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Modeling Microstructure During Heat Treatment

Simulating local microstructure could provide a tool for optimizing part geometry and casting operations to achieve desired mechanical properties at desired locations. A MODERN CASTING STAFF REPORT


luminum castings are often specified for T6/T7 heat treat- ment to improve their mechanical properties and reduce internal

residual stresses. However, this heat treatment has shown to improve the properties only in specific alumi- num alloys that precipitate sufficient amounts of copper and magnesium- rich phases at the end of solidification. Local cooling conditions, feeding conditions and gas content of the cast- ing define its properties. While casting designers and procur-

ers primarily care about the residual stress condition of the final, machined casting and its properties prior to assem- bly, those properties change throughout the manufacturing 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. Cop- per/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 and Christof Heisser, Magma Foundry Technologies, Schaumburg, Ill., recently wrote a paper, “Modeling of Micro- structure and Mechanical Properties of Aluminum Alloys During the Casting and Heat Treatment Process,” based on

34 | MODERN CASTING September 2012

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 treat- ment, quenching and aging. Te changes within the

microstructure are solid phase transi- tions and primarily diffusion-driven

ADDING IT ALL UP Breaking down the industry’s latest research papers is as easy as 1-2-3.

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.


2 3

Background—The strength profile for AlSiMg alloys with magnesium concentrations show a steep increase in yield strength through the precipitation hardening, a subsequent plateau with the final peak value, followed by a slow decrease in yield strength due to over aging, accord- ing to actual measurements and software simulations. Procedure—Researchers attempt to predict local microstructure and its affect on mechanical properties for a cylinder head casting using advancements in modeling techniques and abilities Results and Conclusions—Overall, the researchers believe the results of the cylinder head tests show the as-cast microstructure, including phase and porosity distribution and mechanical properties after heat treatment, can be predicted.

the solidification process, at which point the phases contain the bulk of the magnesium or copper, depending on the initial melting composition. Te size and distribution of these

processes. Te 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. Tis leads to the precipi- tating hardening effect, which results in better mechanical properties. Solution heat treatment dissolves Cu phases and creates

a condition where empty spots are present within the crystal structure as much as possible. Te higher the

the Mg2Si or Al2

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