QUENCHING OF ALUMINIUM ALLOYS IN SODIUM SILICATE SOLUTIONS OF VARIOUS SILICATE CONCENTRATIONS

摘要

Precipitation hardening is a common process in heat treatment of automotive components, e.g. chassis parts, cylinder heads andothers. Due to distortions after water quenching subsequent levelling operations or machining is necessary, which causes additional cost. Avoiding or minimizing such distortions is desirable and can be achieved by applying alternative quenching media. The use of aqueous solutions of sodium silicate enables one to adjust the quench severity in between pure water and high concentrated polymer solutions. Since critical cooling velocity is low among the 6xxx alloys in comparison to 2xxx or 7xxx alloys, a smaller cooling rate can be acceptable. Sodium silicate solutions are non-toxic and will cause no environmental hazards. This is an overview about the use of silicate media, the mechanical properties and the hardness of aluminium alloys quenched in sodium silicate solutions of various con- centrations and the possibility of compensating the reduced cooling velocity by modifying the ageing parameters.