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

Li元素对Al-3.0Mg-0.5Si挤压合金力学性能和时效析出行为的影响

The effect of Li(2.0 wt%)addition on mechanical properties and ageing precipitation behavior of Al-3.0 Mg 0.5 Si 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,andδ′-Al_(3)Li phase becomes the main precipitates.Besides,β′′-Mg_(2)Si andδ′-Al_(3)Li dual phases precipitation can be visibly observed at 170℃ ageing for 100 h,although the quantity ofδ′-Al_(3)Li phase is more thanβ′′-Mg_(2)Si 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.

本文对比研究了添加2.0 wt%Li元素与不添加Li元素的Al-3.0Mg-0.5Si挤压合金的室温拉伸性能、动态弹性模量和时效析出行为。结果表明,添加Li元素在降低合金密度的同时,还提高了合金的强度和弹性模量,但也导致合金的伸长率大幅度减小,断裂机制从韧性断裂转变为沿晶断裂。微观组织观察显示,Li元素的添加改变了合金的时效析出行为,δ'-Al_(3)Li相成为主要析出强化相。含Li合金在170℃时效100 h后,有明显的球状δ'-Al_(3)Li相和针状β''-Mg_(2)Si相双相析出现象。此外,含Li合金过时效状态下的无沉淀析出带宽度更大,对合金的塑性产生不利影响,造成伸长率下降。