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.
|Average cooling rate|
Time to reach 100°C
|-12.52 °C/min||12.16 min|
|Air-mist (HV)||-12.51 °C/min|
|Water tank||-12.75 °C/min|
Table 1. Average cooling rates and times for each quenching method.