considered to be some important things to control the breakout numbers,Many actions were taken as Camera system was installed to review crew’s performance, process parameters enhancement and many job instructions were issued to decrease the breakout numbers by half (from 42 in 2015 to only 2 breakouts per year in the 1st half of 2019).
4:10 PM
Deformation Induced Crack Growth in Semi-solid Die Cast Aluminum Alloys: Shishira Bhagavath1; Zhixuan Gong2; Sara Nonni2; Tim Wigger2; Saurabh Shah2; Sebastian Marussi2; Neeraj Srivastava1; Shyamprasad Karagadde1; Peter Lee2; 1Indian Institute of Technology Bombay, India; 2University College London
High Pressure die casting (HPDC) is a process used for the rapid production of aluminum and magnesium alloy castings with excellent surface finish and shape conformation. Due to the extreme cooling, flow and pressure conditions prevailing during the process, the semi-sold mushy zone in HPDC is subjected to a state of complex stress. In this study, semi-solid deformation experiment of die cast Aluminum alloys were conducted to replicate the process stress conditions. The deformed samples were characterized using the X-ray radiography and tomography techniques to quantify the volume fraction, number density, and 3D distribution of the porosity and silicon particles. The results revealed the agglomeration of silicon particles in the deformed sample and subsequent growth of cracks around it. To understand this further, the role of secondary particles on mushy zone permeability and feeding was investigated. The results will help in developing better predictive models for porosity prediction in HPDC.