Fig. 1 Photographs of as-received AZ31 pretreated by a pure AcOH,b 300 g/L AcOH, c 100 g/L AcOH and d pure Ac2O for 30 s. e As-received AZ31

Fig. 2 XPS spectra of Mg 2p and KL2,3L2,3 for a, b as-received and c, d Ac2O-pretreated AZ31 samples

Fig. 3 XPS spectra of a Mg 2p and b( Mg KL2,3L2,3 for as-received AZ31 sample after Ar-ion sputtering. c C 1 s spectra of the as-received (black) and Ac2O-pretreated (red) AZ31 samples

Fig. 4 Surface SEM images of a as-received, b polished, and c Ac2O-pretreated AZ31 samples

Fig. 5 Schematic illustrations of Ac2O pretreatment for as-received AZ31

Fig. 6 Linear sweep voltammograms for AZ31 working electrodes immersed in the G2-AlCl3 bath; black: as-received, blue: polished, and red: Ac2O-pretreated

Fig. 7 Surface SEM images of a, d as-received, b, e polished, and c, f Ac2O-pretreated AZ31 after a-c immersing or d-f electrodeposition in G2-AlCl3 bath. Inset shows the photograph of sample, and the area below dotted line is immersed in bath

Fig. 8 XRD profiles of the a Ac2O-pretreated, b as-deposited, and c heat-treated AZ31 samples

Fig. 9 a Cross-sectional SEM image and b SEM-EDX mapping of the Al-coated AZ31 with Ac2O pretreatment

Fig. 10 (a) Surface SEM image, (b) cross-sectional SEM image, (c) cross-sectional EDX mapping, and (d) EDX line scan for the heat-treated AZ31 sample. Inset of (a) shows the photograph of the sample and points A-C in (c) indicate the points for nanoindentation test

Fig. 11 Al-Mg binary phase diagram (Ref. [36]). I, II, III&IV and V correspond to the composition of Al(Mg), Al(Mg)/Al3Mg2, Al3Mg2/Mg17Al12 and Mg17Al12/Mg(Al)

Fig. 12 a Polarization curves and b Nyquist plots of the as-received AZ31 substrate, as-deposited Al, and the heat-treated sample

Fig. 13 Load-depth curves for the a AZ31 substrate, as-deposited Al and b the heat-treated sample. A, B and C correspond to the positions shown in Fig. 7c, and the corresponding distance to surface is 2 μm, 10 μm, and 30 μm