Electron microscopy studies of the age-hardening behaviors in 6005A alloy and microstructural characterizations of precipitates

High-resolution electron microscopy was used to research the age-hardening behaviors in 6005A alloy and the microstructural characterizations of precipitates. It was found that β″, β′ and Q′ precipitates had 12 orientation variants, respectively, the smaller size and a high-density β′′ precipitates existed in alloy for a long time, which played a very important role in controlling an anti-overaged softening behavior in 6005A alloy. Further, by the crystallographic interface and morphology analysis, a main reason was that a 2-dimensions coherency strain-field not only had the high-density β′′ precipitates become the biggest obstacle of dislocations movement, but also made them transform into β′ and Q′ precipitates with more difficulty. Moreover, it was also found that β′ and Q′ precipitates had weaker relatively strain-fields, the larger size and a lower density, which were largely associated with the reduction in hardness that occurred upon overaging. Further, the strengthening of precipitates on alloys could be summarized as: β″ > Q′ > β′. Based on the structural information, the quantitative Moiré fringes analytical technique was also used to verify the lattice parameters and orientation of precipitates.

► TEM and HREM are used to elucidate an anti overaged softening behavior in Al–0.65Mg–0.73Si–0.13Cu alloy. ► The β″ precipitate not only has a 2-dimensions coherency strain-field, but also has the smaller size and a high density. ► The strengthening of three main precipitates on alloy can be summarized as: β″ > Q′ > β′. ► The β″, β′ and Q′ precipitates have 12 orientation variants with Al matrix, respectively. ► Moiré fringes are used to verify the lattice parameters and orientation variants of precipitates.