The aluminum heat treatment industry has a great variety of products and processes designed to enhance the material’s physical properties. Quenching is a process that involves cooling the workpiece at a rapid rate to increase its hardness.

Quenching with air results in a mostly uniform, but slow, process. The long cooling times affect the workpiece’s hardness. Another popular quenching method is using a water tank, which gives faster cooling rates given the calorific capacity and thermal conductivity of the medium, and thus, better hardness properties.

However, the formation of a vapor layer around the workpiece results in an uneven cooling rate, which produces undesired distortion and a more brittle material. Quenching with a mixture of pressurized air and atomized water combines the cooling times of water-quenching and the uniformity of air-quenching.

An experimental design was set up in Nutec Bickley’s testing lab to obtain the cooling curves for an aluminum workpiece heated to 525°C and then quenched with different media: in a water tank, with air, and with an air-mist mixture.  Table 1 shows the average cooling rates and the time it took for the piece to reach 100°C for each quenching method.

Quench media

Average cooling rate

Time to reach 100°C


-11.46 °C/min

19.88 min

Air-mist (LV)

-12.52 °C/min 12.16 min
Air-mist (HV) -12.51 °C/min

10.73 min

Water tank -12.75 °C/min

1.09 min

Table 1.
 Average cooling rates and times for each quenching method.


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