Defects and Properties of Cast Metals: Defects I - Molten Metal and Inclusions
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 8:30 AM
February 27, 2017
Room: 23A
Location: San Diego Convention Ctr

Session Chair: Mark Jolly, Cranfield University; Matthew Krane, Purdue University

8:30 AM Introductory Comments

8:35 AM  Invited
Uncertainty Quantification in Modeling an Industrial High Pressure Die Casting Process: Jiahong Fu1; John Coleman2; Amy Marconnet1; Matthew Krane2; 1School of Mechanical Engineering, Purdue University; 2School of Materials Engineering, Purdue Center for Metal Casting Research, Purdue University
    Commercial codes find industrial application in the simulation of solidification behavior and defect formation in High Pressure Die Casting (HPDC). Reliability of simulation results depends on the users’ confidence in the similarity of model setting to the real physical phenomena in casting process, and the uncertainty in the material properties. In this work, a commercial code is used to simulate the HPDC process of a transmission plate made of aluminum alloy A380 with thermophysical properties represented by experimentally derived probability distribution functions. The impact of property input uncertainties on specific outputs of interest are examined. Sensitivities and output probability density functions are produced for fraction of the casting still liquid at different times and for the final porosity of casting. These results allow better calculation of margins of production safety and estimation of reliability of HPDC process.

8:55 AM  Invited
Casting Defects Prediction and Control in GE’s Brilliant Factory: Lang Yuan1; Ade Makinde1; Huijuan Dai1; Aymeric Moinet1; Matteo Bellucci1; 1GE Global Research
    GE’s Brilliant Factory is bridging the physical and the digital worlds to create a new breed of manufacturing. The creation of Digital Twin and Digital Thread for casting processes will lead to seamless and real-time simulation capability, from initial CAD design to final performance evaluation. This will significantly advance the high-quality casting parts production with short lead time and low cost. Casting defect prediction and control is one of the key requirements in the establishment of digital twin, allowing casting foundries to open up the design space, accelerate the process development, optimization, and therefore its qualification. A breath of digital techniques has been applied to optimize both the part/ gating system design and casting conditions, to control multi-scale defects, e.g. porosity, cracking and segregation for desired performance. Cases will be discussed, demonstrating how to leverage model-based models, physics-based models and advanced data analysis to control defects in casting processes.

9:15 AM  
Effect of Solidification Conditions on the Formation of Sludge in High Pressure Die Casting of Aluminum Alloy AA383: Tao Liu1; Laurentiu Nastac1; Luke Brewer1; Vishweshwar Arvikar2; Ilya Levin2; 1The University of Alabama; 2Nemark Alabama
    This presentation will examine the effects of solidification conditions (thermal gradient and cooling rate) on the formation of sludge phases (Fe-rich intermetallics) in a modified AA383 Al-Si-Cu alloy. The sludge constituent plays an important role in the mechanical properties of high pressure die cast components. Modified AA383 castings were created using a 3200T Buhler high pressure die cast machine. Samples with different cooling rates were selected from various regions of a much larger casting. The amount and type of sludge defects were determined by optical, SEM and TEM methods. Initial results suggest that higher cooling rates produced microstructures with finer feature sizes and a smaller fraction of sludge. These results are combined with microscopic analyses of modifiers, such as Sr, on the formation of sludge. In addition, thermal analysis experiments are being performed to characterize the sludge formation process and the impact of cooling rate on this process.

9:35 AM  
Wetting Characteristics of CMSX-4 on Various Ceramic Substrates for Use in Investment Casting of Turbine Blades: Logan Kroneman1; Matthew Krane1; Kevin Trumble1; 1Purdue University
    When attempting to cast fine features, sharp corners can often become rounded as a result of the inability for the liquid metal to fully fill the mold. This inability to fill can be related to the wetting characteristics of the system, which are influenced by the composition and roughness of the mold wall. By better understanding how the mold surface affects the contact angle as a function of time, a mold system can be designed to improve the precision of the as-cast shape. Sessile drop experiments were performed with CMSX-4 and a series of ceramic substrates of differing composition and surface roughness in order to measure the contact angle as a function of time. The substrates were examined for interactions with the liquid metal, such as the formation of reaction products. The results of these experiments can better inform decisions regarding investment casting mold systems in order to improve castings.

9:55 AM Break

10:15 AM  Invited
Modeling of Air Entrainment and Inclusions in Steel Casting: Seyyed Hojjat Majidi1; Christoph Beckermann1; 1University of Iowa
    Non-metallic inclusions represent one of the most prevalent and severe defects present in steel castings. The most common forms of inclusions are those resulting from reoxidation of the steel during pouring. A computational model is developed to predict the formation of reoxidation inclusions during pouring of steel castings, the subsequent advection and buoyant movement of the inclusions, and their final size and location in the solidified casting. Air entrainment during filling is modeled using a novel approach that takes into account the turbulent motion of the melt at the free surfaces. Experiments are conducted to better understand the physical mechanisms leading to reoxidation during mold filling. The predictions compare favorably to the experimental data.

