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Modeling Microstructure During Heat Treatment

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Simulating local microstructure could provide a tool for optimizing part geometry for desired mechanical properties at desired locations.

luminum castings are often specifi ed for T6/ T7 heat treatment to improve their mechanical properties and reduce internal residual stresses. However, this heat treatment has shown to improve the properties only in specifi c alumi- num alloys that precipitate suffi cient amounts of copper and magnesium-rich phases at the end of solidifi cation. Local cooling conditions, feeding conditions and gas content of the casting defi ne its properties. While casting designers and procurers pri-

marily care about the residual stress condition of the fi nal, machined casting and its properties prior to assembly, those properties change throughout the manu- facturing process. During the solution treatment process step, near the solidus temperature, copper and magnesium-rich phases derived from the casting process go into solution again. Subsequent quenching should be controlled so it does not create high residual stresses and to assure copper and magnesium stay in solution. Copper/magnesium is needed in the aging process to modify the microstructure in a controlled way through the precipitation of intermetallic phases. Advancements in casting process modeling include the ability to simulate local microstructure through casting and heat treatment. Authors Marc Schneider, Magma


Modeling of Microstructure and Mechanical Properties of Aluminum Alloys During the Casting and Heat Treatment Process. Marc Schneider, Magma Giessereitechnologie GmbH, Aachen, Germany, and Christof Heisser, Magma Foundry Technologies Inc., Schaumburg, Ill. Background—The strength profi le for AlSiMg alloys with magnesium concentrations shows a steep increase in yield strength through the precipitation hardening, a subsequent plateau with the fi nal peak value, followed by a slow decrease in yield strength due to over aging, according to actual measurements and software simulations.

Procedure—Researchers attempt to predict local microstructure and its affect on mechanical properties for a cylinder head cast- ing using advancements in modeling techniques and abilities.

Results and Conclusions—Overall, the researchers believe the re- sults of the cylinder head tests show the as-cast microstructure, including phase and porosity distribution and mechanical proper ties after heat treatment, can be predicted. 

Giessereitechnologie GmbH, Aachen, Germany, and Christof Heisser, Magma Foundry Technologies, Schaumburg, Ill., recently wrote a paper, “Modeling of Mi- crostructure and Mechanical Properties of Aluminum Alloys During the Casting and Heat Treatment Process,” based on research conducted to investigate how local microstructure information can be used as input parameters to simulate further process steps, such as lifetime prediction, as well as to determine how to achieve desired mechanical properties within economical boundaries.


Can process simulation, compared with measured data, be used to predict local microstructure through each casting process and the entire heat treatment?


Background A T6/T7 heat treatment

consists of solution treatment, quenching and aging. T e changes within the mi-

the solidifi cation process, at which point the phases contain the bulk of the magnesium or copper, depending on the initial melting composition. T e size and distribution of these

crostructure are solid phase transi- tions and primarily diff usion-driven processes. T e hypoeutectic AlSiMg, AlSiCu and AlSiMgCu alloys create Mg2

Si or Al2 Cu phases at the end of

phases in metalcasting are not optimal for desired mechanical properties, and heat treatment is used to bring the phases into solution again and precipitate them in a desired size and distribution. T is leads to the precipi- tating hardening eff ect, which results


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