Dry and clean age hardening of aluminium alloys by high-pressure gas quenching

When precipitation hardenable aluminium parts are water quenched, distortion occurs, because of thermal stresses. Thereby a costly reworking is necessary. For this reason polymer quenchants were. often used to reduce distortion, with the disadvantage, that the quenched parts have to be cleaned after quenching. Gas quenching may decrease distortion, because of the better temperature uniformity during quenching. Furthermore, cleaning of the quenched parts can be avoided, because of the dry process. For this purpose a heat treating process was evaluated, which includes a high-pressure gas quenching step. Gas quenching was applied to different aluminium alloys (2024, 6013, 7075 and A357.0). Tensile tests have been carried out to determine the mechanical proper-ties after solution annealing, gas quenching and aging. Besides high-pressure gas quenching, the alloy 2024 was quenched at ambient pressure in a gas nozzle field. The high velocity at the gas outlet will lead to an accelerated cooling of the aluminium alloy in this case. Aluminium castings and forgings can be classified as an interesting field of application of these quenching methods, because of their near-net shape before the heat treatment. Cost savings would be possible, because of the reduced distortion and therefore less reworking after the precipitation hardening.