Fig. 1 Optical microscope images of the microstructure of dilute Mg-Al-Ca-Mn alloy: a A04, b A08, c A12

Fig. 2 X-ray diffraction pattern of A04, A08, and A12 of dilute Mg-Al-Ca-Mn alloy

Fig. 3 SEM images and EDS analysis of the microstructure of dilute Mg-Al-Ca-Mn alloy: a A04, b A08, c A12, d typical precipitation phase line scan analysis

Fig. 4 EBSD results obtained from three samples and grain size distribution histograms: a A04; b A08; c A12

Fig. 5 The (0001)/(10-10) pole figures of the three samples: a A04; b A08; c A12

Fig. 6 OCP of the dilute Mg-Al-Ca-Mn alloy for 7200 s and the surface state of the immersed sample in 3.5 wt% NaCl

Fig. 7 a A schematic polarization curve of extruded dilute Mg-Al-Ca-Mn alloy, b polarization curve of extruded dilute Mg-Al-Ca-Mn alloys after immersion in 3.5 wt% NaCl at 25?±?1 °C

Fig. 8 Hydrogen evolution rates as a function of immersion time of A04, A08, and A12 specimens in 3.5 wt% NaCl at 25?±?1 °C at a 7 d, b 12 h

Fig. 9 Average mass loss rate of A04, A08, and A12 specimens in 3.5 wt% NaCl at 25?±?1 °C

Fig. 10 Macromorphologies of A04, A08 and A12 samples after immersed in 3.5 wt% NaCl solutions for 7 d

Fig. 11 Typical corrosion morphologies of dilute Mg-Al-Ca-Mn alloys after immersion testing for 2 h and 7 d in 3.5 wt% NaCl at 25?±?1 °C: a,d A04; b,e A08; c,f A12

Fig. 12 X-ray diffraction patterns of dilute Mg–Al–Ca–Mn alloy immersed in 3.5 wt% NaCl at 25?±?1 °C for 1 h

Fig. 13 Electrochemical impedance spectra (EIS) plots of dilute Mg-Al-Ca-Mn alloys in 3.5 wt% NaCl at a,b 10 min, c,d 2 h

Fig. 14 a Changes in Al content, Mn content, impurity Fe content and Fe atomic ratio in Al-Mn phase of dilute Mg-Al-Ca-Mn alloys, b corrosion rate vs. Fe atomic ratio in Al-Mn phase of dilute Mg-Al-Ca-Mn alloys