Aluminum and aluminum alloys-heat treatment of aluminum and aluminum alloys(2)

Quenching

If you want to get the best results, this is a critical operation that must be precisely limited. The purpose of quenching is to ensure that the dissolved components are kept at room temperature in the solution.

The quenching speed is important, and the results may be affected by excessive delay in transferring the workpiece to quenching. The latitude of the delay depends on the cross section. For objects with a thickness ranging from 0.4mm to 12.7mm, the range is from 5 to 15 seconds. In general, for most alloys, the very rapid precipitation of components starts at about 450°C and the work must not be allowed to fall below this temperature before quenching.

Another factor to consider when quenching is the work load and the ability of the quenching agent to extract heat at a sufficient rate to obtain the desired result.

The usual quenching medium is water at room temperature. In some cases, slow quenching is desirable because it improves the stress corrosion cracking resistance of certain copper-free Al-Zn-Mg alloys.

Parts with complex shapes such as forgings, castings, impact extrusions and components produced from sheet metal can be quenched at a slower quenching rate to improve distortion characteristics.

Therefore, in some cases, compromise must be considered to achieve property balance. Quenching agents for slower quenching applications include water heated to 65-80°C, boiling water, an aqueous solution of polyalkylene glycol or forced air blowing.