Journal
JOURNAL OF CENTRAL SOUTH UNIVERSITY
Volume 28, Issue 9, Pages 2636-2646Publisher
JOURNAL OF CENTRAL SOUTH UNIV
DOI: 10.1007/s11771-021-4798-3
Keywords
Al-3; 0Mg-0; 5Si alloy; Li addition; microstructure; ageing behavior; mechanical properties; dynamic elasticity modulus
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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.
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.
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