Defects and Properties of Cast Metals: Properties II
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 8:30 AM
February 25, 2020
Room: 17B
Location: San Diego Convention Ctr
Session Chair: Peter Lee, University College London; Mark Easton, RMIT University
8:30 AM Cancelled
Refinement of Coarse Intermetallics in Hypereuectic Al-Si Alloys with High Fe, Mn Contents: Carmelo Todaro1; Mark Easton1; David StJohn2; Ma Qian1; 1RMIT University; 2University of Queensland
Hypereutectic Al-Si with Fe and Mn contents up to 4wt% have been treated ultrasonically and with laser re-melting. Ultrasonic treatment led to a more homogeneous distribution of the phases, a reduction in the porosity and substantial microstructural refinement. The combination of ultrasonic treatment and Mn addition provided additional microstructural control by modifying the morphology of the intermetallics from platelet-like to polyhedral. Laser surface remelting of the cast alloy replaced pre-eutectic intermetallic platelets (length >100 μm) with a strong three‑dimensional interconnected network of co‑eutectic intermetallics (length ~2 μm), causing the tensile properties of the alloy to increase dramatically.
9:00 AM Invited
Modification of Al-Si Alloys with Rare Earth Elements: Prakash Srirangam1; 1Wmg, University of Warwick
Aluminium-Silicon (Al-Si) alloys are widely used in the automotive, aerospace and casting industries due to their excellent mechanical and performance properties. Modifying elements such as strontium or rare earth elements (RE) such as yttrium and cerium are added to these alloys to transform the plate-like silicon morphology to fibrous morphology. In this study, Al-Si alloys were modified with strontium, yttrium and cerium and these cast alloys were characterised by using SEM, TEM and 3D X-ray Computed Tomography (XCT). Results show that the addition of strontium resulted in an increase in porosity as compared to yttrium and cerium additions in Al-Si alloys. It was observed that the addition of strontium fully modified the eutectic silicon, while yttrium and cerium only partially modified the eutectic silicon phase in these alloys. These results along with the quantified information on porosity and intermetallic particles formation in modified Al-Si alloys will be presented.
9:30 AM
The Influence of Ultrasound on the Microstructure Formation During the Solidification of A356 Ingots Processed via a 2-Zone Induction Melting Furnace: Aqi Dong1; Laurentiu Nastac1; 1University of Alabama
To study the formation of the microstructure under the influence of ultrasound, a 2-zone furnace and an ultrasound system were used. The 2-zone furnace is an induction furnace with two separate coils (a top coil and a bottom coil). By controlling both the top and bottom coil output power independently, the furnace can create various temperature gradients including a mushy zone and cooling rates in different regions of the graphite crucible. A water-cooled chill block was applied at the bottom of the crucible. The ultrasound probe was inserted at the top of the crucible. The top of the crucible was also thermally insulated. A numerical model was developed to predict the temperature gradients and mushy zone evolution in the crucible. The effects of ultrasound on the microstructure formation in A356 alloy was studied. Cooling curve analysis was performed at various locations in the crucible.
9:50 AM
Ti Fading Effect in Primer and Seconder A356 Alloys and Melt Quality: Ozen Gursoy1; Eray Erzi2; Derya Dispinar2; 1ITU; 2Istanbul University
Ti is the most preferred element as a grain refiner but grain refinement mechanism and performance are matter of debate because of fading effect. Due to the density difference, Ti compounds that will form nucleation centre collapse to the bottom of the crucible and lose the efficiency. In this study, correlation between Ti-grain refinement process and bifilm precipitation by Ti compounds was investigated. Primer and seconder A356 alloys were used. After the addition of grain refiner, melt quality chance was monitored collecting RPT sample every 8 minutes. To determine the mechanical properties, tensile samples were cast into the die and sand moulds at same period. It was observed that melt quality increased in time. Differences of mechanical properties were noteworthy.
10:10 AM Break
10:30 AM
Tensile Properties Limits of A356 Alloy by Porosity: Ozkan Kesen1; Selim Temel1; Okan Aydin1; Furkan Tezer1; Ozen Gursoy1; Derya Dispinar2; 1ITU; 2Istanbul University
Porosity has great importance in aluminium alloys and turbulence is one of the main causes of porosity. Turbulence caused by the movement of liquid metal is the main cause of bifilm. One of the parameters affecting amount, shape and size of porosity is the oxide type and size that is incorporated into the liquid melt. For this reason, in this study, porosity-dependent tensile properties of A356 alloy were investigated. Different size, shape and number of pores were drawn in tensile test bars and Ansys was used to find the fracture stress. A model was evaluated and a map was drawn to estimate the life of cast part. CT Scan was used to validate the model.
10:50 AM Cancelled
Effect of Zr Additions on Microstructure and Mechanical Properties of Gravity Die Cast AlSi7Mg0.4 Alloys: Yunxiang Zhang1; Hai-Dong Zhao1; Changhai Li2; Lin Zhu2; 1South China University of Technology; 2CITIC Dicastal Co.,Ltd.
AlSi7Mg0.4 alloys are one of the most applied aluminum alloys for various casting processes. In this study, 0.06% and 0.14% Zr were added into AlSi7Mg0.4 alloys fabricated with gravity die casting method. The microstructure analysis of the as-cast alloys shows that (Al, Si)3(Zr, Ti) and π-Fe with Zr phases formed. Compared with the AlSi7Mg0.4 alloys without Zr, the alloys with Zr have smaller secondary dendrite arm spacing (SDAS) and their dendrites show preferred growth orientation. After T6 heat treatment, Mg and Si in the eutectics were dissolved into α-Al matrix, and Mg and Zr in the Fe-rich intermetallics diffused into the matrix, which decreased the intermetallics sizes. Due to the precipitation strengthen in the aging and the decreased SDAS, the tensile strength and elongation of the alloys with Zr are 332MPa and 8.7%, respectively, whereas those of the AlSi7Mg0.4 alloys without Zr are 302MPa and 4.6%.