Microstructure and corrosion resistance of a duplex structured Mg–7.5Li–3Al–1Zn

This study describes the corrosion resistance of extruded,and extruded with post-processing annealing,Mg–7.5 Li–3 Al–1 Zn alloys.The results demonstrate that extrusion at 350°C with an extrusion speed 0.5 s^(-1) does not lead to the full recrystallization of the alloy,and the material still exhibits a dendritic microstructure.The post-processing annealing triggers the microstructure transformation,and the relative composition of the alloy changes.The ratio ofβ(Li)toα(Mg)in the extruded alloy was 29–71%;after annealing amount ofβ(Li)increased,and the ratio ofβ(Li)toα(Mg)in the annealed alloy was 35–65%.Corrosion testing shows that in 3.5 wt%Na Cl the extruded alloys immediately undergo strong dissolution.As a result of the subsequent annealing,an improvement of corrosion resistance is observed.The higher amount ofβ(Li)in the annealed alloy reduces the area ratio of cathodic to anodic sites of corrosion,and this makes the annealed alloy more resistive under the analyzed conditions.

A comparison of the microstructure-dependent corrosion of dual-structured Mg-Li alloys fabricated by powder consolidation methods:Laser powder bed fusion vs pulse plasma sintering

In this study, powder metallurgy methods were used to fabricate Mg-7.5Li-3Al-Zn alloys from repowdered extruded alloys. Extruded alloys were powdered using ultrasonic atomization, and then laser powder bed fusion(LPBF) and pulse plasma sintering(PPS) were used to consolidate the bulk materials. A comparison of the properties of the fabricated alloys with those of a conventionally extruded one was carried out using methods that characterized the microstructure and corrosion resistance. When compared to their conventionally extruded counterpart, LPBF and PPS materials exhibited refined microstructures with low enrichment in Al Li and coarse Al, Zn, Mn precipitates. The main drawback of the LPBF alloy, printed for the needs of this study, was its porosity, which had a negative effect on its corrosion. The presence of unrecrystallized particle boundaries in the PPS alloy was also unbeneficial with regard to corrosion. The advantage of the LPBF and PPS processes was the ability to change the proportion of α(Mg) to β(Li), which when the complete consolidation of the material is achievable, may increase the corrosion resistance of dual-structured Mg-Li alloys. The results show that powder metallurgy routes have a wide potential to be used for the manufacture of Mg-Li based alloys.

Corrosion behavior of fine-grained Mg-7.5Li-3Al-1Zn fabricated by extrusion with a forward-backward rotating die(KoBo)

The microstructure-dependent corrosion resistance of dual structured fine-grained Mg-7.5 Li-3 Al-lZn has been investigated.The alloys were extruded using extrusion with a forward-backward rotating die(KoBo,a newly developed SPD method)at two different extrusion ratios.The fine-grained microstructures formed in the alloys were characterized,and the influence of grain refinement on corrosion resistance was analyzed.For fine-grained(α+β)Mg-Li alloys,a higher extrusion ratio led to more intensive grain refinement;however,this relationship did not improve their corrosion resistance in a chloride-containing solution.The corrosion resistance of the alloys was mainly controlled by the refinement ofα(Mg)andβ(Li),along with the distribution of second phases.The presence of MgLi_(2) Al at grain boundaries facilitated their dissolution.