Aging behavior and precipitate characterization of Zn-rich Al–Zn–Mg–Cu alloys with various Mg and Cu contents

Four Zn-rich Al–Zn–Mg–Cu alloys with different Mg and Cu contents were fabricated by spray deposition. The effects of Mg and Cu contents on the aging behaviors of the whole precipitation process of the alloys were systematically investigated. The results show that the primary precipitates in the under-aged and peak-aged alloys are GPII and η′ phases; no GPI zones were observed. During aging, the dissolution driving force of the precipitates increases with increasing Mg content; therefore, the volume fraction of precipitates in the grain interior and the area fraction of precipitates at the grain boundary increase obviously, which contributes to a considerable improvement in yield strength and decrease in plasticity of the high Mg content alloys. Cu content has no apparent effect on the size and volume fraction of precipitates. However, a higher Cu content can effectively prevent coarsening and transformation of precipitates, which is beneficial to maintain the peak aging state of the alloys. This research provides a basis for the composition optimization of the rapid-solidified highly alloying Al–Zn–Mg–Cu alloys.