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Heat Treatment

In order to improve considerably the mechanical properties of the alloy, and in order to eliminate the eventual residual internal tensions, the casting are submitted to heat treatments of ageing and solution heat treatment

Heat treatment basic phases are three:

- The heating phase

- The permanence phase

- The cooling phase

Heat treatment basic phases are three: the heating phase, the permanence phase and the cooling phase. The internal temperature of the furnace, during the  first phase, has to increase very slowly, in order to avoid different temperature (and the consequent different expansion) between inner and outer sides of the casting, since they should cause tensions and cracks.

During the permanence phase, its temperature and its length are of great importance for the results of the heat treatment.
They depend on the dimensions of the casting, and on the required mechanical properties.

The cooling of magnesium castings has to be effected with "forced air" in order to quicken the speed of this phase; in base of it different mechanical properties and structure are given to the casting: fastener is the cooling phase higher are the obtained mechanical properties.

MECHANICAL PROPERTIES AZ91

T4= 16/24 hours at 400/420°C, cooling

T6= 16/24 hours at 400/420°C, cooling, then 8/16 hours at 180/210°C

F= Raw casting

T4= Casting after T4 heat treatment

T6= Casting after T6 heat treatment