Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

Mechanical properties of B206 aluminium alloys with additions of iron and silicon were studied to investigate the combined effect of these additions on tensile strengths and ductility. Properties are highly influenced by the iron to silicon ratio and the nominal concentration of the single elements. The best properties were obtained with both a ratio close to one and low concentrations of iron and silicon. Present experimental results show that it is possible to multiply by two or three the present limit of 0·1 wt-%Fe in these alloys at natural aging (T4) and still obtain the minimum of 7% elongation required by the automotive industry. At artificial aging (T7), it will be very difficult however to reach the 7% elongation with ~0·2 wt-%Fe and 0·2 wt-%Si, while this seems impossible with ~0·3 wt-%Fe and 0·3 wt-%Si. It was found that macrosegregation of Cu in the gage section of the ASTM B108 test bars is responsible for an enrichment of 0·8-0·9 wt-%of this element in the test zone. This has produced microstructures saturated in Cu with little Al 2Cu phase remaining after the solution heat treatment. Owing to the low amount of this phase and the round shape of the particles, the remaining Al 2Cu phase did not have a significant impact on the ductility. One benefit of working with a Cu saturated microstructure is that one can estimate the true temperature of the solution heat treatment by conducting a post-analysis of Cu content in the dendrites. This should be helpful to reduce the variability in properties and to improve the temperature distribution in heat treating furnaces.