Aluminum Alloys, Processing and Characterization: Solidification and Casting
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: Yanjun Li, Norwegian University of Science and Technology
Wednesday 8:30 AM
March 1, 2017
Location: San Diego Convention Ctr
Session Chair: Shouxun Ji, Brunel niversity
8:30 AM Introductory Comments
A Model for α-Al(Mn,Fe)Si Crystals: Christian Simensen1; Are Bjørneklett1; 1SINTEF
A series of large crystals of α-Al(Mn,Fe)Si has been analyzed using microprobe, X-ray diffraction, pychnometer and electrical devices The cubic phase α-Al(Mn,Fe)Si has a density varying from 3520 kg/m3 to 3620 kg/m3. When iron is increased from 1.9 wt% to 20.8 wt%, the content of silicon is reduced from 10.7 wt% to 8.6 wt%. The phase had a low electrical resistivity, 2x10-6 Ωm. Large crystals of α-AlMnSi had a large Seebeck coefficient viz. 42 µV/⁰C. All the crystals were n-semiconductors. A new model for α-AlMnSi has been proposed where Si-atoms are connected in hexagonal rings around 0,0,0 and ½,½,½. The rings are linked by Mn and Si atoms, all covalent bonded. According to this model the ideal α-AlMnSi crystals have 24 Mn-, 18 Si- and 96 Al-atoms in the unit cell. Fe+Al can substitute for Mn + Si atoms in the unit cell. Vacancies can form on Mn-sites.
Casting Characteristics of High Cerium Content Aluminum Alloys: David Weiss1; Orlando Rios2; Zachary Sims2; Scott McCall3; Ryan Ott4; 1Eck Industries, Inc.; 2Oak Ridge National Laboratory; 3Lawrence Livermore National Laboratory; 4The Ames Laboratory
This paper compares the castability of near eutectic aluminum-cerium alloy system to the aluminum-silicon and aluminum-copper systems. The alloys are compared based on die filling capability, feeding characteristics, tolerance to casting defects and tendency to hot tear in both sand cast and permanent mold applications. Differential Scanning Calorimetry (DSC) analysis of the alloys systems is discussed. The castability ranking of the binary systems is as good or better than the aluminum-silicon system with some deterioration as additional alloying elements are added. In alloy systems that use cerium in combination with common aluminum alloying elements such as silicon, magnesium and/or copper, the casting characteristics are generally better than the aluminum-copper system. In general, production systems for melting, de-gassing and other processing of aluminum-silicon or aluminum-copper alloys can be used without modification for conventional casting of aluminum-cerium alloys.
In-situ Observation of Fragmentation of Primary Crystals by Ultrasonic Cavitation in Water: Feng Wang1; Iakovos Tzanakis2; Dmitry Eskin1; Jiawei Mi3; Thomas Connolley4; 1Brunel University London; 2Oxford Brookes University; 3University of Hull; 4Diamond Light Source
Ultrasonic melt processing is a promising technique for microstructural refinement. Several mechanisms were proposed for the observed effects, including cavitation-induced nucleation, activation of substrates and fragmentation. Until now, however, real-time experimental observations are very limited to clarify any of the above mechanisms. We for the first time directly observed the fragmentation of primary crystals formed in aluminum alloys by ultrasonic cavitation. The intermetallics were extracted from real Al alloys and subjected to ultrasonic processing in water with in-situ high-speed filming. The results allowed us to observe the different mechanisms of fragmentation, depending on the properties and morphology of the intermetallics. The collapse of cavitation bubbles in water is less violent than in liquid aluminum due the lower cavitation threshold, viscosity and surface tension. Therefore the fragmentation mechanisms for the intermetallics in water should also be present for the same intermetallics in the more violent cavitation situation in liquid aluminum.
The Enhancement of Mechanical Properties of A356 Alloy Solidified at Lower Cooling Rate via Effectively Grain Refinement: Yijie Zhang1; Shouxun Ji1; Zhongyun Fan1; 1Brunel University
For A356 alloy, solidification with relative lower cooling rate will result in coarse grain size and lower mechanical properties. In this case, Al5Ti1B mater alloy was not the effective one to refine the A356 alloy. In present study, the effective grain refiner for A356 alloy was developed. Experimental results showed that the equiaxed grains were obtained with modified A356 alloy, rather than the dendritic grains of A356 refined by Al5Ti1B master alloy. Compared to the A356 alloy refined by 0.2wt.%Al5Ti1B, the yield strength, ultimate tensile strength and elongation of modified A356 alloy were increased by 4MPa, 30.6MPa, and 4.5% respectively. The value of yield strength, ultimate tensile strength and elongation of modified A356 alloy were 182.3MPa, 278.3MPa and 8.2%. The significant improvement of mechanical properties was ascribed to the effective nucleation of α-Al and the morphology evolution of eutectic Si.
10:15 AM Break
Secondary Aluminum Alloys Processed by Semisolid Process for Automotive Application: Fabrizio D'Errico1; Davide Mattavelli1; 1Politecnico di Milano
OEMs producing safety components require to reduce Fe-contaminant compounds in secondary aluminum alloys, responsible of high brittleness of final microstructure. According to recent advancements, Fe-compounds in recycled aluminum can be controlled trough semisolid process. In this work, investigation about key parameters was conducted, related to the specimen microstructure. Stirring time and solid fraction are key parameters to obtain a globular microstructure. Tensile tests were performed showing promising results (yield strength about 300MPa and ultimate tensile stress about 330MPa were found to be slightly better than standard casting alloys). Semisolid microstructure furthermore allowed breaking of Fe-contaminant compounds, thus producing increase in percentage elongation and toughness, main requirement automotive sector pursues for introducing low-cost and low-environmental impacting secondary aluminum alloys.
Integrated Casting-extrusion of an AA6082 Aluminum Alloy: Shohreh Khorsand1; Yan Huang1; 1Brunel University London
An integrated casting-extrusion is proposed as a novel method for producing profiles of light alloys at low cost and high efficiency. Such a process has multiple advantages, including use of solidification heat, removing the multiple steps in conventional processes and eliminating casting defects. Integrated cast-extrusion experiments have been carried out using an AA6082 aluminum alloy, under fixed casting conditions but variable extrusion temperatures. Experimental results revealed that deformation structure dominated in the as-cast-extruded state with a uniform microstructure and that, upon heat treatment, a uniform distribution of particulate AlFeMnSi and MnSi phases was obtained. EBSD measurements showed that, after T6-5h heat-treatment, a fine grain structure with an average grain size of 30 µm and well developed high angle grain boundaries was successfully achieved. The hardness of the alloy reached to 116HV after 5h aging at 180C, which is comparable to that reported for the same alloy processed by conventional routines.
On Porosity Formation in Al-Si-Cu Cast Alloys: Fawzy Samuel1; Agnes Samuel1; Herbert Doty1; Salvador Valtierra2; 1UQAC; 2Nemak, S.A.
Abstract - The aim of the present work was to investigate the metallurgical parameters controlling porosity formation in Al-Si-Cu alloys, through a study of the microstructural characteristics of directionally solidified 319.2 alloys as a function of iron content, Sr addition (250 ppm), and solidification rate. The iron levels selected varied from 0.12 to 0.8 wt.%, and cover the range of Fe levels found in commercial casting alloys. The use of an end-chilled mold provided different solidification rates along the height of the same casting, with DAS values that varied from ~15 to 85 microns, corresponding to levels of 5, 10, 30, 50 and 100 mm above the chill end. The amount of iron present in the alloy affects the size of the beta-iron Al5FeSi platelets and their distribution, particularly at low solidification rates. Addition of strontium leads to fragmentation of co-eutectic or post-eutectic beta-iron platelets.
Influence of Trace Element Additions on Fe Bearing Intermetallic Solidification of a 6063 Al Alloy: Sundaram Kumar1; Julian Malisano1; Yuri Ito2; Keyna O'Reilly1; 1University of Oxford; 2Tokyo Institute of Technology
There is an on-going effort to control Fe bearing intermetallic formation during solidification in direct chill (DC) casting of dilute Al alloy billets from recycled material sources, as these insoluble Fe intermetallics control the downstream processing conditions and final properties of the processed products. This paper investigates the influence of molybdenum (Mo) and grain refiner combined additions on Fe bearing intermetallic formation during casting of a 6063 Al alloy. In particular, the grain size and intermetallic phase content of the samples have been characterised using various microscopies and X-ray diffractometry. An intermetallic phase extraction technique has been used to facilitate measurement of the three-dimensional morphology and chemistry of the different Fe intermetallics present, with changes rationalized in terms of the effect of trace additions. Both “αc-AlFeSi” and “β-AlFeSi” are observed in all the castings. After the addition of Al-5Ti-1B grain refiner to the base alloy, β-AlFeSi was predominated in the casting. Further addition of Mo to the grain refined alloy promoted αc-AlFeSi in the casting. The possible mechanisms for these effects are discussed.