Gas Quenching during Age Hardening of the Aluminium Casting Alloy Al-7Si-0.3Mg

摘要

For quenching of age hardenable aluminium alloys today predominantly aqueous quenching media are used, which can lead due to the Leidenfrost phenomenon to a non-uniform cooling of the parts and thus to thermal stresses. Particularly at thin-walled or complex shaped parts local plastic deformations can occur by the uneven thermal stresses. In relation to the conventional quenching procedures in aqueous media, gas quenching exhibits a number of technological, ecological and economical advantages. In comparison to liquid quenching media, gas does not change its phase during quenching. Moreover, the cleaning problem of the parts can be avoided. The quenching intensity can be adjusted by the variable parameters gas pressure and gas speed as well as the kind of gas and thus can be adapted to the requirements of the alloy. By the higher uniformity and the better reproducibility, gas quenching offers a high potential to reduce distortion. The goal of these investigations is to clarify, if the cooling rate during gas quenching is sufficient to obtain the specific required strength after age hardening of the alloy Al-7Si-0.3Mg. For this purpose different tests in high-pressure gas quenching facilities, gas nozzle fields and water quenching baths were performed.