Influence of Natural Aging and Ramping Before Artificial Aging on the Microstructure of Two 6xxx Alloys

In this study the effect of a ramp up to artificial aging (AA) temperature in combination with natural aging (NA) was analysed for two different industrial aluminum alloys. The peak aged conditions of the alloys were investigated. NA prior to AA reduces the strength as compared with directly aged regardless of ramping. The hardness up to peak is very similar for conditions with and without the ramp if NA is performed, but for the Cu rich alloy a clear increase in peak hardness could be measured when ramped from the SSSS. Investigations by (scanning) transmission electron microscopy found longer precipitates when ramped from a SSSS and an increased precipitate number density when ramped after NA. Less hybrid-type precipitates could be found for all ramped conditions. Atom probe tomography measurements showed that more solute is left in the matrix between the precipitates when ramped