Fabrication of Al-Coated Mg-Li Alloy Sheet and Investigation of Its Properties

doi:10.1007/s40195-018-0774-9

Abstract

Abstract:

An Al-coated Mg-8 mass% Li alloy rectangular bar was fabricated by hot extrusion, and then, it was hot-rolled into a thin sheet. The Al coating was uniform in thickness and had good bonding with the substrate during all the processing. This Al-coated Mg-Li alloy exhibited a good corrosion resistance in a 0.5 mass% HCl aqueous solution. No intermetallic compound was observed at the Al/Mg-Li interface after the extrusion and the rolling. The Al-coated Mg-Li alloy sheet exhibited an elongation to fracture of 35% at room temperature at a strain rate of 0.001 s^-1 without any debonding between the coating and the substrate. When tensile tested at 573 K at 0.001 s^-1 in the air, the Al coating remained undamaged even until an elongation of about 150%. Further elongation generated cracks on the coating and the specimen fractured at an elongation of about 200%. In an Ar atmosphere, the specimen exhibited a fracture elongation of over 400% under the same conditions at 573 K at 0.001 s^-1, although a large number of cracks generated on the Al coating.

Key words: Mg-Li alloy, Composite material, Coating, Mechanical properties, Superplasticity

Tian-Long Zhang, Toko Tokunaga, Munekazu Ohno, Mi-Lin Zhang, Kiyotaka Matsuura. Fabrication of Al-Coated Mg-Li Alloy Sheet and Investigation of Its Properties[J]. Acta Metallurgica Sinica (English Letters), 2019, 32(2): 169-177.

Figures/Tables 17

Fig. 1 Schematic of the hot extrusion equipment

Fig. 2 Schematic of the die

Fig. 3 Schematic drawings of tensile test specimen: a top view, b longitudinal section

Fig. 4 a Cross section of the as-extruded Al-coated Mg-Li alloy rectangular bar which is about 50 mm from the tip, b interface between Al coating and Mg-Li alloy substrate in the cross section. The extrusion direction corresponds to the normal to the figure

Fig. 5 Change of the coating thickness in the longitudinal direction of the as-extruded Al-coated Mg-Li alloy bar

Fig. 6 a Longitudinal section of the as-rolled Al-coated Mg-Li alloy sheet, b interface between Al-coating and Mg-Li-alloy substrates in the longitudinal section. The rolling direction corresponds to the traverse direction of the figures

Fig. 7 Nominal stress-strain curves of the as-rolled Al-coated Mg-Li alloy sheet at room temperature at 0.001 s-1

Fig. 8 Longitudinal section of the as-rolled Al-coated Mg-Li alloy sheet elongated to fracture at room temperature: a low magnified image, b high magnified image of the Al-coating part

Fig. 9 a SEM image of the intermetallic compound layer, b AES line profile showing the distribution of Li, Mg and Al at the Al/Mg-Li alloy interface after a heat treatment at 573 K for 60 min

Fig. 10 SEM images of the tensile fracture surface of the specimen: a as-rolled specimen without heat treatment, b specimen after a heat treatment at 573 K for 60 min

Fig. 11 EBSD image of the specimen before superplastic tensile test: a grain map, b phase map

Fig. 12 Stress-strain curves of the specimens tensile tested at temperatures from 448 K to 573 K in the air at strain rates of a 0.001 s-1, b 0.01 s-1

Fig. 13 Effects of strain rate on the flow stress of the Al-coated Mg-Li alloy sheet at different temperatures

Fig. 14 Longitudinal section of tensile specimen of the as-rolled Al-coated Mg-Li alloy sheet after a tensile elongation of 150% at 573 K at 0.001 s-1 in the air

Fig. 15 Tensile specimens of the Al-coated Mg-Li alloy at 573 K at 0.001 s-1 in the air and in an Ar atmosphere

Fig. 16 Cracks on the Al coating along about 45° to the tensile direction

Fig. 17 Weight loss of different samples in 0.5 mass% HCl aqueous solution

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