Microstructure analysis of the as-extruded AZ31 alloy bar: (a) schematic of two selected surfaces for EBSD analysis; (b) and (c) EBSD orientation maps to the grain structure of the “TS” and “LS” samples, respectively. The inserts in images (b) and (c) are the stereographic triangles or inverse pole figures reflecting the orientation relationship between sample surfaces and crystallographic planes of grains.

 Hydrogen evolution versus immersion time curves of two differently oriented samples measured in PBS solution at the OCP. Macro corrosion morphologies of the two surfaces after immersion for 48?h are inserted in the graph.

 Potentiodynamic polarization curves of two differently oriented sample surfaces after immersion in PBS solution for 10?min and 48?h, respectively.

 Surface morphology of the “TS” sample immersed in PBS solution for different time intervals: (a) 2?h, (b) 4?h, (c) 24?h and (d) 48?h. Image (e) is the EDS result of the degraded area labeled in image (d).

 Surface morphology of the “LS” sample immersed in PBS solution for different time intervals: (a) 2?h, (b) 4?h, (c) 24?h and (d) 48?h. Image (e) is the EDS result of the degraded area labeled in image (d).

 Cross-sectional microstructure of differently oriented samples immersed in PBS solution for different time intervals: (a) and (c) “TS” samples after immersion for 8?h and 24?h, (b) and (d) “LS” samples after immersion for 8?h and 24?h.

 Elemental depth profiles of differently oriented sample surfaces after immersion in PBS solution for 10?min: (a) “TS” and (b) “LS” samples.

 Typical XPS deconvolved spectra of surface film for the “TS” sample immersed in PBS solution for 10?min: (a) Mg-1s, (b) O-1s and (c) P-2p.

 Typical XPS deconvolved spectra of surface film for the “LS” sample immersed in PBS solution for 10?min: (a) Mg-1s, (b) O-1s and (c) P-2p.