Reaching optimum properties: Heat and surface treatment in the die casting industry
Christopher Boss
Leiter EUROGUSS & Geschäftsführer bei MedtecLIVE GmbH | Neue Geschäftsentwicklung, Marketingkommunikation, Projektplanung | Veranstaltungsprofi mit >15 Jahren Erfahrung
Die-casting processes enable the cost-effective production of narrowly tolerated parts that have many beneficial characteristics. In certain cases, it is possible to optimize the mechanical properties even further by means of heat and surface treatment procedures.
Die-cast parts which are manufactured in the conventional manner are considered to be not heat-treatable, or only with difficulty. The reason is that gases are dissolved or trapped in the molten metal. When such cast parts are heated up to higher temperatures which are necessary for heat treatment operations, these gases expand and form bubbles with a negative impact on the mechanical strength and the dimensional accuracy of the parts. A way out is offered by procedures such as vacuum die-casting [1] and laminar die-casting.
Precipitation hardening
Parts which are made of heat-treatable alloys and produced with the mentioned procedures can be heat-treated. It is characteristic for the vacuum die-casting procedure that all areas of a casting machine which are reached by the melt are evacuated. Also the gases which arise when the melt flows in are continuously exhausted by a vacuum. When using the laminar die-casting process, on the other hand, a relatively low mould filling speed prevents that gases are trapped. The cast parts are annealed according to a time-temperature-profile which depends on the alloy and the dimensions. In this way, a homogeneous solid solution is generated in the parts. After a certain annealing time, the parts are quenched in water and in some cases re-annealed once more. This procedure is called T6 heat treatment [2 and 3]. After the first annealing process, the solution annealing, the solid solution is supersaturated with alloying atoms. A longer ageing of the parts at room temperature or at elevated temperatures has the effect that the surplus alloying atoms diffuse out from the solid solution, accumulate in certain boundary zones and form intermetallic compounds. During this process called precipitation hardening, the hardness and the mechanical strength of the microstructure and therefore also of the cast parts increase [4].
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Engineering Head/ME/NPD/Design - Ex Honda/ Ex Maruti Suzuki/ Ex Motherson
7yVery true Christopher Boss.... and thanks for posting this article. Yes we are producing some parts with 50 microns accuracy as cast condition but those parts does not require any heat treatment and complete credit goes to the Die designing.