Modelling of quench sensitivity in automotive 6xxx aluminium alloysWednesday (08.11.2017) 17:00 - 17:20 Part of:
In order to reduce gas consumption as well as CO2 emissions in the automotive industry, one of the key strategies is to reduce weight of the vehicles. This can be done by replacing traditional steel panels with aluminium alloy sheets, typically doors and hoods but also more recently structural parts. 6xxx (Al-Mg-Si) aluminium alloys more specifically have the advantage of being heat-treatable, meaning that they can be delivered in a soft formable temper and hardened during the paint bake cycle of the body-in-white. A critical process step during production of 6xxx sheet is the final solutionizing and quench operations, the objective of which is to keep as much solute as possible in solution within the aluminium matrix in order to keep the full hardening potential of the alloy. The quench factor analysis (QFA) was developed in the ‘70s by Evancho and Staley in order to model the precipitation which may occur during this quenching step.
In this work, a 6xxx alloys with various Mn contents (therefore various dispersoid densities) was used. The QFA model was fitted directly on different non-isothermal quench profiles without the need to perform isothermal treatments. The model successfully predicts the most important precipitates formed during quench based only on the thermal histories and final properties. The model also allows to quantify the effect of Mn on the precipitation during quenching as well as to link the final properties to both composition and process. Metallographic observations (optical, SEM, STEM) were also used to validate the model predictions.