Effect of Li content on ageing precipitation behavior of Al-Mg-Si alloy

Abstract

The effect of Li content on the ageing precipitation behavior of Al-3.0Mg-0.6Si alloy was investigated by transmission electron microscopy. The evolution and distribution of the precipitation phases in alloys with different Li contents during the artificial ageing at 170 ℃ were analyzed. The results show that the addition of Li changes the ageing precipitation behavior of Al-3.0Mg-0.6Si alloy.In the alloy with 2.15%(mass fraction) Li addition, the spherical δ'-Al3Li phases are formed first in grain interiors, while the needle-shaped β″-Mg2Si phases gradually precipitate at the later ageing stage. After ageing for 192 h, there are obviously dual phase precipitation of spherical δ' phase and needle-shaped β″ phase formed.However, β″ phase precipitation is not found in the alloy with 3.12%Li addition during the observed ageing stage. In addition, there are no precipitation phases at the grain boundaries of the Li-containing alloys, and the precipitate-free zones (δ'-PFZs) and δ' phase are found nearby the grain boundaries. After ageing for 100 h, the alloy with 2.15%Li addition precipitates needle-shaped β″ phase in the δ'-PFZs regions. Both the half width size and growth rate of the δ'-PFZs in the alloy with 2.15%Li addition are greater than that of 2.68%,3.12%Li alloys.

Keywords

• al-li alloy
• al-mg-si alloy
• precipitation phase
• precipitate-free zone
• microstructure