Defects and Properties of Cast Metals: Defects II & Properties I
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Solidification Committee
Program Organizers: Mark Jolly, Cranfield University; Charles Monroe, University of Alabama; Brian Thomas, Colorado School of Mines; Peter Lee, University of Manchester

Monday 2:00 PM
February 27, 2017
Room: 23A
Location: San Diego Convention Ctr

Session Chair: Steven Cockcroft, University of British Columbia; Andrew Kao, University of Greenwich


2:00 PM Introductory Comments Defects II session

2:05 PM  
Reducing Freckle Formation with External Magnetic Fields: Andrew Kao1; Koulis Pericleous1; 1University of Greenwich
    The formation of freckles during the production of Ni superalloy turbine blades can be detrimental to their performance. Freckles have been shown to form when channels of solute ejecting buoyant plumes become stable during casting. The authors present numerically the use of external magnetic fields for destabilising these channels and so reducing the chance of a defect forming. By turning on and off a DC magnetic field to this system, electromagnetic damping and modification to the thermodynamic interface equilibrium may be able to destabilise these channels. Though the use of a fully coupled numerical model that includes solidification, fluid flow and electromagnetism, this paper investigates the effects the magnetic field will have on plume formation, the underlying microstructure and flow driven by Thermoelectric Magnetohydrodynamics; a secondary phenomenon introduced by the magnetic field.

2:25 PM  
Modelling the Effects of Fluid Flow on Microstructure Evolution at the Component Scale: Matthaios Alexandrakis1; Andrew Kao1; Koulis Pericleous1; 1University of Greenwich
    Predicting the formation of defects and macroscopic material properties of components is very important to modern industry. Many factors affect the formation of defects including fluid flow and the geometry of the component. Through increases in high performance computing (HPC), the ability to predict these features on the component level, but from a microstructural perspective is becoming a reality. This work presents a massively parallel implementation of directional solidification using a Cellular Automata (CA) based method that employs a modified decentred octahedron method. In contrast to phase field methods, the CA method allows the use of larger cell sizes (O10microns), compared to (O1micron) and coupled with massive parallelisation allows for the simulation of billions of computational cells, approaching the scale of small components. The model has been coupled to both an electromagnetic and fluid flow solvers that has allowed the investigation of novel fluid effects such as Thermoelectric Magnetohydrodynamics.

2:45 PM  
Determining Eutectic Grain Size and Casting Defects in an Al-12Si-0.8Cu-0.5Fe-0.9Mg-0.7Ni-0.2Zn Alloy: Jiehua Li1; Bernd Oberdorfer2; Daniel Habe2; Peter Schumacher3; 1University of Leoben; 2Austrian Foundry Research Institute; 3University of Leoben, Austrian Foundry Research Institute
    In this contribution, an Al-12Si-0.8Cu-0.5Fe-0.9Mg-0.7Ni-0.2Zn alloy was investigated. In order to determine eutectic grain sizes, Modified Murakami reagent was used to etch out the eutectic grain boundaries. Furthermore, electron probe microanalyzer (EPMA) was also used to elucidate the distribution of Mg, Fe, Cu, Ni elements, which segregate to eutectic grain boundaries and thereby can be used to determine the eutectic grain size. In order to determine the number, size and distribution of casting defects (pores and inclusions), computed tomography (CT) was used. It was found that casting defects are mostly distributed along the eutectic grain boundaries, strongly indicating the refinement of eutectic grain is of great necessity to optimize the distribution of casting defects and decrease the size of casting defects. This investigation highlights the effect of the refinement of eutectic grain on casting defects and can be further related to the properties, in particular to dynamic fatigue properties.

3:05 PM  
A Modeling and Experimental Investigation on the Formation of Acicular Silicon and Sludge in High Pressure Die Casting of a Modified A383 Alloy: Mikko Kärkkäinen1; Laurentiu Nastac1; Luke Brewer1; Vishweshwar Arvikar2; Ilya Levin2; 1The University of Alabama; 2Nemak
    A numerical model is being developed to predict the formation of sludge (e.g., Fe-rich intermetallics) during high pressure die casting (HPDC) of a modified A383 alloy. The sludge plays a major detrimental role in the mechanical properties, especially the fracture characteristics, of high pressure die cast engine components. The modelling approach consists of integrating a macroscopic model for prediction of fluid flow and solidification conditions in HPDC A383 components with a microscopic solidification structure model. The aim of the integrated model is to accurately predict the evolution of the solidification microstructure including the sludge formation in HPDC A383 components. The model predictions are being compared against experimental measurements (e.g., amount, type and size of sludge defects) in A383 samples extracted from various regions of an HPDC engine block. The validated model can then be applied to determine the effects of different solidification conditions on the formation of sludge.

3:25 PM Break

3:45 PM Introductory Comments Properties I Session

3:50 PM  Invited
Influence of Geometry and Aluminum Content on the Microstructure and Tensile Behavior of HPDC Mg AM Series Alloys: Erin Deda1; John Allison1; 1University of Michigan
    The mechanical properties of high pressure die cast (HPDC) magnesium can be highly variable and dependent on the manufacturing process history and on location within a casting. This investigation is providing experimental input to modeling activities for the development of an ICME capability, to assess and quantify the impact of aluminum content and section thickness on the microstructure and tensile behavior of HPDC Mg AM series (magnesium-aluminum-manganese) alloys. Eight conditions of varying thickness and aluminum content were super vacuum die cast and characterized via quantitative metallography and uniaxial tensile testing. Plates were solution treated and processed by hot isostatic pressing (HIP) to identify the effect of different microstructural features, beta phase and shrinkage porosity, on the mechanical behavior. Models for both yield strength and ductility have been developed to predict the influence of aluminum content and sample thickness.

4:10 PM  
Corrosion Behaviour of V and B Grain Refined A360: Eda Ergun Songul1; Cemre Bas1; Derya Dispinar1; Gökhan Orhan1; 1Istanbul University
    In high pressure die casting of Al-Si alloys, the use of Ti as grain refining has many disadvantages mainly due to fading effect. Alternative grain refiners can be added by using V or B. In this work, Al-10V and Al-3B master alloys were used to achieve different ratios from 0.1 to 1 wt% in A360 alloy. The microstructural characterisation show that irregular and heterogeneous dendritic structure was observed in V addition which resulted in poor mechanical properties, however the corrosion resistance was improved. More reproducible mechanical properties were obtained in B addition however corrosion resistance was lower compare to V addition.

4:30 PM  
Assessment of the Impact of Water-Cooled Chill Technology on Microstructure Length-Scales in an A319 Engine Block Casting: Farzaneh Farhang Mehr1; Steve Cockcroft1; Daan Maijer1; Robert MacKay2; Wade Marquardt3; 1UBC; 2Nemak of Canada Corporation; 3Highland Foundry Ltd.
    To comply with the new Corporate Average Fuel Economy (CAFE) standards, the automotive industry is aiming to reduce weight and increase the power and efficiency of small displacement engines through the application of forced induction technologies. As an example, there are now several 2.0 litre turbocharged engines in production, producing in excess of 240 hp. To meet the need for improved fatigue properties in the engine blocks used in these high-output engines, a new water-cooled chill technology is under exploration at UBC in partnership with General Motors and Nemak. A series of experimental and numerical techniques were used to assess the capability of the new chill to extract heat from an A319 casting in the vicinity of the main bearing bulk head. The results show that this method has the potential to achieve a reduction in secondary dendrite arm spacing thus meeting the new microstructural specifications for these engines.