10:35 AM  
Modeling of Mechanical Properties of Al Oxide Films Using Molecular Dynamics: Jialin Liu1; Qigui Wang2; Yue Qi1; 1Michigan State University; 2General Motors Company
    Alumina films form instantaneously when fresh liquid aluminum is exposed to air. During casting, alumina thin-film (~2nm) can be easily entrained into final product due to turbulence and folding mechanism. The buried alumina films play significant roles in porosity and microstructure formation during solidification and thus the final mechanical performance of cast products. This paper reports the formation and mechanical properties of alumina using molecular dynamics with reactive force field. The formation history was mimicked by simulating oxidizing liquid aluminum at elevated temperature then cooling to room temperature. The mechanical properties of thin-film and bi-film with different formation history were compared. The results showed nanoscale alumina thin-film behaves ductile during deformation. The flow stress of thin-film is proportional inversely to thickness due to surface Al-O bond realignment. The Al/O-ratio affects the bi-film formation at metal/oxides interface. This work provides insights into the actual impact of alumina bi-film on casting products.

10:55 AM  
Porosity Change of A356 by Excess Sr Addition: Baturalp Atakav1; Ozen Gursoy1; Eray Erzi1; Derya Dispinar1; 1Istanbul University
    The most widely used aluminium alloys are 3xx series that contain Si as the major alloying element. Silicon is not dissolved in aluminium and remains as coarse crystalline. Approximately 100 to 200 ppm strontium is added in order to alter this thick structure to finer fibrous morphology. This modification causes mechanical properties to be increased. In addition, eutectic temperature is decreased which causes improved fluidity. Therefore, there are several studies on Sr modification of Al-Si alloys. However, there is a long going debate in literature as to whether Sr addition increased porosity or not. In this work, excess amount of Sr (1 wt%) was added to A356 alloy and bifilm index of the melt was measured after prolonged holding time. The tests were repeated three times and it was found that bifilm index and number of bifilms were decreased significantly after 1 hour of holding due to healing of bifilms.

11:15 AM  
Rejection Rate-melt Quality Relationship in High Pressure Die Casting of Al-Si Alloys: Halil Kalkan1; Omer Vardar1; Eray Erzi1; Derya Dispinar1; 1Istanbul University
    Controlling the quality of liquid metal is the most important parameter to decrease rejection rate in high pressure die casting of aluminum alloys. In this work, 3 different cases were investigated. In each tests, melt quality was measured by reduced pressure test and bifilm index was recorded. In first case, blister formation after heat treatment was correlated with melt quality. In second case, decrease in hard spots and improved surface finish was found when AlTiB was not used. In third case, PCD (polycrystalline diamond) tool life was significantly improved when provider with better charge quality was used. In each cases, a direct correlation between melt quality (bifilm index) and the rejection rate was observed.

11:35 AM  
Quantification of A356 Melt Quality Change after Several Recycling: Abdullah Sasmaz1; Ozen Gursoy1; Eray Erzi1; Derya Dispinar1; 1Istanbul University
    It is well known that aluminium is recyclable and it saves significant amount of energy compare to primary production of aluminium. However, there is a common belief that secondary aluminium quality is bad. In this work, the change in bifilm index and bifilm number of recycled A356 have been investigated. Reduced pressure test was used and samples were solidified under 100 mbar in a sand mould in order to slowly the cool the melt and unravel bifilms. In addition, various ratios of Ti was added to the alloy as 0.1 and 1 wt% by Al5Ti1B. The alloy was melted five consecutive times. It was found that the melt with higher Ti had significantly improved melt quality after each recycling due to sedimentation of bifilms by titanium.

11:55 AM  
Modification Efficiency of Sr in A360 and A413 and Its Relation with Melt Quality: İnal Kaan Duygun1; Ozen Gursoy1; Eray Erzi1; Derya Dispinar1; 1Istanbul University
    Strontium modification of Al-Si alloys has many advantages for the casting parts. Particularly, mechanical properties are increased and castability of the alloy is improved. However, Sr has high affinity to oxygen and it may form SrO.Al2O3 spinel oxides on the surface of the melt depending on the holding time of the liquid. Thus, Sr quantity in the melt can decrease by time. In this work, this phenomenon was investigated in two different alloys: A360 and A413. The melt was held at 700 and 750oC for 4 and 17 hours. Metallographic examination was carried out for the Sr fading effect measurement. In addition, melt quality change was recorded by means of bifilm index change. It was found that bifilm index was decreased (quality was increased) and modification was hindered.