Effect of Li addition on mechanical properties and ageing precipitation behavior of extruded Al-3.0Mg-0.5Si alloy

The effect of Li (2.0 wt%) addition on mechanical properties and ageing precipitation behavior of Al-3.0Mg-0.5Si was investigated by tensile test, dynamic elasticity modulus test, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images. The results show that the tensile strength of the Li-containing alloy can be significantly improved; however, the ductility is sharply decreased and the fracture mechanism changes from ductile fracture to intergranular fracture. The elasticity modulus of the Li-containing alloy increases by 11.6% compared with the base alloy. The microstructure observation shows that the Li addition can absolutely change the precipitation behavior of the base alloy, and delta '-Al3Li phase becomes the main precipitates. Besides, beta ''-Mg2Si and delta '-Al3Li dual phases precipitation can be visibly observed at 170 degrees C ageing for 100 h, although the quantity of delta '-Al3Li phase is more than beta ''-Mg2Si phase. The width of the precipitate-free zone (PFZ) of the Li-containing alloy is much wider at the over-ageing state than the base alloy, which has a negative impact on the ductile and results in the decrease of elongation.

Automated summary

The addition of Li significantly improves the tensile strength and elasticity modulus of the alloy, but decreases ductility and changes the fracture mechanism; Li also alters the precipitation behavior of the alloy, with delta'-Al3Li becoming the main precipitates.