Quantifying early-stage precipitation strengthening of Al-Mg-Zn(-Cu) alloy by using particle size distribution

A new generation of aluminum alloys, strengthened by the T-Mg-32(AlZn(Cu))(49) phase, has been created in the last decade based on the 5xxx series Al-Mg alloy, modified with Zn/Cu alloying elements used in 7xxx series alloys. The precipitation strengthening behavior in early stage artificial aging has been an obstacle to the microstructural design and processing control owing to the small size of T-precipitates. The present study aims to quantify the early stage precipitation strengthening behavior, including pre-aging and bake-hardening of the newly developed Al-Mg-Zn alloy with different Cu contents (0 wt% and 0.5 wt%), by particle size distribution via transmission electron microscopy and atom probe tomography. The rapid strengthening response strongly depends on the number density and constitution of Guinier-Preston zone acting as preferential nucleation sites for the precursor of T-phase during the short-term bake-hardening treatment and is significantly increased by the addition of Cu. The coexistence of different types of phases during artificial aging is categorized into clusters, Guinier-Preston zones, and T' precipitates based on microstructural characterization. The yield strengths of the alloy were quantified by adding the strengths of three individual distributions, wherein the precipitation strengthening was evaluated according to the different types of precipitates. These are in reasonable agreement with the reported experimental results. This study sheds light on predicting the precipitation strengthening of alloys using a combination of microstructural observations.

Automated summary

This study quantifies the early stage precipitation strengthening behavior of a newly developed Al-Mg-Zn alloy by particle size distribution. The results show that the rapid strengthening response strongly depends on the number density and constitution of Guinier-Preston zones, and is increased by the addition of Cu. The strength of the alloy is quantified by evaluating different types of precipitates